Post-receptor actions of somatomedin on chondrocyte collagen biosynthesis

The anabolic effects of human somatomedin C on freshly isolated Swarm chondrosarcoma chondrocytes were studied. Physiological concentrations (2-34 nM) of somatomedin, but not growth hormone, stimulated the incorporation of radiolabeled precursors into collagen and non-collagen proteins, RNA and proteoglycans. The 120% increase in radiolabeling of collagen with [3H]proline by 10 nM somatomedin C was not due to changes in the rate of [3H]proline uptake. Similarly, the specific activity of newly synthesized [3H]proline-labeled collagen was not increased by 10 nM somatomedin C, indicating that changes in proline pool size or compartmentalization of [3H]proline were not involved. Somatomedin C had no effect on the rate of [3H]collagen degradation. The ability of somatomedin C to stimulate collagen synthesis was unaffected by concentrations of actinomycin D which inhibited chondrocyte RNA synthesis 90% or more. These results demonstrate that somatomedin exerts a general anabolic effect on chondrosarcoma chondrocyte metabolism. The fact that somatomedin C stimulates chondrocyte collagen synthesis in the absence of RNA synthesis suggests that this effect may be at the post-transcriptional level.