Conversion of proline U-C14 to labeled hydroxyproline by rat cartilage in vitro: effects of hypophysectomy, growth hormone, and cortisol.

Abstract

Abstract Endocrine effects on collagen synthesis have been studied by measuring the incorporation of proline into Hydroxyproline by rat cartilage in vitro. Rat cartilages were incubated in a medium containing proline-U-C 14 for 24 hours. After incubation, hydroxyproline was isolated by column chromatography from whole cartilage or extracts of cartilage homogenates. Only about one quarter of the labeled hydroxyproline of cartilage was found in mature collagen as judged by solubility properties. The remainder was solubilized either in water or dilute alkali. The water extract contained hydoxyproline of the highest specific activity. The formation of hydroxyproline was greatly decreased in cartilage from hypophysectomized rats. Growth hormone treatment of hypophysectomized rats partially restored the rate of hydroxyproline formation. Growth hormone added in vitro, however, was without significant effect. Addition of normal rat serum to the mcubation medium stimulated the rate of hydroxyproline formation by cartilage from hypophysectomized rats as compared with experiments in which hypophysectomized rat serum was added. Although cortisol treatment of normal rats did not impair the ability of isolated cartilage to form hydroxyproline, cortisol added in vitro in a concentration of 0.9 μg per milliliter did inhibit formation of labeled hydroxyproline.