Effect of age and weight on plasma glucose and insulin responses in the rat.

Plasma glucose and insulin responses to orally administered glucose were determined in rats of varying ages and weights. The results indicated that glucose tolerance tends to deteriorate as rats grow from 1 month to 9 months of age. This change in glucose tolerance was associated with an increase in the response of plasma insulin to glucose, consistent with the hypothesis that the decline in glucose tolerance is due to a loss of normal insulin sensitivity. The changes in glucose and insulin responses could not be explained entirely on the basis of the associated weight gain. They seemed to be at least partially secondary to either age or an age-related factor other than obesity.