Abstract 064: Purinergic P2X1 and P2X7 Receptors Activation Attenuate Angiotensin AT1 Receptors Dominance in Regulating the Preglomerular Renal Microcirculation in Angiotensin II Dependent Hypertension

Abstract

Two important mechanisms regulating afferent arterioles (AA) in angiotensin II (ANG II) hypertension are the purinergic receptors (P2R) and the angiotensin AT1 receptors (AT1R); however, the nature of the interactions between the respective receptors has not been established. Accordingly, studies were performed in rats subjected to 2 weeks of ANG II infusion (80 ng/min via osmotic minipumps) which has been shown to increase interstitial ATP and ANG II concentrations. Experiments using the in vitro isolated juxtamedullary nephron preparation allowed direct visualization of the AA. To determine the interaction between P2XR and AT1R on AA at hypertensive renal perfusion pressure, afferent arteriolar inside diameters (AAD) were measured in response to increases in renal perfusion pressure (RPP) from 100 mmHg to 140 mmHg followed by superfusion with the inhibitors (i). P2X1Ri (NF-449) 1 μM, P2X7Ri (A-438079) 1 μM and P2X1Ri 1 μM plus P2X7Ri 1 μM followed by superfusion with AT1Ri (SML-1394) 1 μM. Increases in RPP to 140 mmHg decreased AAD from 14.75±0.19 μm to 11.69±0.23 μm (n=15, P<0.05) demonstrating autoregulation. Treatment with P2X1Ri significantly increased AAD from 11.94±0.54 μm to 14.33±0.15 μm (n=5, P<0.05) and increased further to 15.33±0.33 μm by treatment with the AT1Ri to values similar to those at RPP 100 mmHg (14.88±0.39 μm). Treatment with the P2X7Ri also vasodilated afferent arteriolar but to a lesser extent (13.34±0.06 μm vs. 10.94±0.21 μm, n=5, P<0.05); and further treated by AT1Ri, AAD returned to values similar to those at RPP 100 mmHg (14.05±0.20 μm vs. 14.16 ± 0.19 μm). Treatment with P2X1Ri plus P2X7Ri significantly increased AAD from 12.2±0.13 μm to 14.76±0.12 μm (n=5, P<0.05) a value not significantly different from the value at RPP 100 mmHg (15.22±0.17 μm). Further treatment with AT1Ri after treatment with the P2X1Ri plus P2X7Ri significantly increased AAD to values higher than the value observed at treatment with P2X1Ri plus P2X7Ri (15.43±0.23 μm vs. 14.76 ± 0.12 μm, P<0.05). The results indicate that renal P2X1R and P2X7R exert dominant roles in the regulation of AAD during elevation in arterial pressure and attenuate most of the AT1R influence on AAD in kidneys from ANG II hypertensive rats.