MECHANISMS BY WHICH SOMATOTROPIN DECREASES ADIPOSE-TISSUE GROWTH

When growing pigs are treated daily with recombinantly derived porcine somatotropin (pST) for 30-60 d there is a dose-dependent decrease in lipid accretion. Maximal doses of pST can reduce lipid accretion by as much as 70%. The reduction in lipid accretion occurs because of a mar ked decrease in glucose transport and lipogenesis that is the result o f a pST-dependent decrease in the ability of insulin to stimulate thes e processes in the adipocyte; lipolysis is not affected. The decrease in insulin sensitivity is not due to a decrease in insulin binding or insulin receptor kinase activity. Little is understood about the somat otropin (ST) intracellular signal pathway(s) that mediate the biologic al effects of ST. These effects are chronic rather than acute as was p reviously believed. This pattern likely reflects that ST decreases tra nscription of important insulin-responsive genes such as the muscle-ad ipose tissue transporter gene (GLUT4) and key lipogenic enzymes.