Free intracellular and protein bound amino acids in tissues as affected by a mixedβ-adrenergic agonist

Abstract

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.

Muscle protein waste in tumor-bearing rats is effectively antagonized by a beta 2-adrenergic agonist (clenbuterol). Role of the ATP-ubiquitin-dependent proteolytic pathway.

“…Reeds et al (42) did not observe any change in the gastrocnemius protein synthesis rates after dietary administration of clenbuterol to rats, and concluded that decreased breakdown had to be involved. An indirect confirmation that /2-agonists may act by reducing protein catabolism came from a recent study in which the intracellular amino acid content of rat gastrocnemius was shown to increase after treatment with metaproterenol (43). In addition, glutamine, and alanine were found to be released at reduced rates from isolated muscles in the presence of the,3-adrenergic agonist isoprenaline (44).…”