The Androgen-Sterilized Rat: Induction of Ovulation and Implantation by Luteinizing Hormone-Releasing Hormone

Abstract

Androgen treatment of newborn female rats results in persistent vaginal cornification and anovulation, a condition also associated with hypothalamic disorders. Studies were designed to extend previously reported observations that LHRH [luteinizing hormone releasing hormone] will induce ovulation in these animals. A single injection of 25 nmol/kg LHRH induced a single estrous cycle, as judged by vaginal cytology, but subsequent LHRH injections were required at the end of each cycle to induce additional estrous cycles. Injections of LHRH induced ovulation; furthermore, the ovulation rate increased with subsequent treatments of LHRH, indicating a priming effect by the initial injection. Whereas only 1 out of 40 control rats mated, 8 of 43 LHRH-treated rats mated on the 1st day of cohabitation. In this initial study, mated animals were autopsied on days 14-15 and no pregnancies had occurred. In other studies, normal fertilized eggs were recovered on the 1st and 2nd day after mating in LHRH-treated sterile rats. Furthermore, some embryos had developed normally to the blastocyst stage by day 5, but all were degenerating by day 6. When day 5 embryos from androgen-sterilized females treated with LHRH to induce ovulation were transferred into the uterus of normal pseudopregnant female rats, normal implantation occurred, indicating that the embryos possessed normal embryonic competence. Histological evaluation of corpora lutea and the uteri plus RIA [radioimmunoassay] analysis of serum progesterone in these pregnant androgen-sterilized rats demonstrated a deficit of the hormone. In subsequent studies, the administration of either exogenous progesterone or PRL, or the transplantation of normal pituitary glands into the renal capsules of experimental animals allowed normal implantation and maintenance of pregnancy to occur.