Comparison of the Effect of Hypothalamic and Pituitary Implants of Estrogen and Testosterone on Reproductive System and Adrenal of Female Rats

Abstract

Implants of estradiol in either the median eminence or in the anterior pituitary of female rats evoked a pseudopregnancy-like syndrome characterized by persistent diestrus, mammary development and secretion, a tendency to reduction in ovarian and uterine weight and enlargement of the anterior pituitary gland. These effects appeared to be mediated centrally rather than by systemic absorbtion of estrogen since systemic administration of estradiol produced uterine enlargement rather than the reduction of this organ. Implants of testosterone in the median eminence were followed by a reduction in uterine and ovarian weight, but the estrous cycle was only slightly disturbed, and there was no mammary development or putiitary enlargement such as that observed with estrogen implants. Testosterone implants in the anterior pituitary were without effect. No adrenal enlargement was found in female rats with implants of either testosterone or estrogen, which was in contrast to earlier results with similar implants of these steroids in the hypothalamus of male rats in which adrenal enlargement was observed. Estrogen can act centrally on the hypothalamus and anterior pituitary to evoke release of prolactin and to inhibit release of gonadotropins in female rats, whereas testosterone appeared to be effective in inhibiting gonadotropin release without producing a detectable alteration in prolactin discharge.