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 ex pression in the uterus of ovariectomized rats and compared the results with the regulation of galanin in the anterior pituitary. Treatment o f the animals with a single dose of 17beta-estradiol resulted in a rap id transient increase of galanin mRNA, similar to that in the pituitar y of the same animals, with a peak at 3 h after stimulation and a retu rn to prestimulation levels after 24 h. No galanin mRNA was detected i n ovariectomized control animals in either tissue. By in situ hybridiz ation of rat uterus 3 h after estrogen stimulation, we found that gala nin mRNA was localized in the endometrium in stromal cells that are cl ose 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 inducti on 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 t he pituitary there was a rapid and sustained increase of galanin mRNA. These data demonstrate that 1) one of the initial steps in the mechan ism of estrogen stimulation in the rat uterus involves galanin gene ex pression; 2) in the uterus galanin mRNA is expressed in stromal cells of the endometrium; and 3) the regulation of galanin mRNA expression b y estrogen in the pituitary and the uterus is markedly different.