Effects of p-Adrenergic Agonists on Cellular Metabolism

Presentations at previous Reciprocal Meat Conferences (Ricks et al., 1984; Beermann et al., 1985) and the presentations immediately preceding mine have described in detail the influence of p-adrenergic agonists, such as clenbuterol, cimaterol or ractopamine, on growth and carcass traits in livestock. We now can say with some certainty that the feeding of p-adrenergic agents to livestock increases the rate of growth of muscle and decreases fat accretion. However, we are considerably more uncertain about the cellular mechanism of action of these compounds. The pronounced and highly reproducible results (at least in ruminant species) elicited by p-adrenergic agents provide animal scientists with a powerful tool for investigating the regulation of muscle and adipose tissue growth and development. It is my intent to provide a summary of the research that has been performed with swine, sheep and cattle that sheds some light on the cellular mechanisms involved in the modification of muscle and adipose tissue growth in animals exposed to p-adrenergic agents. Most of the research is quite recent, and I will depend heavily on material published at present only in abstract form. Although I will reference some of the work accomplished with laboratory species, I will focus primarily on livestock species because, as you will see, the effects we observe appear to be highly species-specific.