Estrogen regulation and localization of galanin gene expression in the rat uterus

To determine whether galanin is a target for estrogenic regulation in the rat uterus, we measured the effects of estrogen on galanin mRNA expression in the uterus of ovariectomized rats and compared the results with the regulation of galanin in the anterior pituitary. Treatment of the animals with a single dose of 17 beta-estradiol resulted in a rapid transient increase of galanin mRNA, similar to that in the pituitary of the same animals, with a peak at 3 h after stimulation and a return to prestimulation levels after 24 h. No galanin mRNA was detected in ovariectomized control animals in either tissue. By in situ hybridization of rat uterus 3 h after estrogen stimulation, we found that galanin mRNA was localized in the endometrium in stromal cells that are close to the lumen. There was no hybridization in the myometrium of the estrogen-treated animals. Surprisingly, and strikingly different from results in the pituitary, in the uterus with a constant and prolonged exposure to estrogen by diethylstilbestrol (DES) implants, the induction of galanin mRNA was only transient, with return to baseline levels by 24 h despite the continued presence of DES. On the other hand, in the pituitary there was a rapid and sustained increase of galanin mRNA. These data demonstrate that 1) one of the initial steps in the mechanism of estrogen stimulation in the rat uterus involves galanin gene expression; 2) in the uterus galanin mRNA is expressed in stromal cells of the endometrium; and 3) the regulation of galanin mRNA expression by estrogen in the pituitary and the uterus is markedly different.