Inhibition of ovulation by intranasal nafarelin, a new superactive agonist of GnRH

GnRH analogues—agonists and antagonists

GnRH analogues have achieved widespread clinical use for the control of reproduction in animals. Over 2000 analogues of GnRH have been developed and tested over the last 30 years. Paradoxical anti-fertility effects are seen when the more potent agonists are delivered continuously to animals. The evaluation of agonist potency depends largely on the model used and wide varying potencies are reported for the same agonist. The design of analogues has centered on improving the receptor-binding and subsequent activation for agonists. Antagonists have been produced with strong receptor binding but without activation. Deslorelin is classified as a superagonist, with a potency perhaps 100 times that of GnRH. The interactions between agonist potency, dose and duration of treatment largely determine whether pro- or anti-fertility effects are induced. Due to the peptide nature of the synthetic analogues oral administration and potential gastrointestinal enzymatic degradation poor bioavailability results necessitating a parenteral delivery system. Some GnRH antagonists have been associated with significant histamine release, inhibiting their widespread use. More recently, antagonists have been developed that avoid this side effect without compromising potency. However the GnRH antagonist development has lagged behind that of the agonists, in part related to their high cost of production. In conclusion, GnRH agonists have achieved widespread clinical use in animals for controlling reproduction in either pro- or anti-fertility roles, yet antagonist development has been slower.

LH-RH analogues: I. Their impact on reproductive medicine

In the 28 years that have passed since the elucidation of the structure of luteinizing hormone-releasing hormone (LH-RH), diverse clinical applications in the field of reproductive medicine and related fields have been established for agonists of LH-RH, based on inhibition of the pituitary-gonadal axis. Various clinical investigations with agonists of LH-RH in benign gynecologic disorders, polycystic ovary disease (PCOD), in vitro fertilization-embryo transfer (IVF-ET), benign prostatic hypertrophy (BPH), precocious puberty and contraception were reviewed. LH-RH antagonists inhibit LH, follicle-stimulating hormone (FSH), and sex steroid secretion immediately after their administration and thus achieve rapid therapeutic effects. LH-RH antagonists should find applications in the treatment of uterine leiomyomas, endometriosis, and in controlled ovarian stimulation-assisted reproductive techniques (COS-ART), which have been already established for the agonists. Modern LH-RH antagonists such as cetrorelix may prove superior to the agonists in COS-ART and also in the treatment of BPH, but additional studies in these and other areas are needed.

Luteinizing hormone-releasing hormone analogs: their impact on the control of tumorigenesis

The development of the luteinizing hormone-releasing hormone (LH-RH) agonists and antagonists and the principles of their clinical use were reviewed. In the 28 years that have elapsed since the elucidation of the structure of LH-RH, various applications in gynecology, reproductive medicine, and oncology have been established for LH-RH agonists and antagonists. These clinical applications are based on inhibition of the pituitary and the gonads. The advantage of the LH-RH antagonists is due to the fact that they inhibit the secretion of gonadotropins and sex steroids immediately after the first injection and thus achieve rapid therapeutic effects in contrast to the agonists, which require repeated administration. LH-RH antagonists should find applications in the treatment of benign gynecologic disorders and benign prostatic hypertrophy and in assisted reproduction programs. The primary treatment of advanced androgen-dependent prostate cancer is presently based on the use of depot preparations of LH-RH agonists, but antagonists like Cetrorelix already have been tried successfully. Antagonists of LH-RH might be more efficacious than agonists in treatment of patients with breast cancer as well as ovarian and endometrial cancer. Recently, practical cytotoxic analogs of LH-RH that can be targeted to LH-RH receptors on tumors have been synthesized and successfully tested in experimental cancer models. Targeted cytotoxic LH-RH analogs show a great promise for therapy of prostate, breast, and ovarian cancers.

Two-step gonadotropin-releasing hormone agonist treatment of uterine leiomyomas: standard-dose therapy followed by reduced-dose therapy

OBJECTIVE

Gonadotropin-releasing hormone agonist-induced partial pituitary suppression with low-grade estrogen production may be useful in long-term treatment of uterine leiomyomas.

STUDY DESIGN

Twenty-seven women with uterine leiomyomas were treated with a standard dose of triptorelin for 8 weeks. Patients were then randomized to use 100, 20, or 5 micrograms of triptorelin until week 26. Uterine and myoma size, pituitary-ovarian function, bone metabolism, and bone mineral density were monitored.

