OBJECTIVETo study the indexes for evaluating intervertebral disc degeneration in rats during the aging process.

METHODSNine SD rats were fed for 6 months and 12 for 22 months as the young and aged groups, respectively. The Miyamoto's grade of the rats was calculated, and the quantity and relative area of the vascular buds as well as the thickness of the calcified and non-calcified layers of the cartilage endplate were measured using the stereoscopic method. Immunohistochemistry with monoclonal antibodies was used to determine the expressions of collagens II and X in the endplate.

RESULTSThe quantity and relative area of the vascular buds, non-calcified layer/calcified layer ratio, type II collagen expression in the calcified layer and nucleus pulposus of the cartilage endplate were all significantly decreased in the aged rats as compared with those of the youth rats (P<0.05), but the collagen X expression in the non-calcified layer was significantly higher in the aged rats (P=0.003). No significant difference was found in the Miyamoto's grade between the aged and young rats (P=1.130).

CONCLUSIONThe relative area of the vascular buds, non-calcified layer/calcified layer ratio, phenotypic expressions of collagens II and X in the cartilage endplate, but not the Miyamoto's grade, are sensitive indexes for evaluating intervertebral disc degeneration in rats during the aging process.