The present experiments were designed to evaluate the importance of nitric oxide in the regulation of renal hemodynamics and the autoregulation of renal blood flow (RBF) in anesthetized dogs. RBF was measured by an electromagnetic flowmeter, and renal arterial pressure (RAP) was varied by an adjustable aortic clamp. The RAP-RBF relations were examined during the intrarenal infusion of saline or agents. The intrarenal infusion of L-NG-nitro-arginine (l-NNA, 40 μg/kg-min) at normal RAP decreased RBF and urine flow (UF), while the infusion of L-arginine-HCI (1 mg/kgmin) increased RBF and UF. Both agents did not affect the glomerular filtration rate and mean arterial pressure. The autoregulation of RBF was impaired during the l-NNA infusion. The L-arginine infusion did not affect autoregula-tory efficiency. When l-NNA (40 μg/kg-min) and L-arginine were infused simultaneously into the renal artery, the autoregulation of RBF was maintained. However, a higher dose of l-NNA (200 μg/kg-min) impaired the autoregulation of RBF. These results suggest that the basal production and/or the release of nitric oxide contributes to the regulation of renal hemodynamics and urine formation. During the reduction of RAP, nitric oxide may play an important role in the autoregulation of RBF.
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