Evidence for a central abnormality in the regulation of growth hormone secretion in insulin-dependent diabetes.

To assess pituitary and hypothalamic function in diabetes, 100 micrograms growth hormone releasing factor 1-44 was administered to 10 normal subjects at fasting plasma glucose (5.2 +/- 0.1 mmol/l, mean +/- S.E.M.), 10 insulin-dependent diabetics while euglycaemic (6.4 +/- 0.3 mmol/l), and 10 while hyperglycaemic (13.1 +/- 1.3 mmol/l). Six of the diabetics participated in both parts of the study. The normal subjects and euglycaemic diabetics produced similar peaks in growth hormone (118.2 +/- 37.6 vs 105.2 +/- 23.9 mU/l, p = 0.69). The peak growth hormone level was reached between 30 and 45 minutes in all the normal subjects, but varied between 15 and 75 minutes in the diabetics. While all normal subjects suppress their growth hormone response to releasing factor when hyperglycaemic, not all the diabetics did so, and the suppression did not reach statistical significance on comparison of euglycaemic and hyperglycaemic diabetics (105.2 +/- 23.9 vs 64.7 +/- 19.4 mU/l, p = 0.2). Comparison of results from those diabetics studied at both euglycaemia and hyperglycaemia again showed no significant difference (140.8 +/- 30.9 vs 90.2 +/- 27.7 mU/l, p = 0.22). These results suggest a central, possibly hypothalamic, abnormality to account for the disruption of growth hormone regulation in diabetes.