Administration of luteinizing hormone-releasing hormone analogs delays ovulation without affecting the luteal function in rhesus monkeys**Supported in part by a grant from the Ford Foundation; the Program for Applied Research on Fertility Regulation (PARFR), Northwestern University, and sub-agreement PARFR 302 (DPE-0546-A-00-1003-00); the National Institute of Health (SP30 HD 10202, Radioimmunoassay and Bioassay Cores); and The Moody Foundation

Effect of a gonadotropin-releasing hormone agonist and gonadotropins on ovarian follicles in cynomolgus monkey: a model for human ovarian hyperstimulation

STUDY OBJECTIVE

To examine the effect on large follicles (greater than or equal to 2 mm) of human menopausal gonadotropin (hMG) and buserelin acetate, a gonadotropin-releasing hormone agonist in monkeys.

DESIGN

Experimental.

SETTING

Reproductive research laboratory.

ANIMALS

Fourteen cyclic cynomolgus monkeys receiving hMG alone for 8 days or buserelin acetate plus 8 (group 1), 12 (group 2), or 16 (group 3) days of hMG administration always starting from day 1 of the cycle.

RESULTS

The different treatments were effective in over-riding the specific ovulatory quota of 1, and more large follicles developed in treatments involving long duration and higher doses of hMG. In buserelin acetate plus hMG treatments, the frequency of dissociated follicles and follicles in late atresia were, respectively, lower and higher than in hMG alone treatment. The numbers of recoverable mature oocytes (germinal vesicle breakdown) were similar to the numbers of such oocytes recovered after hyperstimulation performed for human in vitro fertilization and embryo transfer (IVF-ET). However, the number of mature oocytes enclosed in typically preovulatory follicles was very low because there were numerous dysmature follicles.

CONCLUSION

These data suggest a deleterious effect of buserelin acetate plus hMG treatments on the recruitable follicles at the time when treatments start. The implications of these observations in the field of human IVF-ET are discussed.

Inhibitory effects of treatment with an LHRH antagonist on the ovulatory cycle are reduced when administered during the late follicular phase

To compare the effects of transitory suppression of pituitary gonadotropin secretion by an LHRH antagonist at the mid or late follicular phase of the menstrual cycle, adult macaques with normal menstrual cycles were treated with an LHRH antagonist (N-Ac-D-Nal(2)1,D-pCl-Phe2,D-Trp3,D-hArg(Et2)6,D-Ala10 ]LHRH (detirelix) administered subcutaneously at a dose of 300 micrograms/kg, daily for 3 days beginning either during the mid or late follicular phase. In all eight animals treated during the mid follicular phase, serum concentrations of LH and FSH declined and remained suppressed for 4 days. This caused a fall in serum concentrations of estradiol and the expected ovulation failed to occur. During the recovery period a marked rise in serum FSH occurred followed by normal follicular development and ovulation 14.8 +/- 0.6 days after the last injection of antagonist. Of the 9 macaques given the same treatment during the late follicular phase, only in two was the expected rise in serum progesterone prevented. In 4 of the animals a transitory suppression in LH and estradiol was observed but this was followed by a recovery and occurrence of an LH surge and rise in serum progesterone indicating ovulation during the course of treatment. In the remaining 3 macaques treatment commenced on the day of the initiation of the LH surge and was associated with a progesterone rise of normal duration but lower than normal magnitude during the early luteal phase. These results show that LHRH antagonist treatment causes rapid inhibition of pituitary-ovarian function when administered up to the mid follicular phase of the cycle and is effective in blocking ovulation. The suppressive effects of the antagonist are reduced when administered during the late follicular phase. This may be due to decreased dependence of the pituitary gonadotrope on LHRH at this time and on decreased dependence of the dominant follicle on the gonadotropins.

The use of gonadotropin-releasing hormone analogs for in vitro fertilization: comparison between the standard form and long-acting formulation of D-Trp-6-luteinizing hormone-releasing hormone

The introduction of luteinizing hormone-releasing hormone (LH-RH) analogs into treatment schemes for the stimulation of ovulation has enabled the authors' in vitro fertilization (IVF) team to overcome two problems; they can now suppress spontaneous LH peaks and program their activity. Two hundred and five IVF cycles were investigated. The agent used was D-Trp-6-LH-RH, either in a sustained release formulation (112 cases, group 1) or in a standard form (93 cases, group 2). The quantity of human menopausal gonadotropin (hMG) necessary for adequate ovarian stimulation was much lower when the standard form of the analog was used. The number of oocytes recovered per puncture was greater in group 1 (7.6 compared with 5.1), but the difference was not significant when considering the number of embryos (2.4 compared with 2.1). The corrected pregnancy rate (with allowance for progressive introduction of freezing from the third embryo onwards) was identical in both groups. The authors conclude that systems in which LH-RH analogs are employed have a clear advantage over the classical treatment with clomiphene citrate/hMG, and that the immediate-action formulation of D-Trp-6-LH-RH is preferable.

