This work was supported by the National Institutes of Health (R01DK58096 to Vincent Poitout). Vincent Poitout holds the Canada Research Chair in Diabetes and Pancreatic Beta-cell Function. Bader Zarrouki received post-doctoral fellowships from Merck and Eli Lilly. Ghislaine Font&eacute;s was supported by a post-doctoral fellowship from the Canadian Diabetes Association.

Overview: The procedure consists of catheterizing the right jugular vein and left carotid artery under general anesthesia; allowing a 7-day recuperation period; connecting the catheters to the pumps using a swivel and counterweight system that enables the animal to move freely in the cage; and infusing glucose and/or Intralipid (a soybean oil emulsion which generates a mixture of approximately 80% unsaturated/20% saturated fatty acids when infused with heparin 9) for 72 hr.
1. Canulation of the Right Jugular Vein and the Left Carotid Artery
<ol>
	<li>Sterilize surgical instruments. Canulation tubing must also be cold-sterilized using a liquid sterilizing agent (2.6% glutaraldehyde) prior to the procedure. Immerse the tubing in an autoclaved container for 16-24 hr. Rinse and flush thoroughly with sterile distilled water to remove all traces of glutaraldehyde before use.</li>
	<li>Weigh the rat to calculate drug dosages: 
	Carprofen 5 mg/kg: dilution 1/10 = Body weight (g) x 0.001 ml SC (analgesic) 
	Glycopyrrolate 0.01 mg/kg : dilution 1/10 = BW (g) X 0.0012 ml SC (anticholinergic)</li>
	<li>Anesthetize the rat using isoflurane and oxygen.</li>
	<li>Place the rat on its stomach. Shave the area behind the ears to the base of the shoulders. Lay the rat on its back. Shave the region under the neck to the front paws.</li>
	<li>Prep the surgical site with chlorhexidine, alcohol, and iodine. Administer drugs.</li>
	<li>Transfer the rat to the surgical field.</li>
	<li>Using aseptic technique, canulate the right jugular vein and the left carotid artery with a PE-50 canula attached to a 1 ml syringe filled with 5 U of heparinized saline. Flush the canulas with 50 U of heparinized saline to avoid clotting during the recovery period. Use blunted 23G needles. Close each canula with a 23G pin.</li>
	<li>After the surgery, trim approximately 2.5 mm off the bottom incisors and place the rat in an infusion jacket to prevent the canulas from being eaten.</li>
	<li>Provide oxygen (1 L/min for 10 min) to help evacuate isoflurane.</li>
	<li>Place the rat in a heated cage until it is fully awake.</li>
	<li>Operate four rats to use one per infusion condition (Table 1).</li>
</ol>
2. Post-operative Care (Post-surgical Treatment and Connection of the Catheters)
<ol>
	<li>Weigh the rats on day 1 and day 2 post-surgery.</li>
	<li>Administer glycopyrrolate (BW(g) x 0.00048 ml) SC twice on day 1 post-surgery and once on day 2 post-surgery.</li>
	<li>Additional supportive treatments can be administered if necessary: fluids, heating pad, wet diet, oxygen therapy, analgesics, anticholinergics.</li>
	<li>On day 7 post-surgery, weigh the rats to calculate the flow rates for infusion.</li>
	<li>Connect each rat to an infusion system using a tether and swivel mounted on a cage grill top (Figure 1).</li>
	<li>Flush the canulas with 5 U of heparinized saline to remove clots. Flush the canulas once more with 50 U of heparinized saline to prevent clotting.</li>
	<li>Allow the rats to acclimate to the tether and swivel for at least 24 hr before starting the infusion.</li>
</ol>
3. Infusion
<ol>
	<li>Draw 0.15 ml of blood from the carotid of each rat and measure glycemia. Flush the jugular canulas. Use 50 U of heparinized saline to prevent clotting in both canulas of each rat.</li>
	<li>Transfer the blood sample to a 0.5 ml collection tube containing 2% EDTA. Centrifuge at 10,000 rpm for 2 min and freeze the plasma at -20 &deg;C.</li>
	<li>Fill two 60 ml syringes for each of the infusion conditions listed below. Place Syringe 1 on the front position of the pump and place Syringe 2 on the back position of the pump.</li>
	<li>Join each pair of solutions together with y-connectors and CO-EX T22 tubing that has been sterilized. Place the syringes on a Harvard 33 dual syringe pump.</li>
	<li>Change the cage bottom and remove all food from the cage grill top.</li>
	<li>Weigh 150 g of standard chow and place on the cage grill top.</li>
	<li>Connect the syringes to the swivel on the cage grill. Flush the syringes properly to remove trapped air from the lines.</li>
	<li>Calculate the infusion flow rates using the body weight that was taken prior to connecting the rat to the infusion system. Rates are calculated with a Microsoft Excel file that converts the glucose infusion rate (GIR) into ml/h.</li>
	<li>Set the pump to administer flow rates for 60 ml syringes according to the manufacturer's settings. Enter the rate for Syringe 1 (front syringe) and the rate for Syringe 2 (back syringe).</li>
	<li>Start the pump.</li>
</ol>
4. Monitoring
<ol>
	<li>After starting the pump, verify that there is no leaking from the swivel or from the canulas and that infusion tubing is not twisted. Also verify that there are no air bubbles in the tubing.</li>
	<li>After 3 hr of infusion, take a blood sample to monitor glycemia. Repeat after 6, 24, 48, and 72 hr of infusion. As a precaution, glycemia is also monitored after 30, 34, 54, and 60 hr of the infusion. Blood glucose can be measured using one drop of whole blood using a portable glucose monitor. This limits the amount of blood drawn during the infusion and therefore avoids significantly altering blood volume and/or hematocrit.</li>
	<li>The rate for Syringe 1 is modified based on glycemia values to maintain blood glucose at 220-250 mg/dl. The rate for Syringe 2 does not change during the 72 hr of infusion because free fatty acids are maintained at 1 mmol/L.</li>
	<li>Infusion conditions are paired so that the volume received for the control animals is equivalent to the volume received for the test animals (Table 1).</li>
	<li>After 24 hr of infusion, change the cage bottom and weigh the food remaining in the cage grill. Return the uneaten portion to the cage grill. Repeat after 48 hr.</li>
	<li>Refill syringes daily as needed during the 72 hr of infusion.</li>
	<li>During the infusion, always observe the rat for any signs of inflammation or discomfort. Administer appropriate care if needed.</li>
</ol>
5. Post-infusion Euthanasia
<ol>
	<li class="jove_content">After 72 hr of infusion, rats are anesthetized intravenously with 0.5 ml of a ketamine/xylazine cocktail (182 mg/kg of ketamine and 11.6 mg/kg of xylazine diluted 1:2 with 0.9% NaCl).</li>
	<li class="jove_content">The toe-pinch reflex is used to verify the level of anesthesia. Additional anesthetic is administered as needed.</li>
	<li class="jove_content">When the rat is anesthetized, the abdominal cavity is opened with surgical scissors. The rat is exsanguinated by drawing 10-15 ml of blood in a syringe from the aorta or the vena cava.</li>
</ol>

