Influence of Norepinephrine and Catecholamine-Depleting Agents on the Synthesis and Release of Prolactin and Growth Hormone

The in vitro incorporation of leucine- 4,5-3H into rat pituitary glands and its subsequent release into the incubation medium were studied. Quantitation of prolactin and growth hormone was by measurement of intensity of the bands obtained with the polyacrylamide gel technique without bioassay. Most of this newly synthesized prolactin is released into the medium and not retained within the gland. The addition of norepinephrine (10^-6M) caused a 70–85% decrease in the amount of radioactive prolactin released by the gland during a 7-hr incubation. An accumulation of labeled prolactin occurred in the treated glands, indicating the primary action of norepinephrine was to decrease prolactin release. The accumulation, however, was not proportional to the degree of inhibition of release, indicating that prolactin synthesis was secondarily inhibited. An increase in the radioactive prolactin in the gland was detectable 30 min afterthe addition of norepinephrine and was statistically significant 30 min later. Similar results were produced by epinephrine; however, metanephrine and other metabolites of catecholamine were completely inactive at 10^-5M. Injection of reserpine and α-methyltyrosine caused a large increase in the amount of radioactive prolactin released into the medium. The in vitro addition of reserpine, however, produced a profound decrease in the amount of prolactin released into the medium and caused an accumulation in the gland in the same manner as norepinephrine. Tyramine, in vitro, produced similar but less striking effects. Throughout these studies a careful record was maintained of the effect of catecholamines and their tissue-depleting agents, e.g., reserpine, on growth hormone synthesis and release. None of these treatments had any effect on growth hormone synthesis or release. (Endocrinology85: 916, 1969)