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Abstract
Obesity and insulin resistance is a growing problem in people and in cats. Insulin resistance is defined as a condition in which the magnitude of the biological response to insulin is decreased. The major hallmarks of insulin resistance are alterations in glucose and lipid metabolism. Together, they lead to an impairment of insulin secretion and action, and may cause type 2 diabetes. Several methods have been developed in people in order to evaluate early changes in insulin secretion, glucose and lipid metabolism. The goal of this research was to examine the efficacy and sensitivity of different methods, such as the Euglycemic Hyperinsulinemic glucose Clamp (EHC), and the Frequently Sampled Intravenous Glucose Tolerance Test (FSIVGTT) to detect changes in insulin sensitivity, and to examine glucose and lipid metabolism by using labeled (3H)-glucose and deuterated glycerol and indirect calorimetry. Twenty two cats, 10 lean and 12 obese cats were used in this study. The EHC results of this study indicate that glucose sensitivity in obese cats is approximately 50% of that of lean cats and is negatively correlated with body weight, and that the insulin sensitivity for non-radioactive glucose was double that of radioactive glucose indicating that tracer estimates of insulin sensitivity may reflect only glucose disappearance while the estimate of insulin sensitivity based on total glucose also includes the suppression of hepatic glucose output Obese cats had higher baseline non esterified fatty acids (NEFA) concentrations than lean cats. Obese males had significantly higher baseline NEFA concentrations than obese females. Obese females had lower RER values than obese males cats during insulin infusion suggesting a higher capacity to oxidize fat than obese males. It is conclude that obesity in cats is characterized by increased lipid oxidation which is maintained in females during insulin infusion but not males. The lower heat production in lean males combined with a decreased ability to oxidize fatty acids in response to insulin may predispose them to obesity. The lower metabolic rate of obese cats of either gender favors an increase in body weight in the face of unaltered food intake