Hormonal Suppression in Female Rhesus Macaques (Macaca mulatta) Implanted Subcutaneously with Deslorelin

Long-acting reversible contraception with etonogestrel implants in female macaques (Macaca mulatta and Macaca fascicularis)

Introduction

Contraception is often required for management and population control purposes in group-housed and free-roaming non-human primates. Long-acting reversible contraceptives, including subdermal progestin-releasing implants, are preferred as they eliminate challenges associated with frequent administration. Etonogestrel (ENG)-releasing subdermal implants are reversible and long-acting for a minimum of 3 years, and are commercially available for human use as Implanon® or Nexplanon®.

Methods

A retrospective analysis was performed detailing the contraceptive effectiveness and reversibility of subdermal placement of one-fourth or one-third of an ENG implant (68 mg/implant) in 129 female rhesus macaques (Macaca mulatta) and 67 cynomolgus macaques (Macaca fascicularis) at the Biomedical Primate Research Centre (Rijswijk, Netherlands). Furthermore, single cross-sectional ENG serum concentrations were measured for 16 rhesus and 10 cynomolgus macaques, and hemoglobin and blood chemistry pre-ENG and at timepoints >0.5, >1.5, and > 2.5 years post-ENG insertion were evaluated for 24 rhesus macaques. Finally, data were obtained using trans-abdominal ultrasound regarding the influence of ENG on uterine volume and endometrial thickness in 14 rhesus and 11 cynomolgus macaques.

Results

As a contraceptive ENG was in 99.80% (CI 93.50-99.99) and 99.95% (CI 99.95-100) effective in rhesus and cynomolgus macaques, respectively. Prolonged ENG durations of implant use in 14 rhesus macaques (range 3.1-5.0 years) and eight cynomolgus macaques (range 3.2-4.0 years) resulted in no unintended pregnancies. A total of 17 female macaques were allowed to breed after ENG removal, and among them, 14 female macaques (82%) had an uneventful delivery. Serum ENG concentrations with a median ENG duration of 1.2 years (range 0.1-6.0 years) and 1.9 years (range 0.6-4.7 years) resulted in median concentrations of 112 pg./mL (range 0-305 pg./mL) and 310 pg./mL (range 183-382 pg./mL) for rhesus and cynomolgus macaques, respectively. ENG had no clinical effect on hemoglobin and blood chemistry parameters nor on the thickness of the endometrial lining or uterus volume.

Conclusion

This study indicates that both one-fourth and one-third of the ENG implants are effective, long-acting, reversible, and safe contraceptive to use in macaques.

Physiological and behavioral effects of hormonal contraceptive treatment in captive, pair-bonded primates (Plecturocebus cupreus)

Hormonal contraception is an effective, reversible tool for managing birth rates in humans and nonhuman animals alike. However, manipulating reproductive hormones has behavioral consequences that can impact social and sexual behavior between conspecifics. First, we studied 18 pairs of nonreproductive titi monkeys (Plecturocebus cupreus) to test the efficacy of a novel method of hormonal contraception (deslorelin acetate implants) on reproductive hormone cycling in females and found significant reductions in urinary estrogens and progestagens among treated females compared to untreated controls. We then studied 35 nonreproductive pairs of coppery titi monkeys (Plecturocebus cupreus) to ascertain whether treating females with one of 2 different forms of hormonal contraception (deslorelin acetate implants (n = 17) or medroxyprogesterone acetate injections (n = 9)) would influence the relationship between pair mates compared to the relationship between untreated females and their vasectomized male mates (n = 9). Over a 5-month period, we found no differences in affiliative behaviors between pairs containing untreated females compared to pairs in which the female was treated with either deslorelin acetate or medroxyprogesterone acetate. Similarly, we found no differences in affiliation between pairs in the 2 treatment groups. This study is the first to examine behavioral consequences of hormonal contraception in a pair-bonding species. The results are encouraging for captive, managed breeding colonies of such social animals, especially those used in behavioral research.

Effects of Deslorelin on Testosterone Secretion and Testicular Volume in Male Rhesus Macaques (Macaca mulatta)

Sterility in male NHP has long been achieved through surgical castration or vasectomy. However, these techniques are irreversible, require a surgical procedure, and have potential consequences such as sperm granulomas and long recovery time. Deslorelin is a gonadotropin-releasing hormone agonist that temporarily and reversibly suppresses sex hormone secretion. Our goal in this study was to investigate the effects of deslorelin on testosterone secretion and testicular volume in male rhesus macaques (Macaca mulatta). Male macaques (n = 4) each received two, 4.7-mg deslorelin implants subcutaneously in the interscapular region. Serum testosterone and testicular volume were then monitored at specific time points until 10 mo after treatment. Testosterone suppression was defined as testosterone levels lower than 0.6 ng/mL for a sustained period of at least 30 d. After implantation, mean testicular volume was significantly reduced by day 121. Testosterone suppression was observed in all subjects. However, the time from implantation to testosterone suppression and duration of suppression varied. Two macaques were hormonally suppressed by day 26 after implantation and remained suppressed for at least 6 mo. The other 2 macaques were hormonally suppressed by 2 mo after implantation; of these two, one remained suppressed for 70 days while the other was suppressed for at least 245 days. We conclude that deslorelin can safely suppress testosterone secretion in male rhesus macaques, but individual variation in onset and duration of action should be considered when establishing reimplantation time points and potential return to reproductive activity.