Sex differences of normal dogs in lipid mobilization and blood glucose levels after glucose or insulin infusion.

The influence of sex hormones on carbohydrate and lipid homeostasis was studied by comparing the response to glucose or insulin infusion in male and female dogs. The levels of blood glucose, serum immunoreactive insulin (IRI) and plasma free fatty acids (FFA) were determined. The hyperglycemia induced by glucose infusion (10 mg min-1 kg-1) for 60 min in summer was significantly higher in male than in female dogs. This sex difference in the response was confirmed in experiments performed in winter, when blood glucose levels of both sexes in response to the infusion reached higher values than those found in summer. The increase of serum IRI in response to glucose infusion was similar in both sexes in the summer experiment, while in winter the increase was significantly reduced and delayed in males. Glucose infusion into male and female dogs induced no significant changes in plasma FFA concentration in experiments carried out in winter or summer. Insulin infusion (16.6 mU min-1 kg-1) caused hypoglycemia in both sexes, which was of earlier onset in the females. The antilipolytic effect of insulin occurred in both sexes and was also stronger in females. The data show sexual and seasonal differences in response by dogs to glucose infusion and emphasize the participation of sex hormones in the homeostasis of energy substrates.