Chronic Administration of .BETA.-Adrenergic Agonists Can Mimic the Stimulative Effect of Cold Exposure on Protein Synthesis in Rat Brown Adipose Tissue.

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When mammals are exposed to a cold environment for a long time, the capacity of nonshivering thermogenesis by brown adipose tissue (BAT) increases in association with the stimulation of synthesis of some specific proteins and tissue hyperplasia, which are totally dependent on sympathetic innervation to this tissue. To clarify the roles of the adrenergic mechanisms for the cold-induced protein synthesis and hyperplasia in BAT, in this study, the effects of chronic treatment with adrenergic agonists using an osmotic mini-pump were examined in rats. Continuous administration of noradrenaline or isoproterenol (β-agonist) for 10 days resulted in increased synthesis of the mitochondrial uncoupling protein and an isoform of glucose transporter (GLUT4), and tissue hyperplasia, in the same way as after cold exposure of the same duration. Phenylephrine (α-agonist) administration did not have any significant effect. Surgical sympathetic denervation completely abolished the effects of cold exposure, whereas it did not influence those of adrenergic agonists at all. These results indicate that the stimulative effects of cold exposure on protein synthesis and hyperplasia of BAT are attributable solely to the β-adrenergic action of noradrenaline secreted from the sympathetic nerves in this tissue.
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