<i>In Vitro</i>Stimulation of Leucine Incorporation Into Muscle and Cartilage Protein by a Serum Fraction with Sulfation Factor Activity: Differentiation of Elfects from Those of Growth Hormone and Insulin

Abstract

Effects of growth hormone, insulin and a serum fraction with sulfation factor activity on in vitro incorporation of (3H) leucine into TCA-insoluble protein by diaphragm and costal cartilage of hypophysectomized rats were compared. Tissues were incubated in a medium containing 14 amino acids and glucose. Cartilage was very sensitive to growth hormone in vivo but relatively insensitive in vitro. This tissue was also relatively insensitive to insulin in vitro but very sensitive to sulfation factor. Muscle was less sensitive than cartilage to growth hormone in vivo or sulfation factor in vitro. In all muscle studies combined, the maximum effect of growth hormone in vivo and the maximum effect of either sulfation factor or insulin in vitro each exceeded the maximum effect of growth hormone in high concentration in vitro. Sulfation factor in serum of normal rats was sufficient for stimulation of both muscle and cartilage from hypophysectomized rats in vitro, and the effects were not augmented by a high concentration of growth hormone and only slightly, if at all, by a high concentration of insulin. Serum of hypophysectomized rats treated with growth hormone in doses which produced in vivo stimulation of muscle and cartilage contained sulfation factor in a concentration effective on muscle and cartilage from hypophysectomized rats in vitro. Anti-insulin serum inhibited the effects of insulin but not those of sulfation factor. These findings suggest that an effect of growth hormone in vivo on protein synthesis in muscle as well as cartilage is mediated by sulfation factor. (Endocrinology 87: 1168, 1970)