ALTERED CARDIOVASCULAR-RESPONSES TO PURINERGIC A(2) STIMULATION IN THE NUCLEUS-TRACTUS-SOLITARIUS OF SPONTANEOUSLY HYPERTENSIVE RATS

Objective: To investigate the cardiovascular effects of adenosine A(2) receptor stimulation in the nucleus tractus solitarius and whether th ese effects are altered in hypertension. Design and methods: Ten- or 1 1-week-old spontaneously hypertensive rats (SHR) or Wistar-Kyoto (WKY) rats were anaesthetized with urethane. Adenosine (100 ng) or adenosin e A(2) agonist (2-octynyladenosine, 5 ng) were micro-injected (50 nl) into the nucleus tractus solitarius. Blood pressure and heart rate wer e measured from a femoral artery. Sympathetic nerve activity was recor ded from the abdominal splanchnic nerve. Results: Blood pressure, hear t rate and sympathetic nerve activity were consistently decreased afte r the micro-injection of adenosine into normotensive rats. Changes fro m the baseline in blood pressure, heart rate and sympathetic nerve act ivity were significantly smaller in SHR than in WKY rats (blood pressu re: SHR -5.6 +/- 2.1% versus WKY rats -20.0 +/- 2.1%; heart rate: SHR -5.4 +/- 0.88% versus WKY rats -9.2 +/- 2.3%; sympathetic nerve activi ty: SHR -5.5 +/- 1.1% versus WKY rats -21 +/- 2.8%). Micro-injection o f an A(2) agonist into the nucleus tractus solitarius also decreased b lood pressure and heart rate, and those responses were not inhibited b y pretreatment with an adenosine A(1)-specific antagonist. The respons e induced by micro-injection of A(2) agonist into the nucleus tractus solitarius was significantly smaller in SHR than in WKY rats, whereas the changes in heart rate did not differ statistically (blood pressure : -23.4 +/- 4.7% versus -10.8 +/- 2.1%; heart rate: -12.1 +/- 1.2% ver sus -13.6 +/- 2.1%). Conclusion: The present results suggest that stim ulation of adenosine A(2) receptors in the nucleus tractus solitarius decreases both blood pressure and inhibitory sympathetic nerve activit y and that those inhibitory responses to adenosine in the nucleus trac tus solitarius are deranged in SHR.