Insulin resistance during suckling period in rats.

Glucose metabolism was studied in 13- to 15-day-old suckling rats and 28- to 30-day-old rats weaned at 19 days on a high-carbohydrate, low-fat diet. The glucose turnover rate in the basal state was similar in suckling and weaned rats (14 mg X min-1 X kg-1). Glucose infusion (20 mg X min-1 X kg-1) produced a moderate hyperglycemia in weaned rats (150 mg/dl), whereas the suckling rats developed a high hyperglycemia (280 mg/dl), despite a large increase of plasma insulin concentration. The effect of insulin on glucose kinetics was then assessed by the euglycemic-hyperinsulinemic clamp technique. The plasma insulin levels reached were 736 +/- 87 microU/ml in the suckling and 444 +/- 34 microU/ml in the weaned rats, despite similar insulin infusion rates. Hepatic glucose production was suppressed by 90% in the weaned rats, whereas it remained at 40% of basal value in the suckling rats. The increase of glucose utilization above basal was fourfold higher in the weaned than in the suckling rats. Thus an insulin resistance state is present in the suckling rats and disappears after weaning onto a high-carbohydrate diet.