β-adrenergic receptors are those that bind adrenaline or noradrenaline, and which from this binding elicit a cellular response using the G-protein coupled cyclic AMP and protein kinase A system. This system forms the CREB (cAMP response element binding protein) system. CREB is of interest because evidence suggests that CREB is able to cause expression of particular genes within specific cells, and activation of adrenergic receptors may therefore elicit longer term changes on cellular function. β-1, β-2 and β-3 are present in most mammalian tissues, but their concentrations and ratios vary between cells. Agonists of the β-adrenergic receptors that are not synthesised in animals include ephedrine, clenbuterol and amphetamine. One of the most well known effects for β-adrenergic receptors is that of causing increased lipolysis and fatty acid oxidation as well as that of stimulating the circulatory and cardiovascular system. The fatty acid oxidation effects of adrenergic receptors may stem from the high concentration of β-3 receptors in brown adipose tissue. However, a lesser known effect of adrenergic receptors is that of skeletal muscle accretion and animal studies show that adrenergic agonists such as clenbuterol can stimulate muscle growth in animals.
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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
Krief, S., Lönnqvist, F., Raimbault, S., Baude, B., Van Spronsen, A., Arner, P., Strosberg, A. D., Ricquier, D. and Emorine, L. J. 1993. Tissue distribution of beta 3-adrenergic receptor mRNA in man. The Journal of Clinical Investigation. 91(1): 344-349
