Biphasic Effect of Male Sex Hormone on the Pituitary of the Female Rat

Abstract

It is known that testosterone and testosterone propionate are capable of suppressing the cyclic activity of the ovaries in several species of animals. 1 2 3 4 Because rats which were treated with these substances presented ovaries with large corpora lutea, it was suggested that the androgenic hormones caused a release of the luteinizing principle from the anterior pituitary. This, in turn, gave rise to the persistent corpora lutea as in the diestrus of pregnancy or lactation. In monkeys and humans, on the other hand, similar treatment resulted in a cessation of ovulation and some degree of ovarian atrophy. This apparent species difference in the response to testosterone was also reflected in the uterus. The uteri of rats and rabbits developed progestation-like changes, 5 , 6 while the uteri of the primates underwent involution. 3 , 7

It seemed to us to be significant that Hertz and Meyer, 8 who used 1/10 to 1/20 of the amounts of testosterone propionate which had been employed by others to induce persistent corpora lutea, showed that these small doses effectively inhibited the secretion of the follicle-stimulating hormone in parabiotic rats. This suggested that a qualitative difference in pituitary response to large and small doses of androgen might account for the confusing variation in the results which had been obtained. The increasing clinical use of androgenic therapy for certain ovarian dysfunctions lent practical as well as theoretical importance to further investigation.

Groups of adult female rats, showing regular estrous cycles, were given daily subcutaneous injections of testosterone propionate for 16 clays. A different daily dose was used for each group, and vaginal smears were made on each animal every day. In the groups of rats receiving 1.0 mg and 0.1 mg per day vaginal cornification was completely suppressed throug∗hout the injection period.