Local modulation of adrenal catecholamines release by beta-2 adrenoceptors in the anaesthetized dog

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Abstract
The release of adrenal catecholamines into the adrenal vein elicited by splanchnic nerve stimulation, was evaluated in the presence of a β-adrenoceptor agonist and both β-1 and β-2 adrenoceptor antagonists in anaesthetized and vagotomized dogs. Stimulations (0.5 V pulses of 2 ms duration for 3 min at 1 Hz) were applied before and after the i.v. infusion of the β-adrenoceptor agonist, isoproterenol (0.1 μ/kg/min). While maintaining the infusion of isoproterenol, either ICI 118551 (0.3 mg/kg), a selective β-2 adrenoceptor antagonist, or 204-155 (0.2 mg/kg), a selective β-1 adrenoceptor antagonist (Sandoz Co., Dorval, PQ, Canada), were injected intravenously and the stimulation was repeated. The results show that isoproterenol increased significantly both pre-stimulation basal levels and the stimulated release of catecholamines. These potentiated responses were significantly reversed by ICI 118551, but not by 204155. These results suggest that the release of adrenal catecholamines is locally modulated by a positive feedback mechanism through activation of β-2 adrenoceptors.