A Model of Chronic Nutrient Infusion in the Rat

Summary

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.

Abstract

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.

Introduction

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....

Protocol

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

1. Sterilize surgical instruments. Canulation tubing must also b....

Results

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±5 g before surgery and 588±6 g at the initiation of the infusion (mean±SE; n=37; P<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 a.......

Discussion

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 polyge.......

Materials

List of materials used in this article

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