Adenosine has been noted as one of the endogenous modulators of renal hemodynamics. Renal hemodynamic was mainly regulated by two resistance vessels, the afferent arteriole and efferent arteriole. However, there is still no consensus as to the intrarenal vascular action site of adenosine. In this study, we examined the direct effect of adenosine on the isolated microperfused rabbit afferent and efferent arterioles. Adenosine decreased the lumen diameter of microperfused afferent arterioles dose-dependently (Control : 14.35±0.97μm, adenosine 10-7M : 12.73±1.40μm, 10-6M : 8.18±1.21μm, 10-5M : 4.33±1.16μm, n=6). Adenosine increased the lumen diameter of adenosine A1 antagonist, 8-(normantan-3-yl)-1,3-dipropylxanthin (KW-3902), pretreated-microperfused afferent arterioles preconstricted by norepinephrine. Pretreatment with adenosine A2 antagonist, (E)-1,3,-dipropyl-8-(3,4-dimethoxystyryl)-7-methylxanthin (KF-7837), enhanced adenosine induced-afferent arteriolar vasoconstrictor effect. Adenosine did not change the lumen diameter of microperfused efferent arterioles, but adenosine increased the lumen diameter of norepinephrine preconstricted-microperfused efferent arterioles. The present data suggest that the afferent arterioles possesses both adenosine A1 and A2 receptors and the efferent arterioles possesses predominantly adenosine A2 receptors at least in the rabbit kidney
