The influence of oral and subcutaneous administration of a mixed beta-adrenergic agonist on tissue and cell growth.

The non-selective beta-adrenergic agonist, metaproterenol, administered orally (2 ppm and 20 ppm) and subcutaneously (0.1 mg/Kg/d) for 21 days to young male rats induced no changes in animal growth or food intake. However, the rats treated with metaproterenol showed increased muscle gastrocnemius weight, which was accompanied by a muscle hyperplasia (DNA content increase) and a reduction in cellular size (protein/DNA ratio decrease). The beta-agonist did not affect liver growth or liver cellularity when assessed through the nucleic acid content. The increase in muscle mass was attributed, at least in part, to a reduction in protein breakdown as muscular cathepsin A activity was significantly lower in beta-agonist treated rats.