Effects of cortisol on cell proliferation and proteoglycan synthesis and degradation in cartilage zones of the calf costochondral growth plate in vitro with and without rat plasma somatomedin activity.

The actions of cortisol were investigated in vitro on separated zones of cartilage from the calf costochondral junction, and from the structural costal cartilage. Cortisol had no direct effect in plasma-free medium on the uptake of [3H]thymidine, [3H]leucine or [35S]sulphate in any zone of growth plate or structural cartilage until pharmacological concentrations (10(-4) -10(-3) mol/1) were present, when the incorporation of all three isotopes was significantly reduced. In the presence of a somatomedin stimulus of normal rat plasma the addition of cortisol at supraphysiological concentrations (10(-8) -10(-6) mol/1) had no effect on the incorporation of any isotope in structural cartilage, but significantly reduced the uptake of [3H]thymidine in the growth plate region of proliferating chondrocytes, and at a concentration of 10(-6) mol/1 appeared to increase the uptake of [35S]sulphate in the region of maturing chondrocytes. This was not accompanied by a general increase in protein synthesis as assessed by [3H]leucine incorporation, and could reflect the decreased rate of proteoglycan degradation in the presence of cortisol. It could not be proven in the present experiments that the actions of cortisol at supraphysiological levels were dependent on the presence of growth hormone dependent somatomedin.