This is a proposal to continue an ongoing study of the hormonal regulation of growth. Our attention will be largely directed toward somatomedin. This growth hormone dependent factor (rSm) will be isolated from the serum of rats bearing a transplantable GH secreting tumor. The feasibility of this isolation has been established in preliminary experiments. The rSm will be characterized in terms of its biologic action on cartilage and isolated fibroblasts. We will also examine a number of experimental conditions for demonstrating biologic action in vivo. In collaborative studies the amino acid composition and sequence will be determined. Radioreceptor and radioimmunoassays for rat somatomedin will be developed. Receptors for rSm in tissue will be measured and the effects of hormones and nutritional changes on the number of binding sites and affinity of binding will be determined. We will continue our studies of somatomedin generation by studying its production by isolated hepatocytes and hepatoma cells in culture. In particular, we will determine whether hormonal dependence on growth hormone and insulin can be demonstrated. We will study the binding of Sm by normal human fibroblasts and the response to Sm during different phases of cell growth. We will also compare the binding and response of normal fibroblasts with that of fibroblasts from a number of genetic diseases of growth. We will investigate the biologic action of an amniotic fluid receptor reactive material to determine whether it is a somatomedin antagonist at the cellular level.