Differential Effects of Angiotensin II on Intra-Renal Hemodynamics in Rats; Contribution of Prostanoids, NO and K+ Channels

Many agents are known to cause qualitative and quantitative differences in intrarenal blood flow. This study tested the hypothesis that angiotensin II (AII) evokes a differential effect on cortical (CBF) and medullary blood flow (MBF) and that AT2 receptor mediates AII-induced increase in renal MBF by mechanisms related to nitric oxide (NO) and prostanoids. AII (100, 300 and 1000 ng/kg/min) increased mean arterial blood pressure (MABP) by 24% ± 7% (p < 0.05); decreased CBF by 30% ± 2% (p < 0.05); but increased MBF by 21% ± 8% (p < 0.05). Indomethacin (5 mg/kg), enhanced AII effects on MABP by 154% ± 26% (p < 0.05), MBF by 141% ± 46 % but decreased CBF by 74% ± 54% (p < 0.05) indicating the involvement of dilator prostanoids in the systemic and medullary circulation but constrictor prostanoids in the cortex. NG nitro-L-arginine (L-NNA), an inhibitor of NO synthase (100 mg/L in drinking water) enhanced AII effects on MABP (169 ± 75, p < 0.05) and decreased CBF (107% ± 50%, p < 0.05) but blunted the effects of AII on MBF (150% ± 21%, p < 0.05). 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ; 2 mg/kg), a guanylyl cyclase inhibitor, enhanced AII effects on MABP (118% ± 32% , p < 0.05) and decreased CBF(85% ± 47% , p < 0.05) but blunted the effects of AII on MBF (96% ± 15%, p < 0.05). However, glibenclamide (20 μg/kg), a KATP channel blocker, did not affect intra-renal hemodynamics elicited by AII. Blockade of AT2 receptors with PD123319 (50 μg/kg/min) did not change basal or AII-induced changes MABP or CBF but blunted AII-induced increase in MBF by 60% ± 11 % (p < 0.05). CGP42112 (10 μg/kg/min), an AT2 receptor agonist, elicited a reduction in MABP and increases in CBF and MBF that were abolished or attenuated by PD123319. These findings demonstrate that AII elicited differential changes in intrarenal blood flow; an AT1-mediated reduction in CBF but an AT2-mediated increase in MBF. The AT2 receptor-mediated increase in MBF involves guanylase cyclase, NO and dilator prostanoids but not KATP channels.