OR27-03 Duration of Testosterone-Induced Acyclicity Influences Corpora Lutea Formation and Stromal Changes in a Transgender Mouse Model

The impact and reversibility of long-term gender-affirming testosterone (T) therapy on the reproductive axis of transgender men has not been well-established. Little is known about outcomes for transgender men interested in pausing T therapy to harvest oocytes or get pregnant. We previously established a translational mouse model to investigate T-induced acyclicity and ovarian perturbations. We hypothesized that the duration of T-induced acyclicity would impact the reversibility of cyclic and ovarian changes. To test this hypothesis, T-treated mice were assigned to two groups: (SHORT) 6 weeks of T therapy with immediate reversibility (1.5 mg T propionate pellet implant/removal, n = 5) and (LONG) 6 weeks of T therapy with a prolonged T washout phase (subcutaneous oil injections of T enanthate at 0.9 mg once weekly, n = 5). Control groups (placebo pellets n = 5, sesame oil vehicle injections n = 5) were run in parallel. Estrous cycles were monitored using daily vaginal cytology. Following cessation of T therapy, mice were sacrificed in diestrus after resumption of cyclicity for 4 cycles and ovarian histology examined. Data were analyzed in GraphPad Prism using Welch’s t-test or Mann-Whitney where appropriate. T therapy led to persistent diestrus within a week after T administration for all T-treated mice and none of the controls. The total duration of acyclicity was 6±1 weeks for the SHORT group, which was significantly shorter than the 11±2 weeks for the LONG group (mean ± s.d., p = 0.0079). With resumption of cyclicity, both the SHORT and LONG groups had a significantly lower percentage of days in estrus and higher percentage of days in metestrus as compared to their parallel age-matched controls. Ovarian histology for the SHORT group all showed regular corpora lutea and minimal stromal changes, however, 3/5 mice in the LONG group lacked corpora lutea and 4/5 revealed marked stromal cell hypertrophy. Similar stromal cell changes were not seen in control mice. In conclusion, the length of time of T-induced acyclicity appears to impact the development of stromal cell hypertrophy and formation of corpora lutea even after resumption of cyclicity with similar alterations to the estrous cycles. These findings may have clinical relevance for transgender men interested in fertility, based on duration of gender-affirming T therapy. Future work will aim to separate out the respective contributions of T exposure and acyclicity to the stromal phenotype.