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

Providing effective contraception for nonhuman primates (NHP) is challenging. Deslorelin acetate is a commercially available gonadotropin-releasing hormone (GnRH) agonist that may provide a relatively noninvasive, long-lasting, and potentially reversible alternative to standard NHP contraception methods. This study evaluated the duration of suppression of progesterone and estradiol in 6 adult female rhesus macaques (Macaca mulatta) that received a single subcutaneous 4.7 mg deslorelin implant. We hypothesized that deslorelin would suppress production of these hormones for 6 mo with a correspond- ing cessation of menses. Prior to implantation, blood was collected over 1 mo for baseline hormone analyses. Macaques were sedated at the onset of the next menstrual cycle and a 4.7 mg deslorelin implant was placed in the interscapular region. Blood was collected over the subsequent month at the same intervals used for the baseline collection schedule, and then every 7 d thereafter. Results showed that estradiol and progesterone transiently increased 1 to 3 d after implantation, then fell to basal levels within 6 d of implantation. The duration of hormone suppression (progesterone <0.5 ng/mL) varied among animals. Two macaques returned to cyclicity by 96 d and 113 d after implantation, while hormones remained suppressed in the other 4 macaques at 6 mo after implantation. Cessation of menses correlated with hormone suppression except in 1 animal that continued to have sporadic vaginal bleeding despite progesterone remaining below 0.5 ng/mL. This study indicates that deslorelin is a noninvasive and long-lasting contraceptive method in female rhesus macaques. However, individual variation should be considered when determining reimplantation intervals.