Regulation of muscle protein turnover: possible implications for modifying the responses to trauma and nutrient intake.

The physiological control of muscle protein balance has been reviewed. In addition to trauma, fasting and reduced activity have been shown to cause muscle protein loss through changes in synthesis and breakdown. Many of the effects of these states are mediated by alterations in the concentrations of insulin, glucagon, steroids and catecholamines. Branched-chain amino acids also appear to have specific effects in improving protein synthesis. Recently, prostaglandins have been identified as having a central role as mediators in the control of protein metabolism by many hormones and pathological states. Identification of factors which control muscle protein synthesis leads to the possibility that the metabolic response to illness and injury and its attendant muscle protein loss could be open to pharmacological manipulation. Inhibition of prostaglandin synthesis by non-steroidal anti-inflammatory drugs can improve muscle protein turnover, but their clinical usefulness may be limited by side-effects. Hormonal manipulation may offer the possibility of abolishing the metabolic response. For example, inhibition of adrenal secretion in surgical patients by spinal anaesthesia appears to modify many of the metabolic effects of injury. A variety of other treatments have been used to minimize the metabolic derangements of injury. Some of these have considerable potential, but as yet clinical benefits from their use have not been positively identified. It is likely that a pharmacological approach to the nutritional disorders of stress and injury will prove to be of major interest in the future.