The purpose of this study was to compare the levels of procollagen type I messenger RNA (mRNA) in normal and healing medial collateral ligament (MCL) and anterior cruciate ligament (ACL) in a rabbit model. Our method of injury involved a surgical model with identical partial lacerations in the midsubstance of the MCL and ACL. Paraffin sections of normal ligaments, and ligaments 3, 7, 14, and 28 days postlaceration were studied by in situ hybridization to compare and follow the level of type I procollagen mRNA in the two ligaments. A complementary DNA (cDNA) probe corresponding to alpha 1(I) procollagen mRNA was labeled with [32P]d-CTP. After hybridization, autoradiography, and staining of the sections, the level of procollagen mRNA was assessed by microscopic examination. A higher level of procollagen mRNA was consistently detected in normal MCL than in normal ACL, suggesting higher collagen synthetic activity in the MCL. At the injury sites of the MCL and ACL, the levels of type I procollagen mRNA increased at all post-laceration periods, reaching its highest level at 14 days postsurgery. The MCL healing site had a considerably higher level of procollagen mRNA than the ACL healing site (i.e., injury site) at all postoperative intervals. The results demonstrate that procollagen mRNA levels in MCL tissue are higher than those in ACL tissue under normal conditions, as well as in response to injury. The differences in the procollagen mRNA levels of MCL and ACL may reflect the synthesis of collagen in these tissues, and may contribute to the differences in their healing capacities.
Animals Anterior Cruciate Ligament