24,25-Dihydroxyvitamin D3 antagonizes some of the actions of 1,25-dihydroxyvitamin D3.

The effect of 24,25-dihydroxyvitamin D3 on some of the activities of 1,25-dihydroxyvitamin D3 was 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 D3 was shown in this system to antagonize the suppressive effect of 1,25-dihydroxyvitamin D3 on intracellular exchangeable calcium and on proline incorporation. A similar effect on alkaline phosphatase activity and thymidine incorporation was not observed.