HYPERPROINSULINEMIA OF TYPE-II DIABETES IS NOT PRESENT BEFORE THE DEVELOPMENT OF HYPERGLYCEMIA

OBJECTIVE - To examine proinsulin and insulin levels in first-degree r elatives of patients with non-insulin-dependent diabetes mellitus (NID DM). RESEARCH DESIGN AND METHODS - Comparison of insulin and proinsuli n responses to an oral glucose tolerance test in four groups of indivi duals: 1) 31 patients with newly diagnosed NIDDM treated with diet alo ne, 2) 34 first-degree relatives of NIDDM patients with impaired gluco se tolerance (IGT), 3) 26 relatives with normal glucose tolerance (NGT ), and 4) 30 subjects without a family history of diabetes. RESULTS- B oth fasting and post-glucose levels of proinsulin were elevated in pat ients with diabetes, but not in the relatives with IGT or NGT. Levels of true insulin were highest in the diabetic group, followed by the su bjects with IGT, and were lowest among relatives with NGT. Proinsulin levels correlated with glucose levels, suggesting that hyperglycemia i s the main stimulus for increased proinsulin secretion. CONCLUSIONS - First-degree relatives of NIDDM patients, who have a high risk of deve loping diabetes, do not exhibit elevated levels of fasting or glucose- stimulated proinsulin as long as their fasting glucose levels remain n ormal.