Continuous testosterone exposure alters body weight, lean mass, estrous cycling and lipid profile, but not wheel running in adolescent or adult female rats.

Health-related organizations have called for broadening biomedical research to include gender-diverse individuals. The present study tested the validity of an animal model of gender affirming testosterone therapy that may be useful for determining the impact of hormonal transition on a variety of health outcomes in both adolescents and adults. Blank or testosterone-filled capsules were implanted s.c. into gonadally intact adolescent (post-natal day 43) and adult (post-natal day 92) female rats. Body weight, estrous cycling, and home cage wheel running were recorded for 3 weeks; other physiological indices of defeminization and masculinization were assessed 29-30 days after capsule implantation. Testosterone treatment at male-typical levels suppressed estrous cycling and uterine weight, increased body weight and lean mass, and increased low density lipoprotein levels in both adolescents and adults. Testosterone increased clitoral gland size in adolescents. In contrast, wheel running was not significantly altered by testosterone. Results suggest that testosterone exposure at male-typical levels in gonadally intact female rats - whether adolescent or adult at the initiation of treatment - is a valid model of gender affirming testosterone therapy in terms of hormone impact on a variety of physiological measures. This model can thus provide a clinically relevant avenue for advancing transgender medicine.