A combined oral contraceptive affects mucosal SHIV susceptibility factors in a pigtail macaque model

Background—Injectable hormonal contraception may increase women’s risk of HIV acquisition, and can affect biological risk factors in animal models of HIV. We established, for the first time, a model to investigate whether combined oral contraceptives (COC) alter SHIV susceptibility in macaques. Methods—Seven pigtail macaques were administered a monophasic levonorgestrel (LNG)/ ethinyl estradiol (EE) COC at 33% or 66% of the human dose for 60 days. Menstrual cycling, vaginal epithelial thickness and other SHIV susceptibility factors were monitored for a mean of 18 weeks. Results—Mean vaginal epithelial thicknesses was 290.8 μm at baseline and 186.2 μm during COC (p=0.0141, Mann Whitney test). Vaginal pH decreased from 8.5 during to 6.5 posttreatment (0.0176 two-tailed t-test). Measured microflora was unchanged. Conclusions—COC caused thinning of the vaginal epithelium and vaginal pH changes, which may increase SHIV susceptibility. 0.033 mg LNG + 0.0066 mg EE appeared effective in suppressing ovulation.