Antagonism of Reserpine-induced Hypothermia in Mice by Some β-Adrenoceptor Agonists

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Abstract
The reversal of reserpine-induced hypothermia in mice by three β-adrenoceptor agonists, terbutaline, salbutamol and clenbuterol, was examined. Terbutaline, 5 and 20 mg/kg intraperitoneally, caused a slight reversal of the hypothermia. Salbutamol, 5 mg/kg intraperitoneally, produced a pronounced and 1 mg/kg a slight reversal. Clenbuterol was very potent in reversing the hypothermic effect of reserpine with significant effect at 0.02 mg/kg intraperitoneally. Propranolol, 2.5 mg/kg intraperitoneally, and the selective β2-receptor antagonist IPS 339, 5 mg/kg intraperitoneally, almost completely antagonized the effect of clenbuterol, 1 mg/kg intraperitoneally. The β-receptor antagonist metoprolol at 5 and 25 mg/kg intraperitoneally only partially antagonized the effect of clenbuterol. Since clenbuterol is much more lipophilic than salbutamol and terbutaline, it is suggested that the reserpine reversal produced by clenbuterol is at least partially of central origin and possibly mediated by stimulation of noradrenergic β2 receptors.