Title: Effects of Triiodothyronine and Thyroxine on Thyrotropin and Prolactin Secretion from Bovine Pituitary Cells<i>in Vitro</i>*
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 in PRL production. In contrast to T3, T4 (10, 100, and 1000 ng/ml) had no effect on basal TSH and PRL release or production. However, T4 at 10 and 100 ng/ml increased dose-response slopes of TRH-induced TSH release 65% and 53% and those of TRH-induced PRL release 28% and 30%, respectively. Low levels of T4 (10 and 100 ng/ml) did not affect the TRH-mediated increase in TSH and PRL production, while T4 at 1000 ng/ml was inhibitory. Results of this study demonstrate that T3 and T4 differ markedly in terms of their effects on TSH and PRL release and production. On the other hand, for a given thyroid hormone, the effects on TSH and PRL secretion are remarkably similar. Hence, our results do not support the view that dissociation of TSH and PRL release in vivo results from thyroid hormones differentially affecting the ability of lactotrophs and thyrotrophs to respond to TRH.
Publication Year: 1981
Publication Date: 1981-01-01
Language: en
Type: article
Indexed In: ['crossref', 'pubmed']
Access and Citation
Cited By Count: 17
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