Insulin insensitivity and hyposuppressibility of glucagon by hyperglycemia in aged Wistar rats.

Insulin and glucagon secretion after glucose load and the hormone-receptor inter-action were compared between 6- and 24-month-old Wistar rats. The 24-month-old rats showed a failure to decrease glucagon secretion after glucose load in contrast to 6-month-old rats with a similar degree of glucose tolerance and insulin response. Age-related change of insulin receptor of rat livers was tentatively suggested to be a disappearance of the binding site with higher affinity. Affinity of the glucagon receptor did not differ significantly between the two groups. The hyposuppressibility of glucagon by hyperglycemia and the decrease of insulin affinity might contribute to the glucose intolerance with aging.