HORMONAL-REGULATION OF PROTEIN-METABOLISM IN RELATION TO NUTRITION AND DISEASE

This paper examines the role of hormones in the normal responses of mu scle protein synthesis to nutrient intake and the use of hormones to i mprove the effects of nutritional therapies in patients with protein-w asting conditions, in growing rats, the increase in muscle protein syn thesis after feeding seems to be mediated by the rise in plasma insuli n and also by an enhanced sensitivity of the muscle to insulin brought about by the amino acid leucine. In adult rats, however, the responsi veness of muscle to both feeding and insulin is much reduced, suggesti ng that changes in protein degradation play an important role in the r esponse to feeding, Similarly, in adult humans, muscle protein synthes is is not affected by insulin, but is stimulated by insulin-like growt h factor (IGF)-I and growth hormone (GH). The effect of GH treatment h as been studied in a number of different groups of patients suffering from protein wasting, and improvements in nitrogen balance and lean bo dy mass have been reported. In a study of patients with acquired immun odeficiency syndrome (AIDS), however, GH treatment for 2 wk caused a f all in muscle protein synthesis in the patients with wasting, despite an increase in healthy controls, suggesting that the responsiveness of muscle to the hormone may be altered by the stage of the disease.