Influence of Glucose Dosage on Interpretation of Intravenous Glucose Tolerance Tests in Lean and Obese Cats

Abstract

Intravenous glucose tolerance tests (IVGTTs) are used in cats and other species to assess insulin sensitivity. Several dosages have been reported but the dosage that maximally stimulates insulin secretion in cats has not been determined nor has it been compared in lean and obese animals. IVGTTs were performed in 4 lean and 4 obese spayed female cats with 5 glucose dosages: 0.3 (A), 0.5 (B), 0.8 (C), 1.0 (D), and 1.3 (E) g/kg body weight (BW). Each cat received each dosage in a random design. The glucose disposal rate was significantly different only between lean and obese cats at the highest glucose dosage. The area under the curve for insulin increased significantly among A, B, C, and D in lean and among A, B, and C in obese cats but not between D and E in lean and among C, D, and E in obese cats. Baseline insulin secretion was significantly higher (P ϭ .03) and 1st peak insulin secretion was approximately 50% lower in obese as compared to lean cats (P ϭ .03). Lean but not obese cats reached baseline insulin concentrations at all dosages at 120 minutes. We conclude that the glucose dosage for maximal insulin secretion is 1.0 g/ kg BW in lean and 0.8 g/kg BW in obese cats, supporting routine use of 1 g/kg BW to maximally stimulate insulin secretion regardless of body composition. Obese cats showed an abnormal insulin secretion pattern, indicating a defect in insulin secretion with obesity and insulin resistance.Key words: Insulin; Resistance; Secretion. Intravenous glucose tolerance tests (IVGTTs) often are used to test beta cell function. The IVGTT is a sensitive test because glucose recognition has been shown to be lost early in the process of beta cell damage or impairment. The IVGTT is used to document glucose tolerance and insulin sensitivity. It is an excellent test to examine alterations in the insulin secretion pattern, which are the earliest signs of beta cell dysfunction in many species, including humans and cats.2-4 Although a dose-response study for glucose has been reported in the dog, similar studies have not been reported for the cat. The purpose of this study was to standardize the IVGTT with establishment of the optimal glucose dosage to achieve maximal insulin secretion and glucose disposal in lean and obese cats. Materials and MethodsFour lean and 4 obese female spayed adult purpose-bred cats a were used in this study. The body fat in the obese cats measured with dual emission x-ray absorptiometry was 50 Ϯ 3% higher than their body fat when they were lean. Their body weight was 44 Ϯ 4% higher than their lean body weight. The cats were maintained at the University of Georgia College of Veterinary Medicine Animal Care Facility under standard colony conditions. They were housed in individual cages and were given free access to water. Animal studies were approved by the University of Georgia Animal Care and Use Committee and conducted in accordance with guidelines established by the Animal Welfare Act and the National Institutes of Health Guide for the Care and Use of Laboratory Animals. The anima...

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