To determine whether growth hormone has a direct effect on skeletal tissues not mediated by somatomedins, and to better define the role of somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) in skeletal development, bovine growth plate, and rabbit articular and growth plate chondrocytes in primary culture were evaluated under a variety of experimental conditions designed to elicit growth hormone and Sm-C/IGF-I stimulation. Under none of these conditions did bovine growth plate chondrocytes respond to either homologous bovine growth hormone or heterologous hGH. Under the same conditions, these cells were highly responsive to human Sm-C/IGF-I with respect to both [3H]thymidine and [35S]sulfate incorporation, indices of mitotic and differentiated cell functions, respectively. Similarly, both rabbit articular and growth plate chondrocytes showed enhanced incorporation of [3H] thymidine and [35S]sulfate in the presence of Sm-C/IGF-I, but did not respond to either native or recombinant hGH. Cells at different stages of maturation within the bovine growth plate differed in their reaction to Sm-C/IGF-I with proliferative zone cells manifesting a greater response to the peptide than cells of the reserve zone. These results suggest that the action of Sm-C/IGF-I on growth plate and articular chondrocytes is direct and that the effect of GH on these cells is indirect. The data further suggest that within the growth plate, the transition from reserve to proliferative status is associated with an increased Sm-C/IGF-I responsiveness, a change which may contribute to the functional differences in these cells.

In order to study the effect of vitamin D., and some of its metabolites on cartilage, chondrocytes from the proliferative zone of rabbit growth plate cartilage were isolated and grown in culture. The 15 SO4 incorporation into proteoglycans extracted from the cells or into macromolecules obtained after dialysis of the culture medium was evaluated in the presence of vitamin D.i, synthetic 25-hydroxycholecalciferol (25-(0H)D.)), 24,25-and 1,25-dihydroxycholecalciferols (24,25-(OH)2D.» and 1,25-(OH) 2 D.,). At concentrations between 2.4 X 10" l3 M and 2.4 x 1(T 10 M, 24,25-(OH) 2 D.) was stimulatory. l,25-(OH) 2 D.i was also active at 2.4 X 10"" M and 1.2 X 10""' M concentrations. Higher concentrations of 25-(OH)D.) (2.5 x 10~8 M) were necessary to obtain a similar response. In contrast, vitamin D.t was inactive at concentrations ranging from 10" H M-KT 7 M. A polar derivative was obtained after incubation of chondrocytes or cartilage tissue with 25-(OH)D.i, and was presumed to be 24,25-(OH)2D.-i. This cartilage polar derivative was found to be equipotent to both synthetic and biosynthetic 24,25-(OH) 2 D3 in the cultured chondrocytes bioassay system. (Endocrinology 102: 1269 , 1978) N O EVIDENCE has been provided that vitamin D3 or its metabolites have a direct effect upon cartilage metabolism in vitro. Yet some in vivo observations suggest that vitamin D3 could be involved in cartilage metabolism. Changes in the physical properties of proteoglycan aggregates (1) and modification of radioactive sulfate fixation on autoradiography (2-4) were described in the matrix of growth plate cartilage from rachitic rats.The purpose of the present study was to investigate the effect of 25-hydroxycholecalciferol(25-(OH)D3) and two of its dihydroxymetabolites 24,25-and 1,25-dihydroxycholecalciferols [(24,25-(OH) 2 D 3 and 1,25-(OH^Da)] upon specific protein synthesis of cultured chondrocytes isolated from normal