VITAMIN D AND ENDOCHONDRAL OSSIFICATION IN THE RAT AS INDICATED BY THE USE OF SULFUR-35 AND PHOSPHORUS-32

The concentration of inorganic sulfate-sulfur in the serum of vitamin D-deficient rats, 2.6 to 3.5 mg. per cent, was found to be higher than that in the serum of normal rats of the same age, 2.0 mg. per cent. No change was observed following the administration of 25 γ of vitamin D(2). In accord with the results of others, it was found that a definitely increased deposition of phosphorus in femurs and tibiae had occurred 36 to 48 hours after the administration of vitamin D(2) to vitamin D-deficient rats. An immediate increase in the uptake of sulfate by the skeleton was found using sodium sulfate-S(35). As measured by the specific activity of sulfate-sulfur in samples of chondroitin sulfate isolated from the skeletons of the vitamin D-deficient animals and from normal controls receiving equal doses of sulfur-35, the rate of synthesis of chondroitin sulfate in rachitic rats is similar to the rate in normal rats of the same age. Likewise, the incorporation of labelled sulfate into the sulfomuco-polysaccharides of the pelts was found to be equal at 12 hours to that in normal rats. Following the administration of vitamin D(2) to deficient animals an increase in the rate of synthesis of the chondroitin sulfate of the skeletons was noted. The radiochemical and radioautographic evidence suggest that there is in vitamin D-deficient rats an impaired utilization of chondroitin sulfate and that vitamin D(2) is able to accelerate this process.