Increased Gastric Inhibitory Polypeptide Is not Reduced in Patients with Noninsulin-Dependent Diabetes Mellitus Treated with Intense Insulin Therapy

Serum glucose and gastric inhibitory polypeptide (GIP) responses during mixed test meals and primed continuous infusion of insulin using the insulin clamp technique were studied in nine patients with noninsulin-dependent diabetes mellitus (NIDDM) before and after vigorous insulin treatment. Fasting serum glucose concentrations fell an average of 167 mg/dl (P < 0.001), and there was a 67% reduction (P < 0.001) in the postprandial glucose response. Mean hemoglobin Aic declined and paralleled the fall in serum glucose concentrations (9.2 ± 0.5% to 5.9% ± 0.3% P < 0.01). This improvement in glycemic control, however, was not associated with any appreciable change in GIP secretion. Basal and meal-stimulated serum GIP levels were not reduced after intense insulin therapy. Furthermore, hyperinsulinemia at physiological (100 μU/ml) and superphysiological (1000 μU/ml) levels failed to reduce GIP secretion before and after insulin therapy. Before insulin therapy, seven patients had elevated basal GIP levels and fiv...