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H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Minireview:+weapons+of+lean+body+mass+destruction:+the+role+of+ectopic+lipids+in+the+metabolic+syndrome.">Minireview: weapons of lean body mass destruction: the role of ectopic lipids in the metabolic syndrome.</a> Endocrinology. 144, 5159-5165 (2003).</li><li>Harmon, J. S., Gleason, C. E., Tanaka, Y., Poitout, V., Robertson, R. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antecedent+hyperglycemia,+not+hyperlipidemia,+is+associated+with+increased+islet+triacylglycerol+content+and+decreased+insulin+gene+mRNA+level+in+Zucker+diabetic+fatty+rats.">Antecedent hyperglycemia, not hyperlipidemia, is associated with increased islet triacylglycerol content and decreased insulin gene mRNA level in Zucker diabetic fatty rats.</a> Diabetes. 50, 2481-2486 (2001).</li><li>Bachar, E., Ariav, Y., Cerasi, E., Kaiser, N., Leibowitz, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neuronal+nitric+oxide+synthase+protects+the+pancreatic+beta+cell+from+glucolipotoxicity-induced+endoplasmic+reticulum+stress+and+apoptosis.">Neuronal nitric oxide synthase protects the pancreatic beta cell from glucolipotoxicity-induced endoplasmic reticulum stress and apoptosis.</a> Diabetologia. 53, 2177-2187 (2010).</li><li>Peyot, M. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Beta-cell+failure+in+diet-induced+obese+mice+stratified+according+to+body+weight+gain:+secretory+dysfunction+and+altered+islet+lipid+metabolism+without+steatosis+or+reduced+beta-cell+mass.">Beta-cell failure in diet-induced obese mice stratified according to body weight gain: secretory dysfunction and altered islet lipid metabolism without steatosis or reduced beta-cell mass.</a> Diabetes. 59, 2178-2187 (2010).</li><li>Hagman, D. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cyclical+and+alternating+infusions+of+glucose+and+intralipid+in+rats+inhibit+insulin+gene+expression+and+Pdx-1+binding+in+islets.">Cyclical and alternating infusions of glucose and intralipid in rats inhibit insulin gene expression and Pdx-1 binding in islets.</a> Diabetes. 57, 424-431 (2008).</li><li>Fontes, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Glucolipotoxicity+age-dependently+impairs+beta+cell+function+in+rats+despite+a+marked+increase+in+beta+cell+mass.">Glucolipotoxicity age-dependently impairs beta cell function in rats despite a marked increase in beta cell mass.</a> Diabetologia. 53, 2369-2379 (2010).</li><li>Stein, D. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Essentiality+of+circulating+fatty+acids+for+glucose-stimulated+insulin+secretion+in+the+fasted+rat.">Essentiality of circulating fatty acids for glucose-stimulated insulin secretion in the fasted rat.</a> J. Clin. Invest. 97, 2728-2735 (1996).</li><li>Leahy, J. L., Cooper, H. E., Weir, G. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Impaired+insulin+secretion+associated+with+near+normoglycemia.+Study+in+normal+rats+with+96-h+in+vivo+glucose+infusions.">Impaired insulin secretion associated with near normoglycemia. Study in normal rats with 96-h in vivo glucose infusions.</a> Diabetes. 36, 459-464 (1987).</li><li>Hager, S. R., Jochen, A. L., Kalkhoff, R. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Insulin+resistance+in+normal+rats+infused+with+glucose+for+72+h.">Insulin resistance in normal rats infused with glucose for 72 h.</a> The American Journal of Physiology. 260, 353-362 (1991).</li><li>Laybutt, D. R., Chisholm, D. J., Kraegen, E. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Specific+adaptations+in+muscle+and+adipose+tissue+in+response+to+chronic+systemic+glucose+oversupply+in+rats.">Specific adaptations in muscle and adipose tissue in response to chronic systemic glucose oversupply in rats.