Immunohistochemical localization of type II and type I collagens in articular cartilage of the femoral head of dexamethasone-treated rats.

The immunohistochemical localization of type II and type I collagens was examined in the articular cartilage of the femoral head of growing rats injected systemically with 5 mg kg-1 dexamethasone for 2 weeks every other day. The intensities of immunostaining for type II collagen, measured by microphotometry, was highest in the flattened cell layer and high in the hypertrophic cell layer, moderate in the proliferative cell and transitional cell layers and low in the superficial layer. After dexamethasone administration, the intensities decreased markedly in the flattened cell layer and slightly in the hypertrophic cell layer, although the decreases in other layers were negligible. The staining intensities for type I collagen were highest in the flattened cell layer, low in the superficial and transitional cell layers and very low in the proliferative and hypertrophic cell layers. After dexamethasone administration, the intensities increased markedly in the flattened cell layer and slightly in the superficial and proliferative cell layers, but did not change in the transitional and hypertrophic cell layers. Thus, dexamethasone administration caused a decrease in type II collagen and an increase in type I collagen in the matrix of the surface portion of articular cartilage. The composition of isoforms of collagen in the matrix changed after the steroid administration. The results strongly that the shift in collagen composition from type II to type I predominance is a cause of the degeneration of the articular cartilage after glucocorticoid administration.