Anti-ovulatory/anti-pregnancy effects of (D-Phe2)-LRH analogs administered early in the rat estrous cycle

Suppression of ovulation in the rat by an orally active antagonist of luteinizing hormone-releasing hormone

A synthetic antagonist of luteinizing hormone-releasing hormone blocked ovulation in rats in a dose-dependent manner when given by gavage on the afternoon of proestrus. Ovulation was delayed for at least 1 day in all animals given 2 milligrams of antogonist and in some of the animals treated with 1 or 0.5 milligram. Oral administration of 2 milligrams also blocked the preovulatory surge of luteinizing hormone. This demonstration that antagonists of luteinizing hormone-releasing hormone can have oral antiovulatory activity clearly enhances their therapeutic potential.

Inhibition of preovulatory gonadotropin secretion in the rhesus monkey by [(<Glu-Pro)1,D-Phe2,D-Trp3,6]-LHRH

We report the first example of a complete inhibition of preovulatory gonadotropin secretion resulting from administration of a luteinizing hormone releasing hormone antagonist during a spontaneous menstrual cycle. The antagonist, [(<Glu-Pro)1,D-Phe2,D-Trp3,6]-LHRH, was administered to a rhesus monkey beginning on Day 9 of the menstrual cycle; ovulation did not occur and preovulatory peaks of LH and FSH were not observed despite elevations in serum estradiol-17 beta of sufficient strength and duration to elicit gonadotropin surges. Midcycle gonadotropin surges had already commenced in another monkey, however the antagonist did partially inhibit LH and FSH secretion although ovulation and luteinization were not prevented. Normal hormone secretion patterns and luteal function were observed in another monkey when the antagonist was given after the midcycle FSH and LH peaks had already occurred. These data emphasize the importance of beginning treatment with LHRH antagonists early in the follicular phase of the menstrual cycle.

Ovulation inhibition by daily i.m. administration of a highly active LH-RH analog (d-ser(TBU)6-LH-RH-(1-9)-nonapeptide-ethylamide)

A highly active LH-RH-analog (D-Ser(TBU)6-LH-RH-(1-9)-nonapeptide-ethylamide = HOE 766) was administered to normally cyclic and ovulatory women in a double-blind study. Each woman received from day 1 through day 14 of the cycle according to a randomization plan either 10 microgram HOE 766 i.m. or a placebo. Ovulation was inhibited for at least two weeks in all subjects receiving HOE 766. The initially very marked release of LH measured 4 hourse after the injection decreased within 3 days by approximately 50%, and remained at this level for the remainder of the experiment while the initially high FSH response was abolished during further treatment. In 3 out of 5 women receiving the analog, serum estradiol was severely suppressed, in the remaining 2 slightly. Within 5 days after the discontinuation of treatment, the pituitary had regained the capacity to respond normally to LH-RH. It is postulated that follicular maturation is disturbed by the unphysiologic pattern of gonadotropin secretion during administration of HOE 766.

Peptide contraception: antifertility properties of LH-RH analogues

A prototype LH-RH antagonist dampened the proestrous gonadotropin surge and blocked ovulation but had no effect on pregnant animals. In contrast, LH-RH and two highly potent LH-RH agonists terminated pregnancy when administrated prior to or following implantation. This contragestational effect, as well as other antireproductive properties of the agonists, coupled with the reversibility of their effects, strongly suggest that peptides may provide a new basis for contraception.

Effect of an LH-RH antagonist on reproductive status of immature female rats

Administration of the LH-RH antagonist, D-Phe2-D-Ala6-LH-RH (Wy-18, 185) to immature female rats from days 25--35 of age was without significant effect on day of vaginal opening (puberal onset), weights of the ovaries, uteri and anterior pituitary, and on ovarian histology on autopsy day 39.