24,25-Dihydroxyvitamin D3Antagonizes Some of the Actions of 1,25-Dihydroxyvitamin D3

The effect of 24,25-dihydroxyvitamin D3on some of the activities of 1,25-dihydroxyvitamin D3was studied in cultures of cartilage cells obtained from the tibial growth plate of rachitic chicks. The activities that were tested are those associated with intracellular exchangeable calcium, alkaline-phosphatase activity and the incorporation of thymidine and proline. 24,25-dihydroxyvitamin D3was shown in this system to antagonize the suppressive effect of 1,25-dihydroxyvitamin D3on intracellular exchangeable calcium and on proline incorporation. A similar effect on alkaline phosphatase activity and thymidine incorporation was not observed.