A non-human primate study (baboon; Papio hamadryas) to determine if a long-acting progestogen, levonorgestrel butanoate, combined with a long-acting androgen, testosterone buciclate, can suppress spermatogenesis: I. Dose-finding study

Effects of levonorgestrel butanoate alone and in combination with testosterone buciclate on spermatogenesis in the bonnet monkey

The spermatogenic effects of levonorgestrel butanoate were studied in adult male bonnet monkeys when administered alone and in combination with testosterone buciclate. Levonorgestrel butanoate (0.25, 1.0 and 2.5 mg kg(-1)) given as two injections on days 0 and 60 (groups II, III, IV) resulted in thickening and folding of the basement membrane and disruption of cell associations in groups III and IV (on day 120). In group II, no apparent changes in testicular histology were observed. When these doses of levonorgestrel butanoate were combined with 40 mg of testosterone buciclate (groups V, VI, VII), maximum changes were seen in group VI in which all stages of spermatogenesis were absent on day 120 except for a small number of spermatogonia. The changes caused by lower dose (group V) and higher dose (group VII) of levonorgestrel butanoate were less prominent than in group VI. A significant decrease in the number of dark A (Ad) and B spermatogonia was observed in all groups except for Ad spermatogonia on day 120 in group V, B spermatogonia on day 60 in group IV and B spermatogonia on day 120 in group III. A significant decrease in pachytene spermatocytes was seen on day 120 in groups V only. Early spermatids showed a significant decrease only in groups V and VII on day 120 of treatment. Advanced spermatids were suppressed significantly in group IV on day 60 and in groups IV and V on day 120. These data indicate that levonorgestrel butanoate (1.0 mg kg(-1)) in combination with 40 mg of testosterone buciclate was the most effective treatment in suppressing spermatogenesis. The site of action of this combination regimen is at the level of renewing Ad spermatogonia.

Pharmacological developments in male contraception

To date, the current methods of male contraception are limited to condoms, coitus interruptus and vasectomy, all of which are beset with difficulties. The condom is inconvenient, dulls sensation, and although somewhat effective against sexually transmitted disease, has an increased failure rate over time of usage. Coitus interruptus reduces the pleasurable aspects of intercourse and is plagued with a high failure rate. Vasectomy is virtually sterilisation. The current research into new forms of contraception is as diverse as the mechanisms controlling male fertility. The majority of effort has focused on antispermatogenic agents. Hormonal agents that suppress spermatogenesis appear nearest to final development and are primarily centred around various testosterone esters. These can be administered alone or in combination with progestogens. Another promising line of study centres on gonadotropin releasing hormone (GnRH) antagonism resulting in suppression of gonadotropins. Non-hormonal antispermatogenic agents include numerous phytochemicals, and testicular enzyme inhibitors. Post-testicular approaches to male contraception include agents that interfere with sperm metabolism, motility, maturation or transport. This review summarises recent clinical and animal studies on these compounds with emphasis on their mechanism of action, advantages and drawbacks.

Baboon spermatozoa-zona pellucida binding assay

This study developed a baboon in vitro system that allows transport of sperm from a treatment facility to an off-site location for subsequent evaluation of sperm functional capacity. We further described a sperm functional assay that evaluates baboon sperm binding to homologous zona pellucida, a baboon hemizona assay (HZA). Semen samples were collected from baboons via electroejaculation directly into refrigeration transport buffer. Postshipment semen characteristics were analyzed and each specimen prepared for assessment of sperm-zona pellucida interaction. Optimization of the baboon HZA included determination of the relationship between motile sperm concentration and zona pellucida binding. The effect of the sperm activators, caffeine and dbcAMP, on computerized sperm motion characteristics and HZ binding was also determined. A significant motile sperm concentration dependent increase was observed in sperm-zona pellucida binding. Maximal binding was observed at approximately 1-2 million motile sperm/mL. Treatment with the sperm activators, caffeine and dbcAMP, resulted in a significant increase in sperm progressive motility, straightline velocity (VSL), and amplitude of lateral head displacement (ALH), p <0.05 and a highly significant increase in curvilinear velocity (VCL), p <0.01. Treatment with caffeine and dbcAMP was not an absolute requirement for sperm-zona pellucida binding, inasmuch as binding did occur in the absence of activators. However, treatment with the two activators, caffeine and dbcAMP, resulted in a highly significant increase in HZ binding, p <0.0001. This system allows for the short-term maintenance of baboon sperm in a semiquiescent state until stimulation with the activators, caffeine and dbcAMP. It further provides a novel approach to delineating a contraceptive regimen's or agent's (ie, sperm vaccine) impact on specific cellular events occurring in the male gamete during fertilization.

Rates of testosterone-induced suppression to severe oligozoospermia or azoospermia in two multinational clinical studies. World Health Organization Task force on Methods for The Regulations of Male Fertility

Two multicentre studies of the contraceptive efficacy of azoospermia and severe oligozoospermia were conducted in 16 centres in 10 countries. They used a common protocol of weekly testosterone injections for sperm suppression, the patterns and degrees of which were compared among men from different population groups. Six hundred and seventy normal, health volunteers, of whom 205 were Asian (mostly Chinese) and 465 of non-Asian origin, were given weekly injections of testosterone enanthate, 200 mg IM, during the suppression (6-month) and efficacy (12-month) phases. Patterns of sperm suppression were assessed by semen analysis at monthly or 2-weekly intervals. Sperm counts suppressed more slowly in the Asian than in the non-Asian men in the first 2 months of injections but subsequently suppressed to lower sperm concentrations below 5 million/ml, 3 million/ml or azoospermia at 6 months were 97.1% 95.6%, and 66.7%, respectively for non-Asian men, compared to 99.4%, 98.4% and 89.2%, respectively for Asian men. In conclusion, a hormonal contraceptive method based on regular testosterone injections can suppress spermatogenesis to azoospermia or severe oligozoospermia in 97% of men, regardless of their ethnic origin.

A non-human primate study (baboon; Papio hamadryas) to determine if a long-acting progestogen, levonorgestrel butanoate, combined with a long-acting androgen, testosterone buciclate, can suppress spermatogenesis: II. Efficacy study

Two combined injections of levonorgestrel butanoate (4 mg/kg) and testosterone buciclate (8 mg/kg) at 3-month intervals to adult male baboons initiated a decrease in sperm concentration from baseline values of 490x10(6)/ml to minimum values of 17x10(6/ml. This suppression was sustained until week 32, during which time between one and three azoospermic samples were collected from each of four out of five treated baboons in the period 10-24 weeks. Circulating plasma levels of LH and testosterone decreased to approximately 20-75% of baseline values. Plasma levels of cortisol declined to significantly reduced levels at weeks 22 and 36-44. All values returned to the baseline range by week 48. The combined administration of progestogen and androgen induced a more marked and sustained suppression to severe oligozoospermia or azoospermia than did the equivalent dose of progestogen alone (Goncharov et al., 1995). Although the dose of testosterone buciclate used did not maintain peripheral levels of testosterone in the normal range, it did not restimulate spermatogenesis. It was concluded that a combination drug regimen based on the novel long-acting levonorgestrel and testosterone esters could provide a contraceptive option for men.