EFFECT OF WEIGHT-GAIN AND SUBSEQUENT WEIGHT-LOSS ON GLUCOSE-TOLERANCEAND INSULIN-RESPONSE IN HEALTHY CATS

The effects of weight gain and subsequent weight loss on glucose toler ance and insulin response were evaluated in 12 healthy cats. Intraveno us glucose tolerance tests (IVGTT) were performed at entry into the st udy, after a significant gain of body weight induced by feeding palata ble commercial cat food ad libitum, after a significant loss of body w eight induced by feeding a poorly palatable purified diet to discourag e eating and promote fasting, and after recovery from fasting when bod y weight had returned to pre-study values and cats were eating commerc ial foods. A complete physical examination with measurement of body we ight was performed weekly, a CBC and serum biochemistry panel were eva luated at the time of each IVGTT, and a liver biopsy specimen obtained 2 to 4 days after each IVGTT was evaluated histologically for each ca t. Mean serum glucose and insulin concentrations after glucose infusio n and total amount of insulin secreted during the second 60 minutes an d entire 120 minutes after glucose infusion were significantly (P <.05 ) increased after weight gain, as compared with baseline. At the end o f weight loss, cats had hepatic lipidosis and serum biochemical abnorm alities consistent with feline hepatic lipidosis. There was a signific ant (P <.05) increase in mean serum glucose concentration and t(1/2), and a significant (P <.05) decrease in mean serum insulin concentratio n and the glucose disappearance coefficient (K) after glucose infusion for measurements obtained after weight loss, compared with those obta ined after weight gain and at baseline. Insulin peak response, insulin ogenic index, and total amount of insulin secreted during the initial 10 minutes, 20 minutes, and 60 minutes after glucose infusion were dec reased markedly (P <.05), compared with measurements obtained after we ight gain and at baseline. In addition, the total amount of insulin se creted for 120 minutes after glucose infusion was decreased markedly ( P < .05) in measurements obtained after weight loss, compared with tho se obtained after weight gain. At the end of recovery, all cats were v oluntarily consuming food, serum biochemical abnormalities identified after weight loss had resolved, the number and size of lipid vacuoles in hepatocytes had decreased, and results of IVGTT were similar to tho se obtained at baseline. These findings confirmed the reversibility of obesity-induced insulin resistance in cats, and documented initial de terioration in glucose tolerance and insulin response to glucose infus ion when weight toss was caused by severe restriction of caloric intak e.