OBJECTIVE To assess the physiological role of first-phase insulin release in obese elderly patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS Moderately obese elderly patients (n = 14, mean age 77 ± 2 years, BMI 28.4 ± 0.7 kg/m²) with type 2 diabetes underwent three 180-min hyperglycemic clamp studies. In the control study, glucose alone was infused. In the first-phase study, human insulin was infused for the first 4 min at 12 mU/m² to mimic first-phase insulin release. In the first-phase enhanced study, insulin was infused for the first 4 min at 24 mU · m⁻² · min⁻¹. Tritiated glucose methodology was used in all studies to measure glucose production and disposal rates.

RESULTS Glucose values were similar in all studies. In the control study, first-phase insulin response was absent. The peak insulin response occurred at 4 min in the first-phase and first-phase enhanced studies, but insulin values were substantially higher in the latter study (528 ± 40 vs. 340 ± 24 pmol/l, P < 0.0001). Second-phase insulin responses were not different among the studies. Glucose production and disposal rates were not significantly different among the studies.

CONCLUSIONS While absent first-phase insulin secretion is a marker of abnormal pancreatic function in obese elderly patients with type 2 diabetes, it is not important in the regulation of hepatic glucose output or peripheral glucose disposal.