“Androgenic capacity of the follicle-depleted ovary in VCD-treated mice”

ABSTRACT
One unresolved question related to residual ovarian tissue in post-menopausal women is whether it retains steroidogenic capacity and produces androgens. Moreover, contributions of this tissue to the physiology of post-menopausal women have not been determined. An ovary-intact mouse model of natural menopause has been developed using the chemical 4-vinylcyclohexene diepoxide (VCD). Daily dosing of mice and rats with VCD selectively destroys ovarian primordial and primary follicles by accelerating the normal process of atresia. When given at a high dose, VCD causes early ovarian failure in mice. Because remaining larger follicles are not directly affected, the animal ovulates normally, progresses gradually into ovarian failure and retains residual ovarian tissue. Thus, the VCD-treated mouse is a relevant model for studying the follicle-depleted ovary and its potential impact on post-menopausal women’s health. The purpose of this study was to characterize the capacity of residual ovarian tissue in the VCD-treated follicle-depleted mouse. Female B6C3F1 mice (28-days old) were dosed daily with either VCD or sesame oil (vehicle control) for 20 days. Vaginal cytology was performed daily to monitor estrous cyclicity of each animal and assign ovarian failure in the treatment group. Ovaries were collected on d120 or d181 after the onset of dosing. Expression of mRNA encoding low density lipoprotein receptor (LDLR), cholesterol side chain cleavage enzyme (Cyp11a) and 17α-hydroxylase (Cyp17) was determined by real-time PCR. Expression of oocyte-specific genes Zygote arrest 1 (Zar1) and Zona pelucida glycoprotein 3 (Zp3) was used as a negative control for follicle-depleted ovaries. Relative to cycling controls, residual ovarian tissue in VCD-treated animals was highly enriched (ratio VCD-treated/cycling controls, P<0.05) in mRNA encoding LDLR (d120, 1.83 ± 0.03; d181 5.31 ± 0.11), Cyp11a (d120, 1.55 ± 0.29; d181, 2.48 ± 0.25) and Cyp17 (d120, 114.63 ± 0.30; d181, 147.71 ± 0.14). Conversely, mRNAs encoding the oocyte-specific genes Zar1 and Zp3 were undetectable in all follicle-depleted ovaries. Circulating levels of androstenedione were measured at selected time points during the period following the onset of dosing. On most of the time points measured there was no difference (P>0.05) in circulating androstenedione between groups (range 0.15-1.16ng/ml). At the d120 time point circulating androstenedione levels were lower (P<0.05) in VCD-treated animals (0.30 ± 0.13 ng/ml); whereas, on d181 there was no difference (control, 0.15 ± 0.048; VCD, 0.32 ± 0.10 ng/ml). These data support that residual ovarian tissue in the follicle-depleted mouse retains the capacity to synthesize and secrete androgenic steroids. Further, this study demonstrates that the VCD-treated mouse model of menopause may be relevant for understanding physiological contributions of the ovary in post­menopausal women. (AG021948)