Growth Hormone Releasing Hormone-Sensitive Adenylate Cyclase Activity in Growth Hormone-Producing Pituitary Adenoma: Correlation to the Response of Plasma Growth Hormone to Growth Hormone Releasing Hormone in Patients with Acromegaly.

Abstract

The correlation between response of plasma GH to GHRH and the GHRH-induced stimulation of the intracellular adenylate cyclase (AC) activity in pituitary adenoma cell membranes in acromegalic patients was investigated. Each peak plasma GH level after iv administration of GHRH ranged from 1.1 to 13.8 times the basal level in 13 acromegalic patients. On the other hand, the maximal stimulation of intracellular AC activity (cAMP production) induced by GHRH varied from 1.4 to 6.4 times the control level in each GH-producing pituitary adenoma cell membrane. A significant positive correlation (r = 0.89, P less than 0.005) between plasma GH response to GHRH and intracellular cAMP production stimulated by GHRH was observed in nine of the acromegalic patients. In contrast, the response of plasma GH to GHRH was significantly blunted, despite a fairly large production of intracellular cAMP stimulated by GHRH, in the other four acromegalic patients. These results suggest that GHRH-induced GH release from GH-producing pituitary adenomas of patients with acromegaly may be regulated not only by GHRH receptor-adenylate cyclase system but also modified by several other factors including somatostatin and Sm-C.