TRF and Thyroid Hormones on Prolactin Secretion By Rat Anterior Pituitary Cellsin Vitro1

The effect of pGlu-His-Pro-NH2 (TRF) on the secretion of prolactin (PRL) from rat anterior pituitary glands and cell cultures derived from normal and propylthiouracil (PTU)-fed rats is reported. TRF only slightly increased (less than 50% over control levels) the rate of secretion of radioimmunoassayable PRL or immune precipitated biosynthesized [3H]-PRL secreted by normal anterior pituitary cells, but had a greater effect on the rate of secretion of PRL by pituitary cell cultures obtained from PTU-treated rats. Furthermore, PTU-treated rats’ hemi-pituitary glands incubated in vitro also respond to TRF, demonstrating that the response to TRF by rat tissue is not a result of the cell dispersion or culture procedure. The administration of thyroid hormones which inhibit the TRF mediated secretion of TSH in vivo and in vitro suppress the secretion of PRL by hemi-pituitaries and dispersed cell cultures of anterior pituitaries from PTU-fed rats. Comparative studies of the [3H]-TRF binding to (mouse) TSH secreting vs (rat) PRL/GH secreting neoplastic cells revealed that the TRF binding constants and specificity of competition by several TRF analogues for [3H]- TRF binding were very close in both types of tumors, leading us to propose that the TRF receptors in PRL or TSH secreting cells are similar. (Endocrinology93: 26, 1973)