Amino acid dependent and independent insulin stimulation of cartilage metabolism

Abstract

Effects of insulin on embryonic chicken cartilage in organ culture and dependence of these effects on essential amino acids were studied. In the presence of all essential amino acids, insulin increases 2-deoxy-D-glucose and .alpha.-aminoisobutyric acid uptake, increases [5-3H]uridine flux into uridine metabolites and the intracellular UTP pool, expands the size of the intracellular UTP pool, does not change the specific activity of the UTP pool, and stimulates RNA, proteoglycan and total protein synthesis. In lysine (or other essential amino acid)-deficient medium, the effects of insulin are different. While insulin stimulates incorporation of [5-3H]uridine into RNA, it does so by increasing the specific activity of the UTP pool without increasing RNA synthesis. Insulin stimulates 2-deoxy-D-glucose and .alpha.-aminoisobutyric acid uptake but no longer stimulates proteoglycan, total protein, or RNA synthesis or expands the size of the UTP pool. There may be amino acid dependent and independent effects of insulin on cartilage. Transport processes are amino acid independent, while synthetic processes are amino acid dependent.