The role of A 3 adenosine receptors in central regulation of arterial blood pressure

1 Pharmacological studies have suggested that A 3 receptors are present on central neurons. Recently this adenosine receptor subtype has been identified in the rat and its presence in the central nervous system has been confirmed. 2 In this study we investigated the effects of acute intracerebroventricular (i.c.v.) injections of N 6 ‐2‐(4‐aminophenyl)‐ethyladenosine (APNEA), a non‐selective A 3 adenosine receptor agonist, on arterial blood pressure (ABP) and heart rate (HR), after treatment with 8‐cyclopentyl‐1,3‐dipropylxanthine (DPCPX), a selective antagonist of A 1 adenosine receptors. 3 Anaesthetized rats, after DPCPX (12 μg −1  kg i.c.v.), were treated with APNEA (0.4–4 μg kg −1 i.c.v.) resulting in a transitory and dose‐dependent decrease in arterial blood pressure without a change in heart rate. APNEA also induced hypotensive responses after i.c.v. pretreatment with aminophylline, at a dose of 20 μg kg −1 . In contrast, pretreatment 48 h before, with 4 μg kg −1 i.c.v. of pertussis toxin reduced the hypotensive effect induced by APNEA. Administration of APNEA at a higher dose (20 μg kg −1 i.c.v.), after DPCPX, induced a decrease in ABP of −66±5.4 mmHg and after 3 min a decrease in heart rate of −62±6.0 beats min −1 . Transection of the spinal cord abolished this significant fall in ABP, but not the decrease of HR. 4 These results suggest that a population of A 3 ‐receptors is present in the CNS, whose activation induces a decrease in blood pressure with no change of heart rate.British Journal of Pharmacology (1998) 125 , 437–440; doi: 10.1038/sj.bjp.0702126