COORDINATION OF NUTRIENT USE BY PERIPHERAL-TISSUES

The growth of peripheral tissues reflects the combined effect of endogenous and exogenous signals. Limits of endogenous signals are determined by genetics, which define a chronology of growth of individual tissues. Fractional synthesis rate of muscle also follows a chronology. Endogenous mediators are both systemic and local, with tissue response a product of combined effects. Exogenous signals derive from the environment and dietary intake. Exogenous somatotropin or beta-adrenergic agonists change endogenous genetic limits for protein deposition and change partition of absorbed amino acids by stimulating anabolic use of amino acids in peripheral tissues and decreasing catabolism. Peripheral tissues provide a valuable model to study the relationships between tissues and the complexity of in vivo regulation. Shifts in metabolism of nitrogenous compounds by the liver are an example of directed changes in nutrient partitioning that act to increase supply of amino acids to peripheral tissues in conjunction with a stimulus to increase anabolic amino acid use. Further studies should integrate tissue changes with intracellular mechanisms.