GALANIN REGULATES BASAL AND ESTROGEN-STIMULATED LACTOTROPH FUNCTION

OESTROGEN, an essential physiological regulator of reproductive functi on1, controls lactotroph proliferation and prolactin release2. The neu ropeptide galanin co-localizes to the lactotroph3, but its physiologic al function is largely unknown. Pituitary galanin expression is extrem ely sensitive to the oestrogen status of the animal. A marked elevatio n occurs during pregnancy and lactation 4, and exogenous 17beta-oestra diol can cause a 4,000-fold increase in messenger RNA levels5. Here we report that galanin is secreted by a minority of lactotrophs and is e ssential for the regulation of basal and vasoactive-intestinal-polypep tide-stimulated prolactin release. Hyperoestrogenization increases the number of galanin-secreting cells and the resulting increase in basal prolactin release is completely abolished by treatment with galanin a ntiserum. Galanin is a potent lactotroph growth factor and galanin-imm unoneutralization completely inhibits the previously reported6-8 mitog enic effects of oestrogen on the lactotroph. These findings represent direct evidence for paracrine regulation of lactotroph function and de monstrate that the effect of oestrogen on lactotroph proliferation and prolactin release are mediated by locally secreted galanin.