</a> The American Journal of Physiology. 273, E1-E9 (1997).</li><li>Jonas, J. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+glucose+stimulates+early+response+gene+c-Myc+expression+in+rat+pancreatic+beta+cells.">High glucose stimulates early response gene c-Myc expression in rat pancreatic beta cells.</a> The Journal of Biological Chemistry. 276, 35375-35381 (2001).</li><li>Tang, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Glucose-induced+beta+cell+dysfunction+in+vivo+in+rats:+link+between+oxidative+stress+and+endoplasmic+reticulum+stress.">Glucose-induced beta cell dysfunction in vivo in rats: link between oxidative stress and endoplasmic reticulum stress.</a> Diabetologia. 55, 1366-1379 (2012).</li><li>Alonso, L. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Glucose+infusion+in+mice:+a+new+model+to+induce+beta-cell+replication.">Glucose infusion in mice: a new model to induce beta-cell replication.</a> Diabetes. 56, 1792-1801 (2007).</li><li>Magnan, C., Gilbert, M., Kahn, B. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chronic+free+fatty+acid+infusion+in+rats+results+in+insulin+resistance+but+no+alteration+in+insulin-responsive+glucose+transporter+levels+in+skeletal+muscle.">Chronic free fatty acid infusion in rats results in insulin resistance but no alteration in insulin-responsive glucose transporter levels in skeletal muscle.</a> Lipids. 31, 1141-1149 (1996).</li><li>Goh, T. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lipid-induced+beta-cell+dysfunction+in+vivo+in+models+of+progressive+beta-cell+failure.">Lipid-induced beta-cell dysfunction in vivo in models of progressive beta-cell failure.</a> Am. J. Physiol. Endocrinol. Metab. 292, 549-560 (2007).</li><li>Pascoe, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Free+fatty+acids+block+glucose-induced+beta-cell+proliferation+in+mice+by+inducing+cell+cycle+inhibitors+p16+and+p18.">Free fatty acids block glucose-induced beta-cell proliferation in mice by inducing cell cycle inhibitors p16 and p18.</a> Diabetes. 61, 632-641 (2012).</li><li>Bell, C. G., Walley, A. J., Froguel, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+genetics+of+human+obesity.">The genetics of human obesity.</a> Nature Reviews. Genetics. 6, 221-234 (2005).</li><li>Fontes, G., Hagman, D. K., Latour, M. G., Semache, M., Poitout, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lack+of+preservation+of+insulin+gene+expression+by+a+glucagon-like+peptide+1+agonist+or+a+dipeptidyl+peptidase+4+inhibitor+in+an+in+vivo+model+of+glucolipotoxicity.">Lack of preservation of insulin gene expression by a glucagon-like peptide 1 agonist or a dipeptidyl peptidase 4 inhibitor in an in vivo model of glucolipotoxicity.</a> Diabetes Res. Clin. Pract. 87, 322-328 (2010).</li><li>Crawford, P. A., Schaffer, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metabolic+stress+in+the+myocardium:+Adaptations+of+gene+expression.">Metabolic stress in the myocardium: Adaptations of gene expression.</a> Journal of Molecular and Cellular Cardiology. , (2012).</li><li>Kewalramani, G., Bilan, P. J., Klip, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Muscle+insulin+resistance:+assault+by+lipids,+cytokines+and+local+macrophages.">Muscle insulin resistance: assault by lipids, cytokines and local macrophages.</a> Curr. Opin. Clin. Nutr. Metab Care. 13, 382-390 (2010).</li><li>Cusi, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+obesity+and+lipotoxicity+in+the+development+of+nonalcoholic+steatohepatitis:+pathophysiology+and+clinical+implications.">Role of obesity and lipotoxicity in the development of nonalcoholic steatohepatitis: pathophysiology and clinical implications.</a> Gastroenterology. 142, 711-725 (2012).</li></ol>

