Tissue protein turnover in animals treated with the mixed beta-agonist metaproterenol: influence of dose, route and pattern of administration

Abstract

beta-Adrenergic agonists have been shown to increase protein deposition as a result of changes in the balance between protein synthesis and degradation rates. The aim of this study is to investigate the effect of the treatment with the non-selective beta-adrenergic agonist, metaproterenol, on protein metabolism in rats as well as the influence of the route and pattern of administration. A short- and long-term experimental trial were carried out. After the short-term treatment with the beta-agonist (1 mg/kg), neither protein nor nucleic acids were affected in liver or gastrocnemious muscle, while cathepsin A activity, an index of protein degradation, significantly increased in muscle. However, cathepsin A activity was reduced in muscle by the oral administration during 21 days of metaproterenol (2 ppm/day), but not by the subcutaneous injections (0.1 mg/kg/day). On the other hand, RNA/DNA, an index of protein synthesis capacity, and protein/DNA, an indicator of cell size, significantly diminished in muscle after the subcutaneous long-term treatment but did not change in the liver of treated rats. Our study has demonstrated a different outcome of a mixed beta-adrenergic agonist on protein metabolism depending on the duration of the treatment and the route of administration.