Environmental Toxicology and Pharmacology 40 (2015) 785–791 Contents lists available at ScienceDirect Environmental Toxicology and Pharmacology j o ur na l ho mepage: www.elsevier.com/locate/etap Estrogen receptor (ER)-,  and progesterone receptor (PR) mediates changes in relaxin receptor (RXFP1 and RXFP2) expression and passive range of motion of rats’ knee Firouzeh Dehghan a,b,∗,1 , Ashril Yusof b , Sekaran Muniandy c , Naguib Salleh a,∗∗,1 a Department of Physiology, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia b Department of Exercise Science, Sports Centre, University of Malaya, Kuala Lumpur, Malaysia c Department of Molecular Medicine, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia a r t i c l e i n f o Article history: Received 27 May 2015 Received in revised form 4 September 2015 Accepted 5 September 2015 Available online 8 September 2015 Keywords: Knee laxity Relaxin receptor Estrogen Progesterone a b s t r a c t Purpose: The 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. Method: Sixty WKY rats were divided into 10 different groups receiving 17-estradiol (0.2, 2, 20 and 50 g/kg), progesterone (4 mg/kg), estrogen receptor (ER) antagonist ICI 182/780, ER antagonist PHTPP, ER 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. Results: Our 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, ER antagonist PHTPP, ER antagonist MPP, and mifepristone, independently. Conclusion: Progesterone 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. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Sex-steroids have been reported to regulate changes in knee laxity (Dehghan et al., 2014a,b). E 2 (estrogen) cause increased (Dragoo et al., 2009) while testosterone cause decreased (Dehghan et al., 2014a,b) knee laxity in rodents. In humans, knee laxity ∗ Corresponding author at: Department of Exercise Science, Sports Centre, Uni- versity of Malaya, 50603 Kuala Lumpur, Malaysia. Tel.: +601 0433 0893; fax: +603 7956 9590. ∗∗ Corresponding author at: Department of Physiology, Faculty of Medicine, Uni- versity of Malaya, 50603 Kuala Lumpur, Malaysia. Tel.: +603 7967 7532; fax: +603 7967 4775. E-mail addresses: fir dhn@yahoo.com (F. Dehghan), naguib.salleh@yahoo.com (N. Salleh). 1 Firouzeh Dehghan and Naguib Salleh have equal contribution in preparation of this manuscript. was reported to increase at around the time of ovulation, indi- cating of E 2 influence (Zazulak et al., 2006). Knee laxity was also reported to be the highest level in the luteal phase of the menstrual cycle, suggesting of P 4 (progesterone) influence (Heitz et al., 1999). Meanwhile, high level of E 2 was reported to cause increased ante- rior tibia dislocation in rats during pregnancy (Charlton et al., 2001). The mechanisms underlying E 2 and P 4 effects on knee laxity are not well understood, however evidences suggested that these effects could be mediated via changes in collagen turnover (Song et al., 2014), modulation of enzymes activity involved in collagen metabolism (Shan et al., 2013) as well as response of tissues toward relaxin via changes in the amount of receptor expressed (Dehghan et al., 2014a,b). The effect of sex-steroids is preceded by the binding to intracellular receptor, located either in the cytosol or nuclear compartments (Bayard et al., 1978). Binding of ligands to this receptor will initiate translocation of ligand–receptor complex to http://dx.doi.org/10.1016/j.etap.2015.09.004 1382-6689/© 2015 Elsevier B.V. All rights reserved.