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Estradiol Induces Expression of 5-Hydroxytryptamine (5-HT) 4, 5-HT5, and 5-HT6 Receptor Messenger Ribonucleic Acid in Rat Anterior Pituitary Cell Aggregates and Allows Prolactin Release via the 5-HT4 Receptor

Laboratory of Cell Pharmacology, University of Leuven, Medical School, Campus Gasthuisberg, B3000 Leuven, Belgium

Address all correspondence and requests for reprints to: Prof. Carl Denef, Laboratory of Cell Pharmacology, University of Leuven, Medical School, Campus Gasthuisberg (O & N), B-3000 Leuven, Belgium. E-mail: Carl.Denef{at}med.kuleuven.be.

Serotonin [5-hydroxytryptamine (5-HT)] is known to control prolactin (PRL) release at a hypothalamic level, but a pituitary site of action remains poorly studied. The present study explores the acute effect of 5-HT on PRL release in rat anterior pituitary aggregate cell cultures, the influence of steroid and thyroid hormones, and the 5-HT receptor (5-HTR) subtype(s) involved. 5-HT elicited a prompt increase in basal PRL release, an effect strongly potentiated by estradiol (E₂) in the culture medium (dose response 1–100 nM). In E₂ condition, the PRL response was not affected by the nonselective 5-HTR antagonists methysergide and methiothepin nor by 5-HTR1, 5-HTR2, 5-HTR3, 5-HTR6, and 5-HTR7/5 antagonists, but was fully blocked by the 5-HTR4 antagonist GR 113808. Among various agonist analogs, only the 5-HTR4 agonist cisapride and the 5-HTR2 agonist -methyl-5-HT evoked PRL release. The effect of -methyl-5-HT also required E₂ during culture and was abolished by GR 113808 but not by combined 5-HTR2A, B, and C blockade. In E₂-treated aggregates, 5-HT caused a 5-fold increase in cAMP levels. The intact anterior pituitary expressed mRNA of all known members of the 5-HTR family. In aggregates, 5-HTR4, 5-HTR5, and 5-HTR6 mRNA expression required E₂ during culture. The effect of 5-HT on PRL release was not affected by blocking the serotonin transporter or the vesicular monoamine transporter. The present data suggest a widespread expression of 5-HTRs in the rat anterior pituitary, several of which are up-regulated by estrogen, and that, in the presence of estrogen, one of these, the 5-HTR4, mediates acute PRL release.

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