Insulin secretory responses during the 100-gm. 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 (ΔIRI/ΔBS) of increments of blood insulin to blood sugar 30 minutes 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./lOO ml. or who had diabetic retinopathy), ΔIRI/ΔBS 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), ΔIRI/ΔBS ratios were either normal or subnormal. The decrease in ΔIRI/ΔBS was a fairly stable characteristic of each individual; in 330 equivocal diabetics, only 28 cases (8.4 per cent) 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./lOO ml. and 19 who developed retinopathy), the insulin response were 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. Thus, 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.

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