The nutritional regulation of muscle growth and protein turnover

Abstract

The nutritional regulation of muscle growth is considered within the framework of the concept of the Anabolic Drive. This embodies the principle that nutritional requirements need to satisfy not only the organism's need for substrates for maintenance and growth, but also a need for the provision of nutrients to exert a regulatory influece on the organism which activates the various processes associated with growth. This latter action is defined as the anabolic drive and it has implications for nutritional requirements since if extra nutrient intakes are required for this function then efficiency of utilisation for growth and maintenance as assessed in traditional terms would be less than 100%. An example of this is human indispensable amino acid (IDAA) requirements. Most is known about the anabolic drive on muscle growth in rodents but a review of the characteristics of protein turnover in fish and rodent muscle indicates that the main features appear to be quite similar. The influence of dietary protein, insulin, T 3, and IGF-1 on rates of protein and proteoglycan turnover in muscle is reviewed, with emphasis on the extent to which the observed physiological relationships between hormone levels and target process responses are consistent with postulated mechanisms of action. It is suggested that insulin may play a pivotal role in sensing IDAA intakes and in initiating the anabolic drive through its dual role as a permissive missive stimulator of the translational phase of muscle protin synthesis at low concentrations, coupled with its stimulatory influence on the levels of T 3 and IGF-1, the latter hormones mediating increases in the capacity for protein and proteoglycan synthesis.