Insulin Responses in Equivocal and Definite Diabetes, with Special Reference to Subjects Who Had Mild Glucose Intolerance but Later Developed Definite Diabetes

Abstract

Insulin secretory responses during the 100 g glucose tolerance test (GTT) were studied in subjects who had or had had glucose intolerance. Patients who had metabolic diseases other than diabetes were excluded. The ratio (.DELTA.IRI/.DELTA.BS) of increments of blood insulin to blood sugar 30 min after glucose load was used as the most sensitive index to detect the abnormality of early insulin release in diabetes. In patients with definite diabetes (i.e., those whose fasting blood sugar values (FBS) were or had been higher than 140 mg/100 or who had diabetic retinopathy), .DELTA.IRI/.DELTA.BS ratios were almost invariably subnormal regardless of FBS levels and the types of glucose tolerance at the time of GTT. In the rest of the patients (equivocal diabetics), .DELTA.IRI/.DELTA.BS ratios were either normal or subnormal. The decrease in .DELTA.IRI/.DELTA.BS was a fairly stable characteristic of each individual; in 330 equivocal diabetics, only 28 cases (8.4%) moved between high- and low-insulin-responder groups during the follow-up. In 39 patients who had equivocal diabetes at the initial examination but subsequently developed definite diabetes (20 who began to have FBS above 140 mg/100 and 19 who developed retinopathy), the insulin response was already subnormal at the initial GTT and remained low throughout the follow-up periods, although their glucose tolerance varied between normal, borderline and diabetic types. Definite diabetes occurred exclusively in the low-insulin-responder group among equivocal diabetics. The decrease in insulin response to glucose seems to be a more inherent, specific and stable feature of true diabetes than glucose intolerance, because it precedes the occurrence and persists after the remission of derangement of carbohydrate metabolism in definite diabetes.