Influence of oxygen tension on somatomedin activity in vitro.

Somatomedins are the intermediaries through which growth hormone acts on the epiphyseal growth plate to effect linear skeletal growth. Rat epiphyseal chondrocytes were isolated and cultured in vitro in the presence of somatomedin. Two sources of somatomedin were used, foetal calf serum and rat liver perfusates. The chondrocytes proliferated and synthesized sulphated glycosaminoglycans when grown in the presence of somatomedin from either source, but were not metabolically active in chemically defined medium alone. Some differences in the growth patterns in response to serum or liver somatomedins are reported and discussed. Chondrocyte metabolic activity in the presence of somatomedin in vitro showed a graded response to alterations in the atmospheric oxygen, being greatest at low oxygen pressure, and almost completely inhibited at 95% oxygen. A gradient of local oxygen tension has been reported to exist across the epiphyseal plate in vivo. The effects of somatomedin combined with changing oxygen levels may help to explain the divergence of cell proliferation and matrix synthesis seen in the various regions of the growth plate.