One of the effects of administering β-adrenergic agonists to sheep, cattle and pigs is the increase in lean mass that they experience. Therefore β-adrenergic agonists are thought to stimulate hypertrophy, reduce protein degradation, or a combination of both. The mechanisms of β-adrenergic agonists have been explored and in some species increased rates of hypertrophy have been evidenced. Other experiments show little or no effect. The reason for the lack of effects in some studies have been suggested to be methodological in nature, as the amount of skeletal muscle accretion is small and occurs slowly over a large period of time. Therefore measurements have to be subtle and the experiments well controlled in order to observe these growth effects. Further, protein degradation rates themselves may not be measured, but other markers of protein degradation may instead be selected and this may give a false picture of the true effects. The ability of β-adrenergic agonists to cause skeletal muscle gains may relate to increased blood flow in the skeletal muscle itself, something that could stimulate hypertrophy through increased delivery and accumulation of nutrients and growth factors to the muscle cells. Other mechanisms that could explain the skeletal muscle growth effects of β-adrenergic agonists include changes to the circulating levels of hormones such as insulin and thyroid hormone, or through β-adrenergic agonists stipulated changes to glucose metabolism, particularly glycolysis.
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Mersmann, H. J. 1998. Overview of the effects of β-adrenergic receptor agonists on animal growth including mechanisms of action. Journal of Animal Science. 76(1): 160-172
