PHYSIOLOGICAL IMPORTANCE OF FIRST-PHASE INSULIN RELEASE IN ELDERLY PATIENTS WITH DIABETES

OBJECTIVE - To assess the physiological role of first-phase insulin re lease 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/m(2)) with type 2 diabetes underwent t hree 180-min hyperglycemic clamp studies, In the control study glucose alone was infused. In the first-phase study, human insulin was infuse d for the first 4 min at 12 mU/m(2) to mimic first-phase insulin relea se. In the first-phase enhanced study, insulin was infused for the fir st 4 min at 24 mU.m(-2).min(-1). Tritiated glucose methodology was use d in all studies to measure glucose production and disposal rates. RES ULTS - Glucose values were similar in all studies. In the control stud y, 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 respo nses were not different among the studies. Glucose production and disp osal rates were not significantly different among the studies. CONCLUS IONS - While absent first-phase insulin secretion is a marker of abnor mal pancreatic function in obese elderly patients with type 2 diabetes , it is not important in the regulation of hepatic glucose output or p eripheral glucose disposal.