Effects of microinjection of adenosine into area postrema on heart rate, blood pressure and renal sympathetic nerve activity in rats

The effects of microinjection of adenosine (Ado) into area postrema (AP) on mean arterial pressure (MAP), heart rate (HR) and renal sympathetic nerve activity (RSNA) were examined in 53 anesthetized Sprague-Dawley rats. The results obtained are as follows. (1) Following microinjection of Ado (1 ng/60 nl) into AP, MAP, HR and RSNA were decreased from 13.76±0.46 kPa, 356.28±4.25 bpm and 100±0% to 11.23±0.49 kPa (P < 0.001), 336.91±5.23 bpm (P < 0.01) and 70.95±5.19% (P < 0.001), respectively; (2) 8-phenyltheophylline (150 μg/kg, 0.2 ml, iv), a nonselective adenosine receptor antagonist, and 8-cyclopentyl-1,3-dipropylxanthine (500 μg/kg, 0.2 ml, iv), a selective A₁ adenosine receptor antagonist, blocked the inhibitory effect of Ado completely; and (3) glibenclamide (5 mg/kg, 0.2 ml, iv), a blocker of ATP-sensitive potassium channel, also abolished the effect of Ado. The above results indicate that microinjection of Ado into AP induces inhibitory effects on MAP, HR and RSNA, which may be related to activation of ATP-sensitive potassium channels mediated by A₁ receptors.