Pituitary Gonadotropic Inhibitory Activity of Various Steroids in Ovariectomized-Intact Female Rats in Parabiosis

Abstract

Summary Steroids of the ring A phenolic group, or derivatives thereof, have been studied for their ability to inhibit biosynthe-ses and/or secretion of pituitary gonadotro-pins and uterotropic activity by means of a method utilizing the intact female in para-biosis with an ovariectomized rat. Three hundredth μg of estradiol-17β was the smallest total dose to produce pituitary inhibition and 0.2 μg was the minimum dose to produce a maximum inhibition. The corresponding total doses of 0.2 and 0.9 μg of estradiol-17β were required to produce minimum uterine weight stimulation and the minimum dose to produce a maximum response, respectively. Four steroids showed significantly greater pituitary inhibition than utero-trophic activity; 17α-ethynylestra-1(10),5-di-ene-3β,17β-diol, A-homoandrosta-1,4,5 (10)-triene-3, 17-dione, 3 -methoxyestra-1,3,5(10)-triene-17β-cyanethoxy and 17β-hydroxy-A-homoandrosta-1(10),2,4a-trien-4-one.