THE ROLE OF BETA(1) AND BETA(2) ADRENOCEPTORS IN ISOPROTERENOL-INDUCED DRINKING

The present study examined the contribution of beta(1) and beta(2) adr enoceptor activation to drinking behavior and the stimulation of plasm a renin activity produced by the mixed beta adrenoceptor agonist, isop roterenol. The stimulation of drinking by beta adrenoceptor activation could occur via two independent pathways; by either directly stimulat ing renal beta(1) adrenoceptors on the juxtaglomerular cells to releas e renin or by stimulating vascular beta(2) adrenoceptors that would de crease blood pressure and activate afferent neural and humoral mechani sms. Selective pharmacological antagonism of each adrenoceptor type wa s achieved by administering atenolol (2.5 mg/kg), a beta(1) adrenocept or antagonist, or ICI 118,551 (1 mg/kg), a beta(2) adrenoceptor antago nist, before treatment with isoproterenol (25 mu g/kg). Neither adreno ceptor mechanism alone could account for all of the water intake or st imulation of plasma renin activity due to isoproterenol treatment. Car diovascular recordings confirmed the selectivity of the antagonists to their respective receptor subtypes, with atenolol blocking the beta, adrenoceptor-mediated heart rate increases and ICI 118,551 blocking th e beta(2) adrenoceptor-mediated depressor response to isoproterenol. T he results provide evidence that the stimulation of both beta(2) and b eta(2) adrenoceptors by isoproterenol acts in a synergistic manner to induce drinking and renin-angiotensin system activation.