Norethisterone enanthate has neither a direct effect on the testis nor on the epididymis: a study in adult male cynomolgus monkeys (Macaca fascicularis)

Insights into the fatty acid ester norethisterone enanthate binding to human albumin: fluorescence, circular dichroism, and docking investigations

Fatty acid ester norethisterone enanthate binding to human albumin.

Experimental endocrine manipulation by contraceptive regimen in the male marmoset (Callithrix jacchus)

Marmosets are used as preclinical model in reproductive research. In contrast to other primates, they display short gestation times rendering this species valid for exploration of effects on fertility. However, their peculiar endocrine regulation differs from a those of macaques and humans. We subjected male marmosets to previously clinically tested hormonal regimens that are known to effectively suppress spermatogenesis. Beside a control group, seven groups (each n=6) were investigated for different periods of up to 42 months: regimen I, (four groups) received testosterone undecanoate (TU) and norethisterone enanthate (NETE); regimen II, (two groups) received TU and NETE followed by NETE only; and regimen III, (one group) received NETE only. Testicular volume, cell ploidy and histology, endocrine changes and fertility were monitored weekly. TU and NETE and initial TU and NETE treatment followed by NETE failed to suppress spermatogenesis and fertility. Testicular volumes dropped, although spermatogenesis was only mildly affected; however, testicular cellular composition remained stable. Serum testosterone dropped when NETE was given alone but the animals remained fertile. Compared with controls, no significant changes were observed in sperm motility and fertility. Administration of TU and NETE affected testicular function only mildly, indicating that the regulatory role of chorionic gonadotrophin and testosterone on spermatogenesis is obviously limited and testicular function is maintained, although the endocrine axis is affected by the treatment. In conclusion, marmosets showed a different response to regimens of male contraception from macaques or men and have to be considered as a problematic model for preclinical trials of male hormonal contraception.

Advances in male contraception

Despite significant advances in contraceptive options for women over the last 50 yr, world population continues to grow rapidly. Scientists and activists alike point to the devastating environmental impacts that population pressures have caused, including global warming from the developed world and hunger and disease in less developed areas. Moreover, almost half of all pregnancies are still unwanted or unplanned. Clearly, there is a need for expanded, reversible, contraceptive options. Multicultural surveys demonstrate the willingness of men to participate in contraception and their female partners to trust them to do so. Notwithstanding their paucity of options, male methods including vasectomy and condoms account for almost one third of contraceptive use in the United States and other countries. Recent international clinical research efforts have demonstrated high efficacy rates (90-95%) for hormonally based male contraceptives. Current barriers to expanded use include limited delivery methods and perceived regulatory obstacles, which stymie introduction to the marketplace. However, advances in oral and injectable androgen delivery are cause for optimism that these hurdles may be overcome. Nonhormonal methods, such as compounds that target sperm motility, are attractive in their theoretical promise of specificity for the reproductive tract. Gene and protein array technologies continue to identify potential targets for this approach. Such nonhormonal agents will likely reach clinical trials in the near future. Great strides have been made in understanding male reproductive physiology; the combined efforts of scientists, clinicians, industry and governmental funding agencies could make an effective, reversible, male contraceptive an option for family planning over the next decade.

GnRH-antagonist mediated down-regulation of the estrous cycle in marmosets

BACKGROUND

Because of its small size and unproblematic captivity behavior the marmoset monkey is an attractive New World primate model for early developmental questions. However, superovulation protocols used in Old World monkeys and women are not successful in the female marmoset. A novel protocol is needed to utilize these New World monkeys as an efficient animal model for in vitro fertilization experiments or embryo stem cell research.

METHODS

To create such a protocol we first examined the effects of long-term estrous cycle control, secondly, in a dose-finding study, we determined the length of a down-regulation protocol with a gonadotropic releasing hormone (GnRH)-antagonist. Twenty-nine female marmosets were grouped according to the number of estrous cycles, which had been controlled for a period of 12 months in which 88 cycles were monitored. Application of PGF2alpha in the mid-luteal phase led to immediate onset of the follicular phase. The blood progesterone concentration rapidly declined and increased again on day 9-11.

RESULTS

The results show that the controlled ovarian cycle length and progesterone response are not altered by the number of PGF2alpha injections. The rapid decline was similar in all groups, indicating that all animals, independent of the number of controlled cycles, react equally to multiple PGF2alpha injections. To determine the proper dosage for a GnRH-antagonist (Cetrorelix), 12 animals in three groups of four female marmosets were treated with two different dosages and a sham dosage. Cetrorelix was applied in the mid-luteal phase, three times over 2 days. In both Cetrorelix-treated animal groups the early progesterone levels matched those in the controls. In the low-dose treatment group [0.01 mg/100 g body weight (BW)] the expected progesterone rise on day 10 was delayed between 9 and 15 days whereas in the high-dose treatment group (0.1 mg/100 g BW) the progesterone rise was delayed between 21 and 41 days. In the low-dose group the steepness of the slope from day 20 onwards was almost identical to that of the control group. This was reflected in the bioCG levels measured.

CONCLUSIONS

Based on the GnRH-antagonist studies, complete ovarian down-regulation in female marmosets can be achieved by applying a low-dose regimen, and intrinsic gonadotropins would not interfere with an ovarian superstimulation protocol.

Drug Insight: recent advances in male hormonal contraception

As there are limitations to current methods of male contraception, research has been undertaken to develop hormonal contraceptives for men, analogous to the methods for women based on estrogen and progestogens. When testosterone is administered to a man, it functions as a contraceptive by suppressing the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary gland. Since these hormones are the main stimulatory signals for spermatogenesis, low levels of LH and FSH markedly impair sperm production. After 3-4 months of testosterone treatment, 60-70% of men no longer have sperm in their ejaculate, and most other men exhibit markedly diminished sperm counts. Male hormonal contraception is well tolerated, free of serious adverse side effects, and 95% effective in the prevention of pregnancy. Importantly, male hormonal contraception is reversible, with sperm counts usually recovering within 4 months of the discontinuation of hormone treatment. Because exogenous testosterone administration alone does not completely suppress sperm production in all men, researchers have combined testosterone with second agents, such as progestogens or gonadotropin-releasing-hormone antagonists, to further suppress secretion of LH and FSH and improve suppression of spermatogenesis. Recent trials have used combinations of long-acting injectable or implantable forms of testosterone with progestogens, which can be administered orally, by injection or by a long-acting implant. Such combinations suppress spermatogenesis to zero without severe side effects in 80-90% of men, with near-complete suppression in the remainder of individuals. One of these testosterone and progestogen combination regimens might soon bring the promise of male hormonal contraception to fruition.