The involvement of nitric oxide on the adenosine A 2 receptor-induced cardiovascular inhibitory responses in the posterior hypothalamus of rats

Abstract

This study was performed to investigate the putative relationship between nitric oxide (NO) and adenosine A 2 receptors on central cardiovascular regulation in the posterior hypothalamus of rats. Posterior hypothalamic injection of drugs was performed in anesthetized, artificially ventilated male Sprague–Dawley rats. Injection of adenosine A 2 receptor agonist 5′-( N-cyclopropyl)-carboxamidoadenosine (CPCA; 1, 2 and 5 nmol) produced a dose-dependent decrease of blood pressure and heart rate. Pretreatment with adenosine A 2 receptor antagonist 3,7-dimethyl-1-propargylxanthine (10 nmol) blocked the depressor and bradycardiac effects of CPCA (5 nmol). Pretreatment with soluble guanylate cyclase inhibitor LY-83,583 (5 nmol) attenuated the depressor and bradycardiac effects of CPCA (5 nmol). In addition, pretreatment with NO synthase inhibitor N G -nitro- l-arginine methyl ester (40 nmol) attenuated the depressor and bradycardiac responses of CPCA (5 nmol). These results suggest that adenosine A 2 receptor in the posterior hypothalamus plays an inhibitory role in central cardiovascular regulation and that NO participates in the inhibitory response induced by adenosine A 2 receptor stimulation in the posterior hypothalamus.