Vincent Poitout is co-founder of and received research contracts from B&ecirc;tagenex Inc., a contract research organization which offers the infusion model presented in this article as a commercial service.

Although a number of previous studies have employed chronic infusions of glucose (e.g. 10-15) or lipids (e.g. 16,17) in rodents, to our knowledge the combined infusion of both fuels has only been reported in mice 18. The chronic infusion model presented here offers several advantages to study the effects on nutrient excess on a variety of biological functions in rats. First, it does not involve genetically obese rodents, and since common obesity in humans is polygenic 19, the findings are therefore more likely to be relevant to the effects of nutrient oversupply in the general population. Second, this model offers the possibility to test the effects of different nutrients (particularly sugars or fats) at different circulating levels, by changing their nature and the infusion flow rate. Third, the IV route of administration enables the co-infusion of compounds or drugs together with the nutrients 20. Finally, the relatively short time frame of the experiment (72 hr vs. weeks for high-fat diet induced models) is cost- and time-effective for preclinical studies.
	This model also has some disadvantages and limitations. First, as any surgical model is requires highly trained and skilled personnel in aseptic surgery. Second, as mentioned in the Representative Results section the animals tend to compensate for the glucose infusion by increasing endogenous insulin secretion, which requires frequent monitoring of blood glucose levels and adjustments of the GIR to maintain the target blood glucose levels throughout the infusion. Third, the procedure is not easily applicable to mice, which would be required in order to use it in genetically modified animals. In our experience, catheterization of both jugular vein and carotid artery in mice in technically challenging and the easiest approach in these smaller animals is to place a jugular catheter for the infusion and to sample from a peripheral vessel. This, however considerably limits the volume and frequency of sampling during the infusion.
	Given the focus of our laboratory, we have used this model to study the mechanisms of glucolipotoxicity in the pancreatic beta-cell 7,8. However, it can be applied to study the effects of nutrient excess in any tissue and organ such as, but not limited to, the heart 21, skeletal muscle, 22, and liver 23.

Chronically elevated levels of glucose and lipids in the circulation have been proposed to contribute to the pathogenesis of type 2 diabetes by altering the function of several organs implicated in the maintenance of glucose homeostasis including, but not limited to, the pancreatic beta-cell (reviewed in 1). The glucotoxicity hypothesis posits that chronic hyperglycemia aggravates the beta-cell defect which gave rise to hyperglycemia in the first place, thus creating a vicious cycle and contributing to the deterioration of glucose control in type 2 diabetes patients. Likewise, the glucolipotoxicity hypothesis proposes that concomitant elevations of glucose and lipid levels, as often observed in type 2 diabetes, are detrimental to the beta cell.
	Deciphering the cellular and molecular mechanisms of the deleterious effects of chronically elevated nutrients on pancreatic beta-cell function is key to the understanding of the pathogenesis of type 2 diabetes 1. To that end, a large number of studies have examined the mechanisms of chronic nutrient excess ex vivo in isolated islets of Langerhans or in vitro in clonal, insulin-secreting cell lines. However, translation of the findings obtained in these model systems to the whole organism is complex, in particular because the concentrations of fatty acids used in cultured cells or islets rarely match the circulating levels in the vicinity of the beta cells in vivo 2. On the other hand, the mechanisms of beta-cell failure in response to nutrient excess have been examined in rodent models of diabetes, as exemplified by the Zucker Diabetic Fatty rat 3,4, the gerbil Psammomys obesus 5 and the high-fat diet-fed mouse 6. These models, however, are characterized by intrinsic metabolic abnormalities and are not easily amenable to manipulations of blood glucose and/or lipid levels in a more controlled and less chronic setting. To be able to alter circulating nutrient levels in a timeframe of days in otherwise normal animals, we have developed a chronic infusion model in normal rats which enables us to examine the effects of lipids and glucose, alone or in combination, on physiological parameters and function 7,8.

<table border="1">
		<tbody>
		 <tr>
			<td>Name of Reagent/Material</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		 </tr>
		 <tr>
			<td>Saline 0.9%</td>
			<td>BD</td>
			<td>JB1324</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Dextrose 70%</td>
			<td>McKesson</td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
			<td>Intralipid 20%</td>
			<td>Fresenius Kabi</td>
			<td>JB6023</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Metricide (Glutaraldehyde 2.6%)</td>
			<td>Metrex</td>
			<td>11-1401</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Heparin Sodium 10,000 USP u/ml</td>
			<td>PPC</td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
			<td>Carprofen</td>
			<td>Metacam</td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
			<td>Glycopyrrolate</td>
			<td>Sandoz</td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
			<td>Isoflurane</td>
			<td>Abbott</td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
			<td>Chlohexidine 2%</td>
			<td></td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
			<td>Alcohol 70%</td>
			<td></td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
			<td>Iodine</td>
			<td></td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
			<td>PE-50</td>
			<td>BD</td>
			<td>427411</td>
			<td></td>
		 </tr>
		 <tr>
			<td>CO-EX T22</td>
			<td>Instech Solomon</td>
			<td>BCOEX-T22</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Connector 22G</td>
			<td>Instech Solomon</td>
			<td>SC22/15</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Swivel 22G</td>
			<td>Instech Solomon</td>
			<td>375/22PS</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Y-Connector 22G</td>
			<td>Instech Solomon</td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
			<td>Counterbalance and arm</td>
			<td>Instech Solomon</td>
			<td>CM375BP</td>
			<td></td>
		 </tr>
		 <tr>
			<td>23 G blunted needles</td>
			<td>Instech Solomon</td>
			<td>LS23</td>
			<td></td>
		 </tr>
		 <tr>
			<td>23 G canulation pins</td>
			<td>Instech Solomon</td>
			<td>SP23/12</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Tethers (12 inch)</td>
			<td>Lomir</td>
			<td>RT12D</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Infusion jackets </td>
			<td>Lomir</td>
			<td>RJ01, RJ02, RJ03, RJ04</td>
			<td></td>
		 </tr>
		 <tr>
			<td>(SM-XL)</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Tether attachment piece</td>
			<td>Lomir</td>
			<td>RS T1</td>
			<td></td>
		 </tr>
		 <tr>
			<td>60 ml syringe</td>
			<td>BD</td>
			<td>309653</td>
			<td></td>
		 </tr>
		 <tr>
			<td>1 ml syringe</td>
			<td>BD</td>
			<td>309602</td>
			<td></td>
		 </tr>
		</tbody>
 </table>

