Effect of ovariectomy and clomiphene on the in-vitro incorporation of [3H]thymidine into pituitary DNA and on prolactin synthesis and release in rats

Abstract

In the anterior pituitary gland changes in prolactin synthesis and in the incorporation of [3H]thymidine into DNA are coincident under several experimental conditions. We investigated whether these changes are obligatory, thus indicating a regulatory mechanism common to the synthesis of both macromolecules. Alternatively, the parallel changes may represent similar responses to various stimuli operating through different pathways. The administration of alpha-methyl-p-tyrosine (alpha MpT) to rats stimulated the incorporation of [3H]leucine into prolactin and [3H]thymidine into DNA. When the effectiveness of oestrogen was suppressed by ovariectomy or by blockage of oestrogen receptors by the antioestrogen clomiphene, alpha MpT stimulated the synthesis of prolactin but not the incorporation of [3H]thymidine into pituitary DNA. The results clearly indicate two independent mechanisms regulating the synthesis of prolactin and DNA in the anterior pituitary gland.