Role of adenosine A2B receptors in vasodilation of rat pial artery and cerebral blood flow autoregulation

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Abstract
This study was aimed to investigate the underlying mechanism of vasodilation induced by the activation of A2B adenosine receptors in relation to cerebral blood flow (CBF) autoregulation. Changes in pial arterial diameters were observed directly through a closed cranial window. N ω-nitro-l-arginine methyl ester (l-NAME, nitric oxide synthase inhibitor) significantly suppressed the concentration-dependent vasodilations induced by adenosine and 5′- N-ethylcarboxamido-adenosine (NECA) but not the vasodilation by CGS-21680 (A2A-receptor agonist). Moreover, NECA-induced vasodilation was suppressed by alloxazine (1 μmol/l) but not by ZM-241385 (1 μmol/l, A2Aantagonist), which suggests mediation by A2B- receptor activation. Otherwise, the level of nitrite/nitrate was concentration dependently increased in the artificial cerebrospinal fluid (CSF) when adenosine and NECA were suffused over the cortical surface.l-NAME and alloxazine, but not ZM-241385, largely inhibited their releases. The lower limit of CBF autoregulation was little affected following pretreatment with l-NAME or alloxazine. Thus it is suggested that adenosine-induced vasodilation via activation of A2B-adenosine receptors of the rat pial artery is coupled to the production of nitric oxide, which contributes little to CBF autoregulation.