Clinical applications of LHRH analogues

What is the current state of clinical application of inhibition of gonadal activity with LHRH agonists or antagonists? It seems unlikely in the short term that antagonists will be widely applied due to the short-acting nature of the present compounds and their troublesome side-effects. In contrast clinical studies with a number of agonists have demonstrated their efficacy in producing a hypogonadal state safely with rapid recovery following cessation of therapy. Although nasal administration may be suitable for short-term suppression (up to 28 days) it seems likely that long-acting depot preparations will be useful for more prolonged suppression. Perhaps the easiest application to determine will be the profound suppression required to produce medical castration in hormone-dependent tumours. The combination of agonist and receptor blocker is attractive particularly when the receptor blocker like cyproterone acetate also suppresses the release of LH, FSH and adrenocorticotrophic hormone. In cancer of the prostate and breast the side-effects due to inhibition of secretion of testosterone and oestradiol are tolerable although the only benefit over castration is the avoidance of minor surgery. The agonists should improve significantly the existing treatment for precocious puberty, endometriosis, uterine fibroids, polycystic ovary syndrome (PCO) and induction of ovulation although large scale trials comparing different therapies and doses are required. Finally, the concept of combination therapies to block further the influence of steroid hormones suggests challenging possibilities for even more effective therapy.

Chronic gonadotropin-releasing hormone agonist treatment suppresses ovulation and sexual behavior in group-living female rhesus monkeys

The sexual behavior of six adult rhesus females was observed with each of four males prior to, during, and following a 90 day treatment with 20 micrograms/day of a gonadotropin releasing-hormone (GnRH) agonist (WY-40972). All females ovulated, approached males and copulated during an untreated cycle. No ovulations occurred during agonist treatment and all females showed reduced sexual interest during the last 25 treatment days. Three females showed elevated estradiol and copulated during the first 10 days of agonist treatment, but never showed similar levels of estradiol or copulation during the rest of treatment. Within 34 days after agonist treatment, all females initiated proximity to males, copulated, and ovulated. All females became pregnant on their second ovulation after agonist treatment. This demonstration that inhibition of ovulation with a GnRH agonist decreased rhesus female sexual initiation, demonstrates the importance of ovarian hormones to female sexual motivation and suggests that the changes in human female sexual interest should be evaluated during the development of agonist-based contraceptives.

Ablation of folliculogenesis in women by a single dose of gonadotropin-releasing hormone agonist: significance of time in cycle

Effects of single subcutaneous doses (1, 5, 20, and 100 micrograms) of nafarelin, a potent gonadotropin-releasing hormone agonist, on the physiologic events of the human menstrual cycle were studied in 28 normal women. Nafarelin entered the circulation rapidly after injection. Peak concentrations were observed within 1 hour, and the plasma half-life was 4 to 5 hours. Maximal concentrations of luteinizing hormone and follicle-stimulating hormone were reached 3 to 4 hours after nafarelin administration. The magnitude of the gonadotropin responses depended both on the phase of the menstrual cycle (smallest responses during the early follicular phase) and the dose of nafarelin. Nafarelin administration during the early follicular phase delayed ovulation by 4.6 +/- 1.7 (standard deviation) days and prolonged the duration of the menstrual cycle from a pretreatment length of 29.2 +/- 2.1 days to 33.4 +/- 4.0 days (P less than 0.001). When nafarelin was administered shortly before or after ovulation, cycle length was not altered consistently. Administration 5 to 10 days after ovulation resulted in a truncated luteal phase. These observations suggest that the hormonal events triggered by nafarelin during the early follicular phase temporarily arrest the process of selection of the dominant follicle. Repeated intermittent administration of nafarelin or other gonadotropin-releasing hormone agonists in the early follicular phase may prevent follicular maturation and ovulation and may be a practical approach to contraceptive development.