a model of chronic nutrient infusion in the rat

Chronic exposure to excessive levels of nutrients is postulated to affect the function of several organs and tissues and to contribute to the development of the many complications associated with obesity and the metabolic syndrome, including type 2 diabetes. To study the mechanisms by which excessive levels of glucose and fatty acids affect the pancreatic beta-cell and the secretion of insulin, we have established a chronic nutrient infusion model in the rat. The procedure consists of catheterizing the right jugular vein and left carotid artery under general anesthesia; allowing a 7-day recuperation period; connecting the catheters to the pumps using a swivel and counterweight system that enables the animal to move freely in the cage; and infusing glucose and/or Intralipid (a soybean oil emulsion which generates a mixture of approximately 80% unsaturated/20% saturated fatty acids when infused with heparin) for 72 hr. This model offers several advantages, including the possibility to finely modulate the target levels of circulating glucose and fatty acids; the option to co-infuse pharmacological compounds; and the relatively short time frame as opposed to dietary models. It can be used to examine the mechanisms of nutrient-induced dysfunction in a variety of organs and to test the effectiveness of drugs in this context.

Out of a series of 42 rats which underwent surgery, 5 rats were lost during the post-operative period and 1 rat was lost during the infusion, representing an overall success rate of 86%. The average body weight of the 37 rats that were eventually infused was 608&plusmn;5 g before surgery and 588&plusmn;6 g at the initiation of the infusion (mean&plusmn;SE; n=37; P&lt;0.0001 by paired t-test). The following representative results were obtained in 2 infusion groups: Saline (SAL), and Glucose + Intralipid (GLU+IL). Figures 2A and 2B show blood glucose and fatty acid levels, respectively, during the 72-hr infusion period. By design, the glucose levels are maintained around 220-250 mg/dl throughout the infusion, based on regular measurements and adjustments of the glucose infusion rate (GIR) as shown in Figure 3. Rodents have a strong capacity to compensate for the glucose infusion by increasing endogenous insulin secretion. Therefore, the GIR must be increased during the course of the infusion for blood glucose levels to be maintained at a relative steady-state. Nevertheless, blood glucose levels tend to decrease towards the end of the infusion, as seen in Figure 2A. Since the animals are infused with caloric nutrients, they spontaneously decrease their food intake (Figure 4).
<table border="1">
	<tbody>
		<tr>
			<td>Infusion Condition</td>
			<td>Syringe 1 (front position)</td>
			<td>Syringe 2 (back position)</td>
		</tr>
		<tr>
			<td>1</td>
			<td>Dextrose 70%</td>
			<td>Saline</td>
		</tr>
		<tr>
			<td>2</td>
			<td>Saline</td>
			<td>Saline</td>
		</tr>
		<tr>
			<td>3</td>
			<td>Dextrose 70%</td>
			<td>Intralipid 20% + Heparin 20U/ml</td>
		</tr>
		<tr>
			<td>4</td>
			<td>Saline</td>
			<td>Intralipid 20% % + Heparin 20U/ml</td>
		</tr>
	</tbody>
</table>
Table 1. Infusion regimens.
<img alt="Figure 1" fo:content-width="4in" fo:src="/files/ftp_upload/50267/50267fig1highres.jpg" src="/files/ftp_upload/50267/50267fig1.jpg" /> 
Figure 1. Photograph of the infusion system showing the rat with the catheters in place and the tether, swivel, and counterbalance arm mounted on the cage grill.
<img alt="Figure 2" fo:content-width="4.8in" fo:src="/files/ftp_upload/50267/50267fig2highres.jpg" src="/files/ftp_upload/50267/50267fig2.jpg" /> 
Figure 2. Plasma levels of glucose (A) and free fatty acids (B) during infusion of saline (SAL) or co-infusion of glucose and Intralipid (GLU+IL) in 6-month old Wistar rats. Data are mean &plusmn; SEM of 3-4 animals in each group.
<img alt="Figure 3" src="/files/ftp_upload/50267/50267fig3.jpg" /> 
Figure 3. Adjustment of the glucose infusion rate during the co-infusion of glucose and Intralipid (GLU+IL) in 6-month old Wistar rats. Data are mean &plusmn; SEM of 4 animals.
<img alt="Figure 4" src="/files/ftp_upload/50267/50267fig4.jpg" /> 
Figure 4. Average daily food intake of 6-month old Wistar rats infused with saline (SAL) or co-infused with glucose and Intralipid (GLU+IL). Data are mean &plusmn; SEM of 3-4 animals in each group. **p&lt;0.01.

