Juxtamedullary Afferent Arteriolar Responses to P1 and P2 Purinergic Stimulation

We assessed the responsiveness of rat juxtamedullary afferent arterioles to purinergic stimulation using the in vitro blood-perfused juxtamedullary nephron technique combined with videomicroscopy to allow direct measurement of arteriolar inside diameter. To minimize the contribution of endogenously formed angiotensin II, all rats were pretreated with enalaprilat (2 mg i.v.) for 3d minutes before the right kidney was isolated and prepared for study. Renal perfusion pressure was set at 110 mm Hg and held constant Afferent arteriolar diameter averaged 20.9±0.8 μm (n=41) under control conditions. Exposure to 1.0 μM 2-chloroadenosine induced a significant (11.1 ±3.2%) reduction in vessel diameter, whereas a 100 μ:M concentration induced an afferent vasodilation (7.6±1.5%;pμ0.05). These data are consistent with the preferential stimulation of high affinity constrictor adenosine receptors (A1) at lower concentrations and activation of lower affinity vasodilator adenosine receptors (A2) at higher concentrations. In contrast, ATP elicited a significant afferent vasoeonstriction of approximately 9.2%, 12.9%, and 10.0% at concentrations in the range of 1–100 μM (p