SERUM-INSULIN AND GLUCOSE-CONCENTRATIONS IN PEOPLE AT RISK FOR TYPE-II DIABETES - A COMPARATIVE-STUDY OF AFRICAN-AMERICANS AND NIGERIANS

OBJECTIVE- To examine the phases of acute insulin release and glucose homeostasis in people of African descent with and without a positive f amily history of type II diabetes who reside in geographically diverse environments. The prevalence of type II diabetes in people of African descent varies considerably depending on the country of habitat. Fami ly history is recognized as an important risk factor for the developme nt of the disease. RESEARCH DESIGN AND METHODS - We studied serum gluc ose and insulin concentrations-before and after intravenous glucose ch allenge-in glucose-tolerant, first-degree relatives of African-America n (n = 18) and Nigerian (n = 20) type II diabetic patients and their r espective healthy control subjects (African American, n = 9; Nigerian, n = 18) living in their native countries. The acute first-(t = 0-5 mi n) and second-phase (t = 10-60 min) insulin releases were calculated a s the sum of incremental insulin responses to the intravenous glucose stimulation. RESULTS - Mean serum glucose levels and glucose decay con stant (K(G)) were not different in the African Americans and Nigerians . Fasting serum insulin in the African-American relatives was signific antly greater than the Nigerian relatives (16.0 +/- 3.0 vs. 5.8 +/- 1. 7 mU/L, P < 0.05). In contrast, FSI levels in the African-American con trol subjects were similar to Nigerian control subjects (6.3 +/- 1.4 v s. 4.5 +/- 1.8 mU/L). Acute first- and second-phase insulin levels wer e 2-3 times (P < 0.01) greater in African Americans than Nigerians, ir respective of family history of diabetes. Comparing the African-Americ an relatives with healthy control subjects, we found significantly (P < 0.05) higher FSI in the relatives; whereas the acute first-(272 +/- 44 vs. 222 +/- 55 mU/L) and second-phase (388 +/- 61 vs. 235 +/- 53 mU /L) serum insulin release tended to be greater, but not significantly different in the relatives. In contrast, the acute first (101 +/- 15 v s. 120 +/- 20 mU/L) and second phases (88 +/- 14 vs. 111 +/- 17 mU/1) of insulin release were slightly lower, but not significantly differen t, in the Nigerian relatives versus the Nigerian healthy control subje cts. In a subgroup of nonobese African-American (n = 11) and Nigerian (n = 11) relatives, and African-American (n = 8) and Nigerian (n = 7) healthy control subjects with a body mass index < 30 kg/m2, the mean f asting and post-stimulation serum glucose were not different. However, serum insulin concentrations in the African Americans were significan tly different from those of the Nigerians. The pattern of insulin resp onses in the nonobese subjects was similar to those of the respective African-American and Nigerian groups. CONCLUSIONS- our preliminary stu dy demonstrates greater serum insulin responses and, perhaps, insulin resistance in glucose-tolerant African Americans than in their Nigeria n counterparts, irrespective of family history of diabetes and obesity . We conclude that the antecedent lesions leading to the development o f type II diabetes may be different in the first-degree relatives of A frican-American and Nigerian diabetic patients.