Glucose tolerance and insulin response in normal-weight and obese cats

SUMMARY Glucose tolerance and insulin response were evaluated in 9 normal-weight and 6 obese cats after iv administration of 0.5 g of glucose/kg of body weight. Blood samples for glucose and insulin determinations were collected immediately prior to and 2.5, 5, 7.5, 10, 15, 30, 45, 60, 90, and 120 minutes after glucose infusion. Baseline glucose concentrations were not significantly different between normal-weight and obese cats; however, mean ± sem glucose tolerance was significantly impaired in obese vs normal-weight cats after glucose infusion (half time for glucose disappearance in serum—77 ± 7 vs 51 ± 4 minutes, P < 0.01; glucose disappearance coefficient—0.95 ± 0.10 vs 1.44 ± 0.10%/min, P < 0.01; insulinogenic index—0.20 ± 0.02 vs 0.12 ± 0.01, P < 0.005, respectively). Baseline serum insulin concentrations were not significantly different between obese and normal-weight cats. Insulin peak response after glucose infusion was significantly ( P < 0.005) greater in obese than in normal-weight cats. Insulin secretion during the first 60 minutes ( P < 0.02), second 60 minutes ( P < 0.001), and total 120 minutes ( P < 0.0003) after glucose infusion was also significantly greater in obese than in normal-weight cats. Most insulin was secreted during the first hour after glucose infusion in normal-weight cats and during the second hour in obese cats. The impaired glucose tolerance and altered insulin response to glucose infusion in the obese cats was believed to be attributable to deleterious effects of obesity on insulin action and β-cell responsiveness to stimuli (ie, glucose).