Role of alpha- and beta-adrenoceptors in sympathetically mediated thermogenesis.

This study was intended to investigate the role of alpha- and beta-adrenoceptor populations in the sympathetically mediated thermogenesis in healthy lean males. In the first study, the beta 1-, beta 2-, and beta 3-agonist isoprenaline was infused in increasing doses with and without simultaneous infusion of the beta 1-blocker atenolol (Iso and Iso+AT, respectively). There was an increase in whole body energy expenditure (EE) after infusing Iso+AT (P < 0.001) and an almost twofold higher increase after infusion of Iso only (P < 0.001). Stimulation of the beta 2-adrenoceptors by a specific agonist (salbutamol) resulted in a significant increase in EE (P < 0.001). The effect of stimulation of alpha 1-adrenoceptors on EE was measured by infusing increasing doses of the alpha 1-agonist phenylephrine. EE did not change, whereas blood pressure (BP) increased (P < 0.001) and heart rate decreased (P < 0.01). In addition to this study, the alpha 1-, alpha 2-, beta 1-, beta 2-, and beta 3-agonists norepinephrine and epinephrine were infused with simultaneous infusion of the beta 1- and beta 2-blocker propranolol. In both studies, there was no effect on EE, whereas BP increased (P < 0.01). In conclusion, in healthy male lean volunteers both beta 1- and beta 2-adrenoceptors are involved in the sympathetically mediated thermogenesis, whereas the alpha 1-, alpha 2-, and beta 3-adrenoceptors do not play a role.