Changes in insulin resistance with long-term insulin therapy.

Thirteen newly diagnosed diabetic subjects, 5 with insulin-dependent diabetes mellitus (IDDM) and 8 with non-insulin-dependent diabetes mellitus, mean age 37.1 yr (range 25-64 yr), underwent glucose-clamp studies at diagnosis of diabetes at plasma glucose 200 mg/dl. Each subject was then treated twice daily with insulin for 6 mo with improvement in glycemic control, and the glucose-clamp studies repeated. Changes in glucose uptake at an insulin infusion rate of 1.0 mU X kg-1 X min-1 varied greatly from diagnosis to 6 mo. There were significant negative correlations between change in glucose uptake and diabetes type (r = -.78, P less than .002), C-peptide secretion (r = -.66, P less than .05), and age (r = -.62, P less than .05). At an insulin infusion rate of 10 mU X kg-1 X min-1 there was improvement in glucose uptake from diagnosis to 6 mo that did not reach statistical significance. During the steady-state periods of the glucose-clamp studies at diagnosis, growth hormone (GH) rose above basal, which reached statistical significance at the higher insulin infusion rate. This increase in GH was not apparent at the time of the glucose-clamp studies after insulin therapy. Our results indicate that in the clinical situation, only patients with IDDM can expect an improvement in their sensitivity to physiologic insulin levels with long-term insulin therapy. In all subjects, improvement in glycemic control leads to abolition of GH secretion in the presence of hyperglycemia.