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 groups of Nigerian subjects: (A) Control group (n = 18), without a positive family history of diabetes mellitus, and (B) Experimental group (n = 16), comprising age-, sex- and body mass-matched first-degree relatives of patients with non-insulin-dependent diabetes mellitus (NIDDM). In comparison with Group A subjects, those in Group B had: (i) higher 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 incremental area under the first-phase (t = 0–10 min) post-glucose challenge insulin 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) post-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 elimination (0.97 ± 0.12 vs. 1.41 ± 0.12%/min, P < 0.05). These results suggest that the subjects with a positive family history of NIDDM have a reduced beta-cell insulin secretory reserve (from reduced first-phase insulin response), tendency to rebound hyperinsulinemia during the latter phase of the insulin secretory response, a degree of tissue insulin insensitivity (as evident from high fasting plasma glucose despite similar insulin levels) and a diminished glucose disposal rate, in comparison with subjects without a family history of NIDDM. These features predict subsequent development of diabetes and suggest that as in Caucasians, first-degree relatives of Nigerian patients with NIDDM are at greater risk for future development of the disease.