Effects of triiodothyronine and thyroxine on thyrotropin and prolactin secretion from bovine pituitary cells in vitro.

Abstract

Experiments were conducted to compare effects of thyroid hormones on basal and TRH-induced TSH and PRL release and production in vitro. TRH induced a linear increase (P < 0.001) in TSH and PRL release from bovine pituitary cells; TSH and PRL release increased 44% and 64%, respectively, for every 10-fold increase in TRH concentration. T3 at 0, 0.1, 1, and 10 ng/ml reduced the basal secretion of TSH 19%, 25%, and 25% and that of PRL 15%, 24%, and 37%. T3 did not alter the doseresponse slope of TRH-induced TSH and PRL release. However, for any given concentration of TRH, the amount of TSH and PRL released in the presence of T3 was less (P < 0.01) than the comparable control value. In addition to causing TSH and PRL release, TRH also induced a linear increase in total hormone production (cells plus medium); every 10-fold increase in TRH increased TSH and PRL production 13% and 20%, respectively. T3 completely blocked this TRH-mediated increase in TSH production but had no effect on the TRH-mediated increase i...