Changes in serum and urinary amino acids after the administration of a mixed beta-adrenergic agonist

The administration of the repartitioning agent metaproterenol, with affinity for beta 1- and beta 2-receptors, induced marked increases in gastrocnemius muscle and heart weights. The renal loss of essential amino acids was reduced in animals treated with beta-adrenergic agonists and a significant reduction in total serum amino acids was found as well. The assessment of urinary 3-methylhistidine suggests, that those changes were accompanied by a lower myofibrillar protein breakdown, while hydroxyproline output was increased as an indirect index of collagen turnover.