Studies on Growth Hormone Secretion: I. Effects of Dibutyryl Cyclic AMP, Theophylline, Epinephrine, Ammonium Ion and Hypothalamic Extracts on the Release of Growth Hormone from Rat Anterior Pituitaries in Vitro

The release of immunoreactive growth hormone (GH) from male rat anterior pituitary explants was measured under a variety of experimental conditions. After a somewhat higher initial level, secretory rates remained essentially constant during a five-hour incubation period. Theophylline and dibutyryl cyclic AMP alone and in combination significantly stimulated GH secretion. Ammonium acetate and ammonium chloride (25 mM/L) also increased GH output by two-threefold. Unlike theophylline which increased both pituitary cyclic AMP levels and GH content of the medium, ammonium ion stimulated GH release was not accompanied by increased concentrations of intracellular cyclic AMP. Beef hypothalamic extracts, crude and purified, failed to stimulate GH release. Cerebral cortex extract and synthetic lysine vasopressin were also without effect. Epinephrine exhibited an inhibitory tendency on theophylline and cyclic AMP stimulated GH secretion. The results, which support the “second messenger” concept, are discussed in rel...