Growth Hormone Effects on Protein Metabolism

GH has a pivotal role in regulating in vivo protein metabolism. GH was shown to enhance protein anabolism at the whole-body level, mainly by stimulating protein synthesis. It remains incompletely understood whether this important GH effect on protein synthesis occurs in all tissues. It is possible that GH's effect on protein metabolism is specific to certain proteins in a tissue rather than having a global effect on all proteins. This effect of GH may be different with acute versus chronic GH administration. These differences in the GH exposure may have different effects based not only on direct GH stimulation of protein synthesis but also the variable effects at the level of gene transcription that ultimately affect protein metabolism. Other GH effects are likely to be mediated by changes in various metabolites and hormones that probably also differ based on the duration of GH administration. GH effects on protein synthesis and breakdown probably are influenced by age as well. It is likely that GH effect on different tissues is influenced by whether it is investigated in children, adults, or the elderly. Because many of the biologic effects of GH are mediated by insulin and IGF-I, the responsiveness of these hormones to GH also may determine GH effect on protein metabolism.