Estrogen receptor (ER)-α, β and progesterone receptor (PR) mediates changes in relaxin receptor (RXFP1 and RXFP2) expression and passive range of motion of rats' knee

- We investigated changes in the knee range of motion in the presence of Estrogen/Progesterone.
- We found a relationship between knee laxity and sex-steroids.
- We investigated the interaction of Estrogen/Progesterone antagonists to relaxin receptors.
- Estrogen/Progesterone are involved in the structures controlling knee joint movements.

PurposeThe high risk of knee injuries in female may be associated with sex-steroid hormone fluctuations during the menstrual cycle by its effect on ligaments and tendons stiffness. This study examined changes in knee range of motion in presence of estrogen and progesterone and investigated the interaction of their antagonists to relaxin receptors.MethodSixty WKY rats were divided into 10 different groups receiving 17β-estradiol (0.2, 2, 20 and 50 μg/kg), progesterone (4 mg/kg), estrogen receptor (ER) antagonist ICI 182/780, ERβ antagonist PHTPP, ERα antagonist MPP, and mifepristone in presence of estrogen and progesterone. Physiologic dose were injected subcutaneously 30 min before of hormone injection for 3 days consequently. Sham group received peanut oil (vehicle) also for 3 consecutive days. Following the treatment administrations, the knee range of motion and RXFP1/RXFP2 mRNA and protein expression were examined in the patellar tendon, lateral collateral ligament, and hamstring muscle.ResultsOur data showed that the knee range of motion was significantly increased in progesterone and high doses estrogen treatment but not significantly increased in low doses of estrogen treatment. The range of motion was decreased in the presence of estrogen receptor (ER) antagonist ICI 182/780, ERβ antagonist PHTPP, ERα antagonist MPP, and mifepristone, independently.ConclusionProgesterone and high doses of estrogen treatment resulted in the highest range of knee laxity correlated to expression of both relaxin receptor isoforms in knee tissues. Our findings thus suggested that female subjects are more vulnerable toward non-traumatic knee injury due to estrogen and progesterone fluctuation as compared to male subjects.