Synthetic estrogen and progestin effects on the myogenic program following damage in C2C12 murine myoblasts.

Females exhibit distinct responses to exercise-induced muscle damage, possibly due to circulating hormone profiles. Despite the widespread use of oral contraceptives (OC) among females, the muscle damage and repair response during synthetic hormone use remains unknown. This study investigated how ethinyl estradiol (EE) and synthetic progestins [representing the different OC generations: medroxyprogesterone acetate (MPA), OC1; levonorgestrel (LNG), OC2; desogestrel (DSG), OC3; and drospirenone (DRP), OC4] influence C2C12 myoblast behavior. We examined proliferation, differentiation, and migration at baseline and following electrical pulse stimulation (EPS). While MPA and LNG alone increased myoblast proliferation (~19%; p < 0.05), their combination with EE (creating OC1 and OC2, respectively) reduced proliferation (15%-17%; p < 0.05) versus the vehicle control (VEH). All OC formulations significantly impaired migration (46%-61%; p < 0.001) without affecting differentiation. Post-EPS, only OC1 and OC2 conditions showed elevated creatine kinase alongside upregulated early myogenic proteins and modulation of hormone receptors. These results indicate that synthetic sex hormones in OCs can significantly alter myoblast responses to damaging stimuli in a generation-specific manner. OC use may influence muscle repair processes differently than natural hormonal profiles, highlighting the need for further investigation into how contraceptive formulations affect exercise recovery in women.