Galanin is an estrogen-inducible, secretory product of the rat anterior pituitary.

Galanin is a peptide widely distributed throughout vertebrate central and peripheral nervous systems. Although its precise physiologic role is unknown, it can stimulate the pituitary secretion of prolactin and growth hormone. We examined the control of rat galanin (rGal) gene expression in the anterior pituitary using RNA blot and in situ hybridization analyses and using specific RIA. Pituitaries of normal male and ovariectomized female rats contained little detectable rGal mRNA. Treatment of these animals with 17 beta-estradiol increased pituitary rGal mRNA up to 4000-fold. These increases depended on time and dose of estrogen administration and correlated with up to 50-fold increases in pituitary galanin-like immunoreactivity. Galanin-like immunoreactivity was detectable in the plasma of estrogen-treated animals. Pituitary levels of rGal mRNA in female rats varied greater than 30-fold during the estrous cycle, with a peak on estrus and a nadir on diestrus. Estrogen-induced rGal gene expression was also observed in transplantable MtTW15 prolactin- and growth hormone-containing tumors but not in neuronal tissues expressing this gene. These data demonstrate that rGal is a secreted product of rat anterior pituitary cells, where its gene expression is strongly affected by physiologic levels of circulating estrogen.