THE HIGHER THE GROWTH HORMONE RESPONSE TO GROWTH HORMONE RELEASING HORMONE THE LOWER THE RESPONSE TO BROMOCRIPTINE AND THYROTROPHIN RELEASING HORMONE IN ACROMEGALY

In acromegaly a direct relationship has been demonstrated between GH responsiveness to TRH and to the dopaminergic agent bromocriptine (Br). Recent data show an inverse relationship between GH responsiveness to Br and to GH releasing hormone (GHRH), but not between the GH responses to GHRH and TRH. Thirty-one acromegalic patients, 18 women and 13 men (age 46.2 +/- (SD) 13 years) were studied. Four patients had been treated, but all still had active disease. The GH responses to GHRH (hpGHRH1-44, Bachem 100 micrograms i.v. bolus), TRH (Thyroliberin, Hoechst 200 micrograms i.v. bolus) and Br (Parlodel 5 mg orally) were assessed in most of the patients. The GH responses to GHRH showed a wide interindividual variation (delta GH 1-995 ng/ml), which correlated significantly with the basal GH levels (r = +0.85, P less than 0.0001, n = 31). GH increments in response to GHRH were inversely related to the responses to Br, i.e. the lower the GH increase after GHRH the greater the GH decrease after Br (r = -0.49, P less than 0.01, n = 30). This decrease correlated with the basal PRL level (r = +0.45, P less than 0.02, n = 29) and also the GH response to TRH (r = +0.66, P less than 0.0001, n = 30). An inverse correlation was also found between the GH responses to TRH and to GHRH (r = -0.43, P less than 0.02, n = 29). The data are consistent with the existence of GH-secreting adenomas which are more sensitive to GHRH and less to Br and TRH (pure somatotroph adenomas) and of mixed (lactotroph-like adenomas) responsive to TRH and Br but less responsive to GHRH.