Insulin secretory response to oral glucose load, diabetic microangiopathy and diabetic control: a study in non-insulin dependent diabetics.

To study the importance of the residual insulin secretion for the degree of diabetic control and for the development of microangiopathy 55 patients with non-insulin-dependent diabetes mellitus (NIDDM) were studied. A 1 hr oral glucose tolerance test was performed at diagnosis and 5-10 yr later. At diagnosis all patients were free of microangiopathy, at reassessment 24 patients had evidence of microangiopathy, i.e. retinopathy, neuropathy or nephropathy, alone or in combination. The glucose induced increments of insulin levels (delta IRI) at reassessment correlated inversely with the degree of diabetic control, measured by Haemoglobin A1 (r = -0.466, p less than 0.01), and with the mean fasting blood glucose throughout the follow up period (r = -0.491, p less than 0.01). delta IRI at diagnosis was similar in patients with and without microangiopathy, and at reassessment, although lower in the microangiopathy group (11.2 +/- 2.1 vs. 16.4 +/- 2.1 microunits/ml, p less than 0.1). The difference between the 2 groups did not reach statistical significance. When patients were separated into those treated with diet alone and those treated with oral antidiabetic agents, delta IRI at reassessment was significantly lower in patients on oral agents (10.5 +/- 1.9 vs. 17.2 +/- 2.2 microunits ml, p less than 0.01), but the prevalence of microangiopathy was not different between 2 groups (37% and 52%, respectively). These findings show that in patients with NIDDM the residual beta cell function is important for the degree of diabetic control, but a direct relationship between the degree of insulin deficiency and the presence of diabetic microangiopathy is not established.