The regulation of blood perfusion in the renal cortex and medulla by reactive oxygen species and nitric oxide in the anaesthetised rat

Aims: The regulation of blood flow through the renal medulla is important in determining blood pressure, and its dysregulation in pathophysiological states, such as oxidative stress, may contribute to the development of hypertension. This investigation examined the hypothesis that reactive oxygen species has both direct and indirect actions, via scavenging NO, to determine the degree of blood perfusion through the renal medulla. Methods: Groups of male Wistar rats received a renal interstitial infusion of either tempol, a superoxide dismutase (SOD) mimetic, or tempol plus catalase (tem + cat), or diethyldithio- carbamic acid (DETC) a SOD inhibitor, or L- NAME alone or L- NAME followed by DETC. Results: Medullary blood perfusion (MBP) increased by 16 +/- 1% (P < 0.05) following the renal infusion of tempol and by 35 +/- 4%% (P < 0.05) when tem + cat was infused. Cortical blood perfusion (CBP) was unchanged during the administration of tempol and tem + cat. The renal interstitial infusion of DETC reduced CBP by 13 +/- 2%, (P < 0.05) and MBP by 22 +/- 3% (P < 0.05). Infusion of L- NAME to block NOS did not change CBP but decreased MBP by 12 +/- 4%, which was (P < 0.05) less than the reduction obtained with DETC. Administration of DETC in the presence of L- NAME reduced CBP and MBP by 17 and 14%, respectively, the latter response being approximately half that obtained when only DETC was infused. Conclusions: These findings demonstrated that both reactive oxygen species and NO determined the level of MBP. The findings support the hypothesis that reactive oxygen species can act both indirectly, via scavenging of NO, and directly via H2O2 to modulate blood perfusion in the medulla.