Divergent effects of long acting cyclic nucleotides and lysine vasopressin on the release of matrix sulfated proteoglycans into the medium of fetal rat chondrocytes in monolayer culture.

Release of sulfated proteoglycans into the medium of fetal rat chondrocytes in monolayer culture was studied by contrasting the effects of 10% calf serum, long-acting cyclic nucleotides (8 Br-cAMP or DBcAMP), and lysine vasopressin (LVP). Eight hours after initiation of the experiment, the monolayer was pulsed for 2 hours with Na2[35SO4=], the radioactivity was chased, and the monolayer was reincubated for 6 hours with conditioned medium from replicate cultures. Immediately after labelling, the amount of newly synthesized sulfated proteglycans was invariably higher in the insoluble matrix than in the medium compartment. Both additives selectively enhanced sulfate incorporation into chondroitin sulfate of the matrix when compared to serum controls, but only LVP stimulation caused increases in the medium. Remodeling (loss of cell layer and release into the medium at 6 hours) was suppressed by cAMP analogues and increased by LVP. This process was more active in cultures of lower cell density. Utilizing calibrated gel columns, no size difference of the glycosaminoglycans was found between the medium and cell layer compartments of the three treatment groups at the two time points. Because the cAMP analogues inhibit, while LVP stimulates cell division, our observations imply that the rate of degradation of the constraining matrix is increased when replication is favored, even when chondriotin sulfate synthesis is selectively stimulated.