The capacity of chondrocytes to respond to serum is enhanced by organ culture in the absence of serum, stimulated by serum, and modified by ascorbate.

Cartilage slices maintained in organ culture have been shown to develop an enhanced capacity to respond to serum. The response was measured at the initiation of culture and after 3 and 7 days of culture in medium containing an inhibitor of DNA synthesis and 0, 1, or 16% serum. At these times, cartilage slices were washed to remove serum and inhibitor, and then exposed to various concentrations of serum for evaluation of DNA and proteoglycan synthesis. The range of the derived dose-response curves and the indicated sensitivity to low serum concentrations were the parameters used to evaluate the response capacity. Response capacity increased gradually, reaching a maximum after 8 days of culture. Considerable enhancement was obtained after maintenance in the absence of serum using both DNA and proteoglycan synthesis as markers. Additional, graded enhancement of response capacity was obtained when the cartilage slices were maintained in 1 or 16% serum. The effects of maintenance in serum were much greater when DNA synthesis rather than proteoglycan synthesis was used to measure the response. However, this serum-dependent enhancement was only prominent when ascorbate was present during the dose-response assay. Ascorbate caused a similar but less-marked increase in sensitivity to serum when proteoglycan synthesis was measured. The possibility that ascorbate may function as a cofactor during the progression phase of cell proliferation is discussed.