GLUCOSE AND INSULIN RESPONSES TO INTRAVENOUS GLUCOSE CHALLENGE IN RELATIVES OF NIGERIAN PATIENTS WITH NON-INSULIN-DEPENDENT DIABETES-MELLITUS

We analysed blood insulin and glucose concentrations before and during frequently sampled intravenous glucose tolerance tests (FSIGT) in 2 g roups of Nigerian subjects: (A) Control group (n = 18), without a posi tive family history of diabetes mellitus, and (B) Experimental group ( n = 16), comprising age-, sex- and body mass-matched first-degree rela tives of patients with non-insulin-dependent diabetes mellitus (NIDDM) . In comparison with Group A subjects, those in Group B had: (i) highe r fasting plasma glucose level (mean +/- S.E.M., 4.1 +/- 0.1 vs. 3.8 /- 0.11 mmol/l, P < 0.05); (ii) similar fasting serum insulin levels ( 6.7 +/- 5.0 vs. 5.8 +/- 5.6 mU/l, P = NS); (iii) lower mean incrementa l area under the first-phase (t = 0-10 min) post-glucose challenge ins ulin curve (376.9 +/- 8.8 vs. 435.6 +/- 5.6 mU/min l-1, P < 0.05); (iv ) increased incremental area under the second-phase (t = 10-182 min) p ost-glucose challenge insulin curve (432.9 +/- 11.5 vs. 161.3 +/- 8.7 mU/min l-1, P < 0.05); (v) reduced K(G), rate constant of glucose elim ination (0.97 +/- 0.12 vs. 1.41 +/- 0.12%/min, P < 0.05). These result s suggest that the subjects with a positive family history of NIDDM ha ve a reduced beta-cell insulin secretory reserve (from reduced first-p hase insulin response), tendency to rebound hyperinsulinemia during th e latter phase of the insulin secretory response, a degree of tissue i nsulin insensitivity (as evident from high fasting plasma glucose desp ite similar insulin levels) and a diminished glucose disposal rate, in comparison with subjects without a family history of NIDDM. These fea tures predict subsequent development of diabetes and suggest that as i n Caucasians, first-degree relatives of Nigerian patients with NIDDM a re at greater risk for future development of the disease.