Relationship between Estradiol, Ergocryptine, and Thyroid Hormone: Effects on Prolactin Synthesis and Prolactin Messenger Ribonucleic Acid Levels*

Abstract

The effects of combinations of estradiol, ergocryptine, and T3 on PRL synthesis and PRL mRNA levels in monolayer cultures of pituitary cells have been investigated. Incubation of pituitary cells with [35S]methionine, followed by analysis of the newly synthesized proteins on a polyacrylamide gel, suggested that estradiol blocked the ability of ergocryptine to inhibit PRL synthesis, but that estradiol did not affect the ability of T3 to inhibit PRL synthesis. Quantitative studies utilizing immunoprecipitation of newly synthesized PRL demonstrated that PRL synthesis was reduced to 52% of control in ergocryptine-treated cells and returned to 83% of control in cells treated with ergocryptine plus estradiol. In the same experiment, T3 treatment reduced PRL synthesis to 50% of control, and PRL synthesis remained at 50% of control values after treatment with T3 plus estradiol. A concentration of 0.1 nM T3, which had little effect by itself, augmented the ability of ergocryptine to inhibit PRL synthesis, even in t...