Androgen Sterilization Produced by Intracerebral Implants of Testosterone in Neonatal Female Rats

Abstract

To study the effects of intracerebral implantation of androgen in newborn female rats, 12 [mu]g paraffin pellets, each containing 3 or 1 [mu]g dissolved testosterone propionate (TP), were extruded bilaterally into the brain of 4-day-old female rats. Intact animals, rats receiving paraffin-TP pellets sc and rats with "blank" pellets devoid of TP in the brain served as controls. Rats treated with 10 [mu]g TP in oil sc were included as reference groups. Hypothalamic paraffin-TP pellets at both dose levels significantly advanced vaginal opening. Moreover, 16/19 rats receiving 6 fig testosterone and 16/20 receiving 2 fig testosterone in the brain showed persistent vaginal estrus (PVE); 8/16 in the latter group showed PVE within 12 days after vaginal opening, whereas 8 developed PVE from 37 to 60 days after opening. These differences in delay in onset of PVE appeared to be related to site of placement of the pellets in the hypothalamus. Similar pellets placed sc abolished vaginal cyclicity in 7/15 rats (6 [mu]g dose) and 4/10 rats (2 [mu]g dose). Eleven of the 16 rats which developed PVE following brain implantation of 2 [mu]g TP showed evidence of repeated acceptance of the male, as did 5/11 receiving 10 [mu]g TP in oil sc. Since the most striking effects of neonatal androgen treatment were obtained by placement of TP in the basal hypothalamus, these data are consistent with current concepts regarding the site of action of testosterone in producing androgen sterilization.