RESULTS

During standard treatment uterine size was reduced to 67.1% of baseline. During randomized treatment uterine size was further reduced to 57.8% of baseline. There were no differences in overall volume reduction among the groups. Luteinizing hormone and estradiol levels were restored in a dose-dependent way. Bone mineral density decreased significantly in the highest-dose group at week 26.

CONCLUSIONS

This study shows that the beneficial effects of initial high-dose agonist treatment on uterine leiomyomas can be preserved by continued low-dose treatment. Bone mineral density does not seem to change during reduced-dose agonist treatment.

Cyclical breast pain and swelling in relation to differing patterns of suppression of ovarian activity with the luteinizing hormone-releasing hormone analogue buserelin acetate: case report

The presenting complaints of an amenorrhoeic (after hysterectomy with ovarian preservation) woman were cyclical breast pain and swelling. These showed synchronicity with fluctuations in E2 levels. Both ovarian activity and symptoms initially responded to (after lag periods of approximately 40 days) daily SC injections of the LH-RH analogue buserelin acetate. After a break in treatment, the interval between reinitiation of therapy and suppression of E2 levels was prolonged markedly, ovarian function being apparently resistant even to very large doses of the analogue.

Ovarian sonographic findings during intermittent intranasal luteinizing hormone-releasing hormone agonist sequentially combined with an oral progestogen as antiovulatory contraceptive approach

Ovarian ultrasounds were performed in four groups of six or seven women taking intranasal luteinizing hormone-releasing hormone agonist Buserelin (200 micrograms twice daily or 400 micrograms once daily) for periods of 14 or 21 days. Medroxyprogesterone acetate (5 mg by mouth twice daily) was added on days 15 to 21. A pause of 7 days followed each of the four treatment periods. Between days 12 to 15 of the first Buserelin cycle, sonograms showed in 17 cases (68%) various degrees of follicular stimulation ranging from numerous 4- to 10-mm follicles (24%), to 10- to 27-mm developing follicle(s) (24%), to greater than 27-mm ovarian cysts (20%). At the fourth Buserelin cycle, the predominant observation was large follicle(s) in the 14-day schedules, whereas ovarian scans did not reveal follicular stimulation in 66% of the 21-day schedules. The area under estradiol (E2) curves was above control in cycles with induced large follicles mainly in the 14-day schedules at the 200 micrograms/12 hour dose. Occasional brief and low elevation of progesterone was compatible with luteinized follicles. In the 21-day schedules at 400 micrograms/24 hours, absence of follicular development was frequently associated with serum E2 in the early follicular phase range. The most appropriate dosage regimen for potential contraception was 200 micrograms/12 hours for 21 days because it was associated with small follicles and serum E2 was in the range of control cycles.

Intranasal peptide contraception by inhibition of ovulation with the gonadotropin-releasing hormone superagonist nafarelin: six months' clinical results

Forty-seven woman volunteers used a new highly potent stimulatory analog of the hypothalamic gonadotropin-releasing hormone (GnRH) for contraception. The superagonist nafarelin acetate, D-Nal(2)6-GnRH, was administered intranasally in one daily dose of 125 micrograms to 25 women and 250 micrograms to 22 women. Ovulation was consistently inhibited during 261 of 262 treatment months. No pregnancy occurred during 222 months in which no additional contraceptives were used. The mean plasma estradiol level after 6 months of treatment was 162 pmol/l. The predominant bleeding pattern was oligomenorrhea. Three women on the lower dose and six women on the higher dose discontinued the trial prematurely, mainly because of hot flushes. No serious side effects were reported. Ovulatory menstruations returned after a median time of 43 days after discontinuation of therapy. Daily intranasal nafarelin treatment for inhibition of ovulation proved to be an effective and rapidly reversible method of contraception.

Recent developments in female contraception: LHRH

During the last few years new approaches to female contraception based on LHRH and its analogs have been developed. The physiological significance of pulsatile LHRH release and its stimulation of the pituitary has been elucidated by recent studies in rhesus monkey. Immunization against LHRH results in complete inhibition of reproductive function in animals and may find as a useful method of long-term fertility control in domestic animals. Clinical studies have utilized this knowledge to treat infertile hypogonadal women with chronic intermittent low-dose of LHRH. The superactive stimulatory LHRH analogs, used to treat infertility, paradoxically proved to have antifertility effects. They induce desensitization of the processes responsible for gonadotropic and gonadal hormone secretion, mediated by specific LHRH receptors in the pituitary and gonad. While contraceptive effectiveness of luteolytic approach remains to be proven, inhibition of ovulation by intranasal LHRH analog administration or continuous LHRH infusion by programmed minipumps seem to provide safe and effective contraception in women.