Rat anterior pituitary neuropeptides following chronic prolactin manipulation: a combined radioimmunoassay and mRNA study

Abstract

ABSTRACT Prolactin secretion is highly regulable, and the possibility exists that there are local intrapituitary factors controlling prolactin secretion. Recently, the neuropeptides vasoactive intestinal peptide (VIP), galanin and substance P (SP) have been co-localized to the lactotroph in the female rat. We investigated the effects of alterations in prolactin status in vivo on pituitary and hypothalamic expression of these peptides by specific radioimmunoassays and mRNA analysis. In the anterior pituitary, following haloperidol treatment, the contents of both VIP and galanin were suppressed to below detectable levels. Similarly, after bromocriptine treatment, the content of VIP was decreased to below the detection limit of the assay while galanin (14·2±1·3 vs control 21·0±2·1 fmol/mg, P < 0·05) also showed a significant reduction. The levels of VIP mRNA and galanin mRNA in these groups showed the same qualitative change as their respective peptides. Concurrent treatment with highdose oestrogen modified the VIP peptide response to bromocriptine (1368·7 ±149·2 vs bromocriptine 843·4±82·7 fmol/mg, P<0·05) but not to haloperidol. Oestrogen-induced decreases in galanin content were not influenced by either treatment. The pituitary content of SP showed a fall after oestrogen treatment (1·1±0·01 vs control 6·4±0·8 fmol/mg, P<0·05) which was not significantly altered by either bromocriptine or haloperidol. Likewise, SP mRNA levels in the pituitary were decreased by 90% following oestrogen treatment. Hypothalamic expression of these peptides did not change with any of the treatments. This study demonstrates the tissue and peptide specific influences of prolactin status in regulating anterior pituitary VIP, galanin and SP at the pretranslational level. The results of this study suggest that prolactin status and/or dopaminergic influences are important in the regulation of anterior pituitary neuropeptides. Journal of Endocrinology (1991) 131, 411–419