Modulation of prolactin release by altered levels of thyroid hormones

Abstract

In an attempt to delineate the effect of thyroid hormones on prolactin release, serum concentrations of prolactin in response to synthetic thyrotropin-releasing hormone (TRH) administration in subjects with normal and altered levels of thyroid hormones were determined by a heterologous radioimmunoassay for human prolactin. In 16 male and 19 female control subjects, an intravenous administration of TRH elicited a definite elevation in prolactin levels having a peak at 15 min after injection. This response of prolactin was markedly attenuated in all of the ten untreated hyperthyroid patients but was restored in eight subjects after the treatment. In contrast, TRH-mediated prolactin release was enhanced in most cases of primary hypothyroidism. Replacement of thyroid hormones in these patients resulted in a decrease in prolactin response to TRH. Treatment of six euthyroid subjects with triiodothyronine, on the other hand, unequivocally suppressed the release of prolactin. These results suggest that thyroid hormones per se are responsible for the blunted response of prolactin secretion to TRH administration.