The effects of ascorbic acid deficiency on calcium and collagen metabolism in cultured fetal rat bones.

The effects of ascorbic acid deficiency on growth and calcification of bone were studied in whole 18-day fetal rat radii and ulnae cultured in a chemically defined medium. Ascorbic acid deficiency decreased the formation of labeled hydroxyporline from labeled proline in both bone shafts and cartilage ends while incorporation of tryptophan was maintained. Dry weights and collagen content of bone and cartilage were decreased, but calcification was not affected. The optimun initial concentration of ascorbic acid for collagen synthesis was 200 mug/ml. The effect of ascorbic acid was not antagonized by glucoascorbic acid or replaced by dithiothreitol. Decreased collagen synthesis in ascorbic acid deficiency could not be ascribed to loss of available peptidyl proline hydorxylase. Formation of underhydroxylated collagen and its release into the medium accounted for much of the decrease in hydroxylated collagen in ascorbic acid deficient bones. Nevertheless, the total newly synthesized collagen, as measured by collagenase digestion, was still decreased. Similar effects were exerted by alpha, alpha'-dipyridyl which also inhibited general protein synthesis. Ascorbic acid did not stimulate proline incorporation into collagen in the presence of alpha, alpha'-dipyridyl.