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 marked decrease in glucose transport and lipogenesis that is the result of a pST-dependent decrease in the ability of insulin to stimulate these 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 somatotropin (ST) intracellular signal pathway(s) that mediate the biological effects of ST. These effects are chronic rather than acute as was previously believed. This pattern likely reflects that ST decreases transcription of important insulin-responsive genes such as the muscle-adipose tissue transporter gene (GLUT4) and key lipogenic enzymes.