Catecholamine Inhibition of Prolactin Secretion by Isolated Rat Adenohypophyses¹

Abstract

Rat adenohypophyses were incubated in medium 199 containing l-14C-glycine or a Krebs-Ringer-bicarbonate solution with glucose and a mixture of essential and non-essential amino acids. Dialyzed medium and anterior pituitary homogenates were elect rophoresed on polyacrylamide gel. After staining with Amido Black, the growth hormone and prolactin bands were quantified by microdensitometry and cut from the gel column for measurement of radioactivity. Growth hormone and prolactin contained in the medium were also measured by radioimmunoassay techniques. Epinephrine and norepinephrine inhibited prolactin release into the medium and this was associated with a proportionate rise in anterior pituitary prolactin. The catecholamines decreased total radioactive glycine incorporated into medium and pituitary prolactin but after 4 hr of incubation this decrease was not statistically significant. Inhibition of prolactin release occurred with concentrations of .5 μg/ml or greater of norepinephrine, and 1 μg/ml or greater of epinephrine. The catecholamines had no significant effect on growth hormone release. Both propranolol and phentolamine, at a concentration of 10 μg/ml, reversed in part, or wholly, the inhibitory effect of .5 μg/ml of norepinephrine. The effect of the 2 adrenergic blocking agents at a concentration of 10 μg /ml each, when used together, was additive. It is concluded that catecholamines are potent inhibitors of prolactin release in vitro. This action appears to be one which primarily involves release of prolactin, with effects on synthesis being secondary. The action of norepinephrine cannot readily be classified as to its receptor site activity. (Endocrinology86: 120, 1970)