Insulin secretory responses in patients with glucose intolerance due to extra-pancreatic causes. comparison with idiopathic diabetes mellitus.

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Abstract
Insulin responses during 100 g glucose tolerance tests (GTT) were compared between 3 groups of patients with varying degrees of glucose intolerance. Patients who had no disease known to be associated with secondary diabetes were classified as patients with idiopathic diabetes mellitus. Those whose present and past fasting blood glucose (FBG) exceeded 140 mg/100 ml were assigned to group A, and the rest of the patients to group B. Group C included patients with liver disease, thyrotoxicosis, or myocardial infarction, or those treated with corticosteroids or who had undergone gastrectomy. Patients in group A consistently had subnormal insulin responses whether glucose tolerance was normal (i.e., previous abnormality of glucose tolerance), borderline or diabetic. Patients in group C without fasting hyperglycemia had enhanced rather than decreased insulin responses when glucose tolerance was the more impaired. Patients in group B had insulin responses similar to those either of group A or of group C. The relationship between the sum of 6 insulin and 6 blood glucose values during GTT (.SIGMA.IRI and .SIGMA.BG) was examined. The .SIGMA.BG-.SIGMA.IRI plot revealed distinctly different distribution zones for group A and group C (Zones A and C). In group A, .SIGMA.IRI values were < 300 .mu.U/ml irrespective of .SIGMA.BG values. In group C, .SIGMA.IRI tended to increase, paralleling the increase in .SIGMA.BG values in the range of .SIGMA.BG values < 1400 mg/100 ml. In patients whose .SIGMA.BG rose above 1400/100 ml during corticosteroid treatment, the .SIGMA.IRI values decreased and entered into Zone A. After the cessation of corticosteroids in a few of these patients, the .SIGMA.IRI values recovered and reentered Zone C, concomitant with an improvement in glucose tolerance. Similar recovery of insulin response from Zone A to Zone C was also observed after the treatment of 2 obese diabetic patients. Patients with glucose intolerance due to extra-pancreatic causes may secrete insulin at a higher rate than normal so long as the FBG level remains < 120 mg/100 ml, but a further deterioration in glucose metabolism may lead to a failure of insulin secretory mechanisms.