Importance of Nitric Oxide and Prostaglandins in the Control of Rat Renal Papillary Blood Flow

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Abstract
The role of nitric oxide and prostaglandins in the control of rat renal papillary blood flow has been studied in anesthetized Munich-Wistar rats by use of laser Doppler flowmeter. Acute administration of N ω -nitro- l -arginine methyl ester (L-NAME) 10 mg/kg IV (n=8) increased mean arterial pressure by 27.8±3.6%, decreased papillary blood flow by 39.4±3.8%, and decreased renal blood flow by