FUNCTION OF GALANIN IN THE ANTERIOR-PITUITARY OF ESTROGEN-TREATED FISCHER-344 RATS - AUTOCRINE AND PARACRINE REGULATION OF PROLACTIN SECRETION

Estrogen is a robust stimulator of galanin synthesis and secretion in the anterior pituitary. Galanin is colocalized in lactotrophs in the e strogen-treated anterior pituitary, and its roles in lactotroph functi on are still being elucidated. Ln the present studies, Ne quantified t he phenotypes of estrogen-treated Fischer 344 rat anterior pituitary c ells expressing the galanin gene by dual in situ hybridization. The to tal population of galanin-positive pituitary cells increased from unde tectable levels to 16% of all cells after 2 weeks of estrogen treatmen t. More than 90% of the galanin-positive cells coexpressed PRL messeng er RNA, and one-third of the lactotrophs expressed galanin messenger R NA. We hypothesized that galanin in the anterior pituitary may contrib ute to the heterogeneous secretion of PRL, and that one of the functio ns of galanin is to regulate PRL secretion in an autocrine/paracrine m anner. To test this hypothesis, we performed the reverse hemolytic pla que assay combined with in situ hybridization to measure PRL secretion and galanin gene expression within the same individual cells. PRL, se cretion from galanin-positive lactotrophs was significantly greater th an that from galanin-negative lactotrophs. Moreover, treatment with ga lanin antiserum significantly attenuated PRL secretion from galanin-po sitive cells, and treatment with galanin significantly enhanced PRL se cretion from galanin-negative lactotrophs. In conclusion, these data p rovide direct evidence that galanin derived from the estrogen-treated anterior pituitary stimulates PRL secretion in both autocrine and para crine manners.