Abstract
The changes in knee laxity and relaxin receptor expression at different phases of rodent estrous cycle are not known. Here, changes in the parameter were investigated in rats at different phases of the estrous cycle. Estrous cycle phases of intact female rats were determined by cytological examination of the vaginal smear. Following phase identification, blood was collected for serum hormone analyses. Knee passive range of motion (ROM) was determined by using a digital miniature goniometer. The animals were then sacrificed and patellar tendon, collateral ligaments and hamstring muscles were harvested for relaxin/insulin-like family peptide receptor 1 and 2 (RXFP1/RXFP2) analyses. Knee passive ROM was the highest at proestrus followed by diestrus and the lowest at estrus. Estrogen level was the highest at proestrus while progesterone and relaxin levels were the highest at diestrus. A strong correlation was observed between relaxin and progesterone levels. At proestrus, expression of RXFP1 and RXFP2 proteins and mRNAs were the highest at proestrus followed by diestrus and estrus. The finding shows that higher level of progesterone and relaxin in diestrus might be responsible for higher laxity of knee joint in rats.
Highlights
The female joint laxity has been reported to be influenced by hormones
Our findings indicate that RXFP1 and RXFP2 mRNA and protein levels were significantly higher at proestrus and diestrus compared to estrus
Our findings indicate that RXFP1 and RXFP2 mRNA and protein levels were higher at proestrus and diestrus compared to estrus
Summary
The female joint laxity has been reported to be influenced by hormones. A polypeptide hormone produced by the corpus luteum, is known to reduce the pelvic joint laxity in guinea pigs, mice and bats during pregnancy [1]. Laxity and Relaxin Receptor Expression of the Rat Knee levels were reported to correlate positively with the incidence of anterior cruciate ligament (ACL) tear, suggesting of the influence of relaxin on knee laxities [3]. The expression of relaxin receptors has been reported in humans ACL [4] and in rats, both relaxin receptor isoforms, RXFP1(relaxin family peptide receptor 1) and RXFP2 (specific ligand to insulin-like peptide 3 (INSL3) were found to be expressed in the collateral ligaments and patellar tendon [5]
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