Simultaneous presence of estrogen receptors and gonadotropin-releasing hormone in the hypothalamus and of estrogen receptors and follicle-stimulating hormone in the pituitary of the fetal guinea pig.

Early studies in our laboratory have shown the presence of estrogen receptors (ER) in the fetal brain of guinea pig. Ontogenetic evaluation indicated maximal values of these specific binding sites between 50 and 62 days of gestation. We have now characterized ER in both the hypothalamus and the pituitary at the end of gestation. Autoradiographic studies after subcutaneous injection of [3H]estradiol to the fetus showed the nuclear localization of radioactivity in the hypothalamus to be in the neurons of the preoptic area and the nucleus arcuatus where gonadotropin-releasing hormone was also present. Nuclear localization of radioactivity also occurred in the anterior pituitary where the number of labeled cells increased from the border of the intermediate part to the periphery of the anterior lobe. These labeled cells were predominantly gonadotropes containing follicle-stimulating hormone. Since the fetal uterus responds very actively to estrogens, it is suggested that reciprocal influences of the hypothalamus-hypophyseal axis and gonadal steroid hormones are present in the fetal guinea pig.