Plasma insulin and C-peptide in relation to glucose intolerance in middle-aged men.

The relation between glucose homeostasis and insulin secretion (immunoreactive insulin and C-peptide) was studied in middle-aged males matched for age and body weight. Subjects with mild type II diabetes mellitus were compared to normals and to individuals with impaired glucose tolerance (IGT). In addition, the diabetics were subdivided according to duration, some of the subjects having recently deteriorated from IGT status. In the IGT individuals, there were no indications of a reduction in basal or glucose-induced insulin output. On the contrary, data indicate somewhat higher than normal secretion. Within the type II diabetics, those of short duration were largely similar to normals, whereas diabetes of longer duration was associated with some diminution in indices of B cell secretion. The data support the notion that a deficient insulin output is not a primary pathophysiological event in the development of type II diabetes.