01019-A: Characteristics of Relaxin Expression in Dogs with Cranial Cruciate Ligament Disease

Grant Status: Closed

Grant Amount: $11,988
Dr. Wendy I Baltzer, DVM PhD, Oregon State University
September 1, 2007 - February 28, 2009
Sponsor(s): Marcia St. Lifer
Breed(s): -All Dogs
Research Program Area: Treatment

Project Summary

This research project was able to determine the expression of two relaxin genes: relaxin and the relaxin receptor RXFP2 from the hamstrings, quadriceps and cruciate ligaments of healthy intact male, female and cruciate ligament diseased male neutered and female spayed dogs. The other two relaxin genes, relaxin like factor INSL3 and relaxin receptor RXFP1 could not be isolated from these tissues. For the detectable two genes, the investigators found a significant difference in spayed female dogs with ruptured cruciate ligaments. They found the relaxin receptor RXFP2 strikingly increased in these affected spayed female dogs only in their hamstring muscles but not in the quadriceps. This finding may explain why spayed female dogs are 2.4 times more likely to develop cruciate ligament disease than intact females and why their hamstring muscles are smaller than dogs in the other groups. The increased expression of the relaxin receptor in the hamstrings of these spayed female dogs may allow increased action of relaxin on the muscle tissue. Relaxin inhibits tissue healing following injury so spayed female dogs that injure their hamstring muscles may have permanent damage to that muscle group. The weakened hamstring muscle in spayed females can no longer protect the cruciate ligament from injury from that time onward leading to chronic overuse and strain of the cruciate ligament and eventually complete rupture. Inhibition of healing of the hamstring muscle by relaxin would also explain the reduced size of the muscle compared to the other groups of dogs examined as well as the quadriceps muscles of the same spayed female dogs with cruciate ligament rupture. These findings suggest that a lack of sex hormones may predispose spayed female dogs with previously injured hamstring muscles to chronic strain and finally rupture of the cranial cruciate ligament. Further investigation into the kind of damage and resulting weakness of the hamstring muscle that occurs in spayed females as well as determining possible methods of preventing rupture of the cruciate ligament is warranted.

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