In the present work, the capacity of cartilage to metabolize 25-hydroxycholecalciferol was investigated. Cartilage preparations from growth plate, articular surface, rib, scapula, and ear were isolated from 3-week-old normal rabbits and chickens. Each tissue was separately incubated with tritiated 25-hydroxycholecalciferol (, x 10(-9) M) for 1-24 h. Incubations of kidney and muscle were performed simultaneously for comparison. Similarly, cultured chondrocytes isolated from rabbit growth plate and articular cartilage were incubated for 1 or 20 h in medium free of fetal calf serum. After methanol-chloroform extraction of tissues, cells, and their respective media, chloroform phases were chromatographed on Sephadex LH-20 columns. The results show that kidney and cartilage are able to convert 25-hydroxycholecalciferol into a derivative which migrates in the 24,25-dihydroxycholecalciferol region. Cartilage tissue previously boiled is unable to metabolize 25-hydroxycholecalciferol. The conversion of 25-hydroxycholecalciferol occurs with all types of cartilage and is also observed in incubations of cultured chondrocytes. In the latter, the polar 25-hydroxycholecalciferol derivative is detected as early as 1 h after addition of 25-hydroxycholecalciferol. Two findings suggest that the polar derivative of 25-hydroxycholecalciferol produced by cartilage is 24,25-dihydroxycholecalciferol: 1) the cartilage derivative and 24,25-dihydroxycholecalciferol (synthetic and biosynthetic) comigrate during Sephadex LH-20 and high liquid pressure chromatography; and 2) both the cartilage derivative and 24,25-dihydroxycholecalciferol are sensitive to periodate treatment.

The in vitro effects of vitamin D3 metabolites, parathyroid extract (PTE), purified parathyroid hormone (bPTH), vitamin A, and heparin on acid and alkaline phosphatases in rat or mouse calvaria in culture were investigated. Results show that: (a) when compared to values found in half calvaria incubated for 24 h in control medium, the bone acid and alkaline phosphatase content is significantly higher in paired halves incubated with PTE (L USP/ml), bPTH (4 x 10(-8)M), heparin (5 USP/ml), vitamin A (23 USP/ml), 25-(OH)D3 (2.5 x 10(-11) to 2.5 x 10(-8)M), 24,25-(OH)2D3, and 1,25-(OH)2D3 (2.5 x 10(-12) to 2.5 x 10(-7M); (b) the presence of 24,25-(OH)2D3 at low concentrations in the incubation medium decreases significantly the PTE, bPTH, vitamin A, or heparin induced stimulation of the phosphatase activities. This interaction is also observed when measuring beta glucuronidase and glucose-6-phosphatase activities and 45Ca release from previously labeled mouse calvaria; (c) a similar activity could not be found with 1,25-(OH)2D3 suggesting that 24,25-(OH)2D3 may have a specific role in bone metabolism.

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