The administration of metaproterenol induced an increase in gastrocnemius muscle weight without change in body growth rate or tissue protein concentrations, while epididymal fat was reduced. This effect was accompanied by an enhancement in the levels of intracellular amino acids in muscle. By contrast, liver amino acids were unaffected by treatment with the mixed beta-adrenergic agonist.

The administration of the repartitioning agent metaproterenol, with affinity for β₁ and β₂-receptors, induced marked increases in gastrocnemius muscle and heart weights. The renal loss of essential amino acids was reduced in animals treated with β-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 myofíbrillar protein breakdown, while hydroxyproline output was increased as an indirect index of collagen turnover.