Effect of glucose on the growth hormone response to L-dopa in normal and diabetic subjects.

The effect of hyperglycemia on the growth hormone response to oral L-dopa (500 mg.) was assessed in eight normal and eight insulin-dependent diabetic subjects. A peak growth hormone response of 21.0 +/- 4.0 ng./ml. (mean +/- S.E.M.), significantly above baseline (p less than 0.01), was achieved in the normal group following oral L-dopa. Glucose concentrations did not change and were approximately 80 mg./100 ml. throughout. Administration of 100 gm. oral glucose with the L-dopa, or thirty minutes thereafter, totally suppressed the growth hormone response in all eight and six of the subjects, respectively. A peak growth hormone response of 20.0 "/- 1.7 ng./ml. (mean +/- S.E.M.), significantly above baseline (p less than 0.001), was obtained in eight nonobese, insulin-dependent diabetics, in spite of prevailing hyperglycemia (mean plasma glucose 243-258 mg./100 ml.) throughout the test. Endogenous hyperglycemia was achieved in these patients by lessening the usual strict adherence to plasma glucose control for the purpose of the study. These results suggest an abnormality in the hypothalamus or pituitary of diabetic subjects allowing growth hormone responsiveness in spite of hyperglycemia.