Coordinate regulation of collagen and proteoglycan synthesis in costal cartilage of scorbutic and acutely fasted, vitamin C-supplemented guinea pigs

Abstract

The effects of ascorbic acid deficiency and acute fasting (with ascorbate supplementation) on the synthesis of collagen and proteoglycan in costal cartilages from young guinea pigs was determined by in vitro labeling of these components with radioactive proline and sulfate, respectively. Both parameters were coordinately decreased by the second week on a vitamin C-free diet, with a continued decline to 20–30% of control values by the fourth week. These effects were quite specific, since incorporation of proline into noncollagenous protein was reduced by only 30% after 4 weeks on the deficient diet. The time course of the decrease in collagen and proteoglycan synthesis paralleled the loss of body weight induced by ascorbate deficiency. Hydroxylation of proline in collagen synthesized by scorbutic costal cartilage was reduced to about 60% of normal relatively early, and remained at that level thereafter. Neither collagen nor proteoglycan synthesis was returned to normal by the addition of ascorbate (0.2 m m) to cartilage in vitro. Administration of a single dose of ascorbate to scorbutic guinea pigs increased liver ascorbate and restored proline hydroxylation to normal levels by 24 h, but failed to increase the synthesis of collagen or proteoglycan. Synthesis of both extracellular matrix components was restored to control levels after four daily doses of ascorbate. A 96-h total fast, with ascorbate supplementation, produced rates of weight loss and decreases in the synthesis of these two components similar to those produced by acute scurvy. There was a linear correlation between changes in collagen and proteoglycan synthesis and changes in body weight during acute fasting, scurvy, and its reversal. These results suggest that it is the fasting state induced by ascorbate deficiency, rather than a direct action of the vitamin in either of these two biosynthetic pathways, which is the primary regulatory factor.