Hormonal regulation of human protein metabolism.

This review focuses on the effects of hormones on protein kinetics in humans. Most of the recent knowledge on the regulation of protein metabolism in humans has been obtained by tracing protein kinetics in vivo, using labelled isotopes of essential or non-essential amino acids. This technique allows the rates of the whole-body protein synthesis and breakdown to be estimated together with amino acid oxidation and the fractional synthetic rates of mixed muscle proteins or of single plasma proteins. Changes induced within these parameters by hormonal administration or endocrine diseases are also discussed. Hormones, on the basis of their net effect on protein balance (protein synthesis minus protein breakdown), are divided into two categories: those provided with an anabolic action and those with a prevalent catabolic action. The effects on protein metabolism of the following hormones are reviewed: insulin, growth hormone, IGF-I, adrenaline, androgens, estrogens, progesterone, glucagon, glucocorticosteroids, thyroid hormones. The review concludes with a report on the effects of multiple hormonal infusions on whole-body protein kinetics and a discussion on the potential role played by the concomitant increase of several hormones in the pathogenesis of protein wasting that complicates stress diseases.