Beta-cell hyperresponsiveness: earliest event in development of diabetes in monkeys.

Diabetes develops spontaneously in some, but not all, obese middle-aged monkeys. Longitudinal study of spontaneously obese rhesus monkeys has now shown the separation in time of the onset of various abnormalities associated with non-insulin-dependent diabetes mellitus (NIDDM). Glucose tolerance and acute and late insulin release were assessed at 6-mo to 1-yr intervals over a period of 7 yr in six young, lean, normal animals and 14 middle-aged obese, initially normoglycemic monkeys. Over 2-5 yr, while under study, five of the obese subjects developed overt diabetes [fasting plasma glucose greater than 140 mg/dl and decreased glucose disappearance rates (KG) less than 1.5]. Progressively increasing hyperinsulinemia leading to a 10-fold increase in basal plasma insulin levels (mean +/- SE = 443 +/- 69 microU/ml) and a fivefold increase in insulin response to glucose occurred independent of degree of obesity and before hyperglycemia. Later, basal and stimulated insulin levels declined before significant hyperglycemia. We conclude that in the monkey beta-cell function is clearly enhanced, not reduced, in the earliest stages of the progression to NIDDM but is reduced just before overt diabetes.