Stimulatory and inhibitory effects of neuropeptide Y on growth hormone secretion in acromegaly in vivo.

Abstract

It has been reported that neuropeptide Y (NPY) affects growth hormone (GH) secretion in several animal species. With respect to the role of NPY in regulating GH release in humans, one previous study has reported that NPY inhibited GH secretion from cultured GH-secreting pituitary adenoma cells in vitro. However, since it has yet to be explored whether NPY affects GH secretion in acromegaly in vivo, in this study we attempted to examine the effect of intravenous (i.v.) bolus injection of 100 microg of human NPY on plasma GH levels in 15 patients with active acromegaly, trying to find a possible correlation among GH responses to NPY, thyrotropin-releasing hormone (TRH;500 microg, i.v.), luteinizing hormone-releasing hormone (LHRH;100 microg, i.v.), and bromocriptine (Br;2.5 mg, per os). NPY significantly increased GH secretion (more than twice the basal level) in 4 (27%) patients, and all of them were responsive to LHRH and non-responsive to Br. In contrast, 3 (20%) acromegalics showed a significant decrease in GH levels (less than half the baseline) after NPY, and all these patients were responsive to both TRH and Br. From these results, we hypothesize that the NPY-induced increase in GH release may be a feature of somatotroph-like pituitary adenoma causing acromegaly, whereas the NPY-induced decrease in GH secretion may be a feature of lactotroph-like adenoma.