Growth Hormone, Insulin-Like Growth Factor-I and Lipid Metabolism: Interactions with Sex Steroids

Steroid hormones usually act via specific receptors and the hormone-receptor complex then influences the transcription of genes. These effects are often permissive for the actions of peptide hormones such as insulin and growth hormone (GH). The best known effects are those of cortisol. Since cortisol is always present, the sex steroids often modify cortisol effects. In adipose tissue, lipoprotein lipase (LPL), in the presence of insulin, is expressed via a glucocorticoid receptor, increasing transcription and stabilizing the enzyme. This process is efficiently inhibited by GH via posttranslational effects, and lipolysis is markedly stimulated. Testosterone inhibits LPL expression and, in the presence of GH, markedly increases lipolysis via multiple interactions along the lipolytic cascade. In human adipose tissue, direct effects of estrogen and progesterone cannot be demonstrated, probably because of the apparent absence of specific receptors. These hormones presumably via indirect mechanisms, perhaps by interaction with other hormone receptors.