Species variation in mechanisms for modulation of growth by beta-adrenergic receptors

Beta-adrenergic agonists have been fed to avian and mammalian species to modulate growth. Such treatment produces increased rate of gain, decreased feed consumption, increased skeletal muscle and decreased fat accretion. There is good evidence for the inhibition of adipose tissue lipogenesis and stimulation of lipolysis as well as stimulation of skeletal muscle protein synthesis and inhibition of degradation. Other effects include increased blood flow and modulation of plasma concentration of various hormones. The degree to which each of these effects is observed varies considerably between experiments. Some of the diversity may be explained by species and/or tissue differences in distribution of beta-adrenergic receptor subtypes, in structure and, consequently, in response of receptors and in the pharmacodynamics of the agonist. In addition, several different agonists have been used, adding further complexity. Oversimplification by extrapolation of research observations across species and agonists may confuse attempts to derive mechanisms for the growth modulation effects of beta-adrenergic agonists in vivo.