Age-related differences in the metabolism of proteoglycans in bovine articular cartilage explants maintained in the presence of insulin-like growth factor i

Articular cartilage explants from bovine calf and steer were cultured for up to 19 days in medium with or without 20% fetal bovine serum (FBS) or insulin-like growth factor I (IGF-I). Lower concentrations of IGF-I were required for maximal stimulation of PG synthesis in calf than in steer. In calf, but not in steer, IGF-I was as effective as 20% FBS in stimulating PG synthesis. The stimulation by IGF-I or FBS was not accompanied at either age by alterations in the composition of the aggregating PGs nor by changes in the proportions of CS-rich and CS-poor PG subpopulations. In calf, IGF-I and FBS did not markedly alter the rate of turnover of either the ³⁵S-PGs synthesized in vitro or the unlabeled PGs. In steer, explants cultured in the absence of IGF-I or FBS exhibited very fast rates of turnover and depletion of matrix PG with time; IGF-I and FBS were both effective in reducing the turnover rate of ³⁵S-PGs and unlabeled PGs and in preventing PG depletion.