Failure of Growth Hormone-Suppressing Agents to Affect TSH-Releasing Hormone- and LH-Releasing Hormone-Induced Growth Hormone Release in Acromegaly*

Abstract

In patients with acromegaly whose basal plasma GH [growth hormone] levels were suppressed with 9 mg/day of dexamethasone for 2 days, TRH [thyrotropin-releasing hormone]-(6 cases) and LHRH [luteinizing hormone-releasing hormone] (1 case) induced GH release were unaffected when the responses were compared to the basal levels. Phentolamine infusion, 70 mg in 150 min, or hyperglycemia induced by i.v. infusion of 700 ml of 50% glucose solution, did not suppress TRH-induced GH release in 2 acromegalic patients whose basal GH levels were lowered with these agents alone. Dexamethasone apparently does not affect TRH- or LHRH-induced GH release per se, but affects the basal state which determines the absolute level of response. TRH and LHRH probably act directly on pituitary tumor cells to release GH in acromegaly.