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A Model of Chronic Nutrient Infusion in the Rat

A protocol for chronic infusions of glucose and Intralipid in rats is described. This model can be used to study the impact of nutrient excess on organ function and physiological parameters.

Chronic exposure to excessive levels of nutrients is postulated to  affect the function of several organs and tissues and to contribute to the  ...

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Nanyang Technological University

Research

JoVE Journal

Medicine

12.6K Views.  CRCHUM. A protocol for chronic infusions of glucose and Intralipid in rats is described. This model can be used to study the impact of nutrient excess on organ function and physiological parameters.

Video: A Model of Chronic Nutrient Infusion in the Rat

Orthotopic Aortic Transplantation: A Rat Model to Study the Development of Chronic Vasculopathy

Research models of chronic rejection are essential to investigate pathobiological and pathophysiological processes during the development of transplant vasculopathy (TVP).
The commonly used animal model for cardiovascular chronic rejection studies is the heterotopic heart transplant model performed in laboratory rodents. This model is used widely in experiments since Ono and Lindsey (3) published their technique. To analyze the findings in the blood vessels, the heart has to be sectioned and all vessels have to be measured.
Another method to investigate chronic rejection in cardiovascular questionings is the aortic transplant model (1, 2). In the orthotopic aortic transplant model, the aorta can easily be histologically evaluated (2). The PVG-to-ACI model is especially useful for CAV studies, since acute vascular rejection is not a major confounding factor and Cyclosporin A (CsA) treatment does not prevent the development of CAV, similar to what we find in the clinical setting (4). A7-day period of CsA is required in this model to prevent acute rejection and to achieve long-term survival with the development of TVP.
This model can also be used to investigate acute cellular rejection and media necrosis in xenogeneic models (5).

This video demonstrates the orthotopic aortic transplant model as a simple model to study the development of transplant vasculopathy (TVP) in rats.

Research models of chronic rejection are essential to investigate pathobiological and pathophysiological processes during the development of transplant ...

Urinary Bladder Distention Evoked Visceromotor Responses as a Model for Bladder Pain in Mice

Approximately 3-8 million people in the United States suffer from interstitial cystitis/bladder pain syndrome (IC/BPS), a debilitating condition characterized by increased urgency and frequency of urination, as well as nocturia and general pelvic pain, especially upon bladder filling or voiding. Despite years of research, the cause of IC/BPS remains elusive and treatment strategies are unable to provide complete relief to patients. In order to study nervous system contributions to the condition, many animal models have been developed to mimic the pain and symptoms associated with IC/BPS. One such murine model is urinary bladder distension (UBD). In this model, compressed air of a specific pressure is delivered to the bladder of a lightly anesthetized animal over a set period of time. Throughout the procedure, wires in the superior oblique abdominal muscles record electrical activity from the muscle. This activity is known as the visceromotor response (VMR) and is a reliable and reproducible measure of nociception. Here, we describe the steps necessary to perform this technique in mice including surgical manipulations, physiological recording, and data analysis. With the use of this model, the coordination between primary sensory neurons, spinal cord secondary afferents, and higher central nervous system areas involved in bladder pain can be unraveled. This basic science knowledge can then be clinically translated to treat patients suffering from IC/BPS.

Approximately 3-8 million people in the United States suffer from interstitial cystitis/bladder pain syndrome (IC/BPS), a debilitating condition characterized in part by pelvic pain. In order to study nervous system contributions to the condition, a physiological model of urinary bladder pain is used in mice and rats.

Approximately 3-8 million people in the United States suffer from interstitial cystitis/bladder pain syndrome (IC/BPS), a debilitating condition ...

Slow-release Drug Delivery through Elvax 40W to the Rat Retina: Implications for the Treatment of Chronic Conditions

Diseases of the retina are difficult to treat as the retina lies deep within the eye. Invasive methods of drug delivery are often needed to treat these diseases. Chronic retinal diseases such as retinal oedema or neovascularization usually require multiple intraocular injections to effectively treat the condition. However, the risks associated with these injections increase with repeated delivery of the drug. Therefore, alternative delivery methods need to be established in order to minimize the risks of reinjection. Several other investigations have developed methods to deliver drugs over extended time, through materials capable of releasing chemicals slowly into the eye. In this investigation, we outline the use of Elvax 40W, a copolymer resin, to act as a vehicle for drug delivery to the adult rat retina. The resin is made and loaded with the drug. The drug-resin complex is then implanted into the vitreous cavity, where it will slowly release the drug over time. This method was tested using 2-amino-4-phosphonobutyrate (APB), a glutamate analogue that blocks the light response of the retina. It was demonstrated that the APB was slowly released from the resin, and was able to block the retinal response by 7 days after implantation. This indicates that slow-release drug delivery using this copolymer resin is effective for treating the retina, and could be used therapeutically with further testing.

This paper details how Elvax 40W can be used as a slow-release method for drug delivery to the adult rat retina. The protocol for preparing, loading, and delivering the drug-resin complex to the eye is described.

Diseases of the retina are difficult to treat as the retina lies deep within the eye. Invasive methods of drug delivery are often needed to treat these ...

Neurodegeneration in an Animal Model of Chronic Amyloid-beta Oligomer Infusion Is Counteracted by Antibody Treatment Infused with Osmotic Pumps

Decline in hippocampal-dependent explicit memory (memory for facts and events) is one of the earliest clinical symptom of Alzheimer&#39;s disease (AD). It is well established that synapse loss and ensuing neurodegeneration are the best predictors for memory impairments in AD. Latest studies have emphasized the neurotoxic role of soluble amyloid-beta oligomers (A&#946;o) that begin to accumulate in the human brain approximately 10 to 15 yr before the clinical symptoms become apparent. Many reports indicate that soluble A&#946;o correlate with memory deficits in AD models and humans. The A&#946;o-induced neurodegeneration observed in neuronal and brain slice cultures has been more challenging to reproduce in many animal models. The model of repeated A&#946;o infusions shown here overcome this issue and allow addressing two key domains for developing new disease modifying therapies: identify biological markers to diagnose early AD, and determine the molecular mechanisms underpinning A&#946;o-induced memory deficits at the onset of AD. Since soluble A&#946;o aggregate relatively fast into insoluble A&#946; fibrils that correlate poorly with the clinical state of patients, soluble A&#946;o are prepared freshly and injected once per day during six days to produce marked cell death in the hippocampus. We used cannula specially design for simultaneous infusions of A&#946;o and continuous infusion of A&#946;o antibody (6E10) in the hippocampus using osmotic pumps. This innovative in vivo method can now be used in preclinical studies to validate the efficiency of new AD therapies that might prevent the deposition and neurotoxicity of A&#946;o in pre-dementia patients.

To study the effects of A&#946;o in vivo, we developed a model based on repeated hippocampal infusions of soluble A&#946;o coupled with continuous infusion of A&#946;o antibody (6E10) in the hippocampus using osmotic pumps to counteract the neurotoxic effect of A&#946;o.

Decline in hippocampal-dependent explicit memory (memory for facts and events) is one of the earliest clinical symptom of Alzheimer&#39;s disease (AD). It ...

Use of a Central Venous Line for Fluids, Drugs and Nutrient Administration in a Mouse Model of Critical Illness

This protocol describes a centrally catheterized mouse model of prolonged critical illness. We combine the cecal ligation and puncture method to induce sepsis with the use of a central venous line for fluids, drugs and nutrient administration to mimic the human clinical setting. Critically ill patients require intensive medical support in order to survive. While the majority of patients will recover within a few days, about a quarter of the patients need prolonged intensive care and are at high risk of dying from non-resolving multiple organ failure. Furthermore, the prolonged phase of critical illness is hallmarked by profound muscle weakness, and endocrine and metabolic changes, of which the pathogenesis is currently incompletely understood. The most widely used animal model in critical care research is the cecal ligation and puncture model to induce sepsis. This is a very reproducible model, with acute inflammatory and hemodynamic changes similar to human sepsis, which is designed to study the acute phase of critical illness. However, this model is hallmarked by a high lethality, which is different from the clinical human situation, and is not developed to study the prolonged phase of critical illness. Therefore, we adapted the technique by placing a central venous catheter in the jugular vein allowing us to administer clinically relevant supportive care, to better mimic the human clinical situation of critical illness. This mouse model requires an extensive surgical procedure and daily intensive care of the animals, but it results in a relevant model of the acute and prolonged phase of critical illness.

This protocol describes a centrally catheterized mouse model of prolonged critical illness. We combine the cecal ligation and puncture method to induce sepsis with the use of a central venous line for fluids, drugs and nutrient administration to mimic the human clinical setting.

This protocol describes a centrally catheterized mouse model of prolonged critical illness. We combine the cecal ligation and puncture method to induce ...

Isometric Contractility Measurement of the Mouse Mesenteric Artery Using Wire Myography

The wire myograph technique is used to assess the contractility of vascular smooth muscles in response to depolarization, GPCR agonists/inhibitors and drugs. It is widely used in many studies on the physiological functions of vascular smooth muscle, the pathogenesis of vascular diseases such as hypertension, and the development of smooth muscle relaxant drugs. The mouse is a widely used model animal with a large pool of disease models and genetically modified strains. We introduced this method to measure the isometric contraction of mouse mesenteric artery in detail. A 1.4-mm segment of mouse mesenteric resistance artery was isolated and mounted on a myograph chamber by passing two steel wires through its lumen. After equilibration and normalization steps, the vessel segment was potentiated by a high-K+ solution twice prior to the contraction assay. As an example of the application of this method in drug development, we measured the relaxant effect of a novel natural substance, neoliensinine, isolated from a Chinese herb, embryos of the lotus seed (Nelumbo nucifera Gaertn.) on mouse mesenteric arteries. The vessel segments mounted on the myograph chamber were stimulated with a high-K+ solution. When the force tension reached a stable sustained phase, cumulative doses of neoliensinine were added to the chamber. We found that neoliensinine had a dose-dependent relaxant effect on smooth muscle contraction, thus suggesting that it bears potential activity against hypertension. In addition, as the vessel segment can survive at least 4 hours after mounting and maintain contractility induced by the high-K+ solution for many times, we suggest that the wire myograph system may be used for the time-consuming process of drug screening.

The wire myograph technique is used to investigate vascular smooth muscle functions and screen new drugs. We report a detailed protocol for measuring the isometric contractility of the mouse mesenteric artery and for screening new relaxants of vascular smooth muscle.

The wire myograph technique is used to assess the contractility of vascular smooth muscles in response to depolarization, GPCR agonists/inhibitors and ...

A New Best Practice for Validating Tail Vein Injections in Rat with Near-infrared-Labeled Agents

Intravenous (IV) administration of agents into the tail vein of rats can be both difficult and inconsistent. Optimizing tail vein injections is a key part of many experimental procedures where reagents need to be introduced directly into the bloodstream. Unwittingly, the injection can be subcutaneous, possibly altering the scientific outcomes. Utilizing a nanoemulsion-based biological probe with an incorporated near-infrared fluorescent (NIRF) dye, this method offers the capability of imaging a successful tail vein injection in vivo. With the use of a NIRF imager, images are taken before and after the injection of the agent. An acceptable IV injection is then qualitatively or quantitatively determined based on the intensity of the NIRF signal at the site of injection.

Here we present a method to validate tail vein injections in rats by utilizing near-infrared fluorescence imaging data from dyes incorporated into agents or biological probes. The tail is imaged before and after the injection, the fluorescent signal is quantified, and an assessment of the injection quality is made.

Intravenous (IV) administration of agents into the tail vein of rats can be both difficult and inconsistent. Optimizing tail vein injections is a key part ...

Acupuncture in a Rat Model of Asthma

A high platform can fix rats without restriction and completely expose the acupoints on the back during acupuncture manipulation. This article describes methods for the fabrication of the high platform, establishes a rat model of asthma and measures changes in respiratory function using a noninvasive and real-time whole-body plethysmography (WBP) system.

A high platform can fix rats without restriction and completely expose the acupoints on the back during acupuncture manipulation. This article describes ...

A Mouse Model for Chronic Pancreatitis via Bile Duct TNBS Infusion

Chronic pancreatitis (CP) is a complex disease involving pancreatic inflammation and fibrosis, glandular atrophy, abdominal pain and other symptoms. Several rodent models have been developed to study CP, of which the bile duct 2,4,6 -trinitrobenzene sulfonic acid (TNBS) infusion model replicates the features of neuropathic pain seen in CP. However, bile duct drug infusion in mice is technically challenging. This protocol demonstrates the procedure of bile duct TNBS infusion for generation of a CP mouse model. TNBS was infused into the pancreas through the ampulla of Vater in the duodenum. This protocol optimized drug volume, surgical techniques, and drug handling during the procedure. TNBS-treated mice showed features of CP as reflected by bodyweight and pancreas weight reductions, changes in pain-associated behaviors, and abnormal pancreatic morphology. With these improvements, mortality associated with TNBS injection was minimal. This procedure is not only critical in generating pancreatic disease models but is also useful in local pancreatic drug delivery.

Chronic pancreatitis (CP) is a disease characterized by inflammation and fibrosis of the pancreas, often associated with intractable abdominal pain. This article focuses on refining the technique to generate a mouse model of CP via bile duct infusion with 2,4,6 -trinitrobenzene sulfonic acid (TNBS).

Chronic pancreatitis (CP) is a complex disease involving pancreatic inflammation and fibrosis, glandular atrophy, abdominal pain and other symptoms. ...

A Rat Lung Transplantation Model of Warm Ischemia/Reperfusion Injury: Optimizations to Improve Outcomes

From our experience with rat lung transplantation, we have found several areas for improvement. Information in the existing literature regarding methods for choosing appropriate cuff sizes for the pulmonary vein (PV), pulmonary artery (PA), or bronchus (Br) are varied, thus making the determination of proper cuff size during rat lung transplantation an exercise of trial and error. By standardizing the cuffing technique to use the smallest effective cuff appropriate for the size of the vessel or bronchus, one can make the transplantation procedure safer, faster, and more successful. Since diameters of the PV, PA, and Br are related to the body weight of the rat, we present a strategy to choosing an appropriate size using a weight-based guide. Since lung volume is also related to body weight, we recommend that this relationship should also be considered when choosing the proper volume of air for donor lung inflation during warm ischemia as well as for the proper volume of PBS to be instilled during bronchoalveolar lavage (BAL) fluid collection. We also describe methods for 4th intercostal space dissection, wound closure, and sample collection from both the native and transplanted lobes.

Here, we present optimizations to a rat lung transplantation model that serve to improve outcomes. We provide a size guide for cuffs based on body weight, a measurement strategy to ascertain the 4th intercostal space, and methods of wound closure and BAL (bronchoalveolar lavage) fluid and tissue collection.

From our experience with rat lung transplantation, we have found several areas for improvement. Information in the existing literature regarding methods ...