Hyperinsulinemia in Macaca nigra: precession to obesity and/or diabetes?

A subset of Macaca nigra have been identified with elevated levels of fasting and secretory insulin. The insulin increment between 0 and 15 min in an intravenous glucose tolerance test (IV-GTT) was 511 +/- 42 microU/ml in hyperinsulinemic (HYPER) monkeys compared to 191 +/- 16 microU/ml in nondiabetic (ND) controls (p less than 0.01). Fasting insulin increased from 37 +/- 4 in ND to 57 +/- 7 microU/ml in HYPER monkeys (p = 0.02). Glucose clearance also increased from 3.87 +/- 0.18 in ND to 5.78 +/- 0.52%/min in HYPER monkeys (p less than 0.01). The acute (239 +/- 31 versus 137 +/- 19 microU/ml/min) and secondary insulin responses (542 +/- 75 versus 207 +/- 32 microU/ml/min) were significantly greater in the HYPER monkeys than in the ND controls, respectively (p less than 0.05). The rate of glucose clearance per amount of insulin secreted was diminished about 40% in both the acute and the secondary phases of HYPER monkeys (p less than 0.02). Total C-peptide secretion was two times greater in HYPER than in ND monkeys (p = 0.05). The HYPER monkeys averaged 12-20% greater weight and 41-44% greater body mass than the ND monkeys (p less than 0.05), although both groups were fed the same amount of diet and were well within nonobese limits. These Macaca nigra appear to have a functional lesion with excess insulin secretion, relatively impaired clearance of glucose, and possible insulin resistance, but no islet pathological lesion. Development toward overt diabetes might be exacerbated if obesity became a more dominant factor.