Preliminary Studies of Plasma Growth Hormone Releasing Activity during Medical Therapy of Acromegaly

Abstract

The in vitro growth hormone releasing activity of plasma obtained from six acromegalic subjects was measured before and during therapy. In five subjects, plasmas were obtained before and during successful medical therapy with medroxyprogesterone acetate (MPA). The sixth subject was sampled before and after transphenoidal Sr⁹⁰-induced hypopituitarism. All subjects had a decrement in fasting growth hormone levels with respective therapies (29-88%).

The in vitro growth hormone released from Rhesus monkey anterior pituitaries was assessed after incubating one lateral half in control plasma (pre-therapy) and the contralateral pituitary half in plasma obtained during or after therapy. Studies with plasmas obtained from the five patients successfully treated with MPA showed a decrease in growth hormone releasing activity during therapy in all (18-57%). Plasma obtained after Sr⁹⁰ pituitary ablation in the sixth subject had 35% more growth hormone releasing activity than obtained before therapy.

These results suggest that active acromegalics who respond to MPA with significantly lowered growth hormone levels may actually achieve this response because of a decrease in growth hormone releasing factor measured peripherally. The opposite response in one acromegalic subject, following Sr⁹⁰ pituitary ablation and hypopituitarism, suggests that growth hormone releasing factor secretion may increase when growth hormone levels are lowered by ablative therapy.

Key words

Plasma Growth Hormone - Therapy of Acromegaly - Medroxyprogesterone Acetate (MPA)

1 Present address: Department of Medicine, The Medical College of Wisconsin, Wood Veterans Administration Center, Milwaukee, Wisconsin

2 Present address: Department of Medicine, Loyola University Stritch School of Medicine, and Research Service, Hines Veterans Administration Hospital, Maywood, Illinois