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Nutritional regulation of protein metabolism

Departments of Surgery and Medicine, Health Sciences Center, Stony Brook University, Stony Brook, NY 11794-8191

¹ Correspondence: Health Sciences Center, T19 020 (phone: 631-444-1790; fax: 631-444-6039; E-mail: pgarlick{at}notes.cc.sunysb.edu).

Abstract

Protein homeostasis depends on the balance between protein synthesis and protein degradation. In muscle of growing animals, and in the whole body of human preterm infants, protein synthesis is especially sensitive to nutrient intake. This effect has been shown to depend on amino acid supply and insulin secretion. In healthy adults there is no growth, but although there is a need to retain protein, muscle protein synthesis appears to be less sensitive to food intake or insulin infusion. In humans, there has been much interest in the responses to pathological conditions, such as trauma and infection, when protein is lost from muscle. Much effort has been spent on strategies for reversing muscle wasting by nutritional and pharmacological means. However, nutritional support supplemented with branched-chain amino acids or glutamine has not been shown to restore protein synthesis after surgery. Although treatment of healthy subjects with growth hormone (GH) stimulated muscle protein synthesis, GH may not be effective for reversing protein wasting in AIDS patients, as it inhibited muscle protein synthesis in those patients who were most wasted, perhaps through a TNF-related mechanism. Acidosis is also a factor which is often associated with wasting, and has been shown in humans and animals to inhibit muscle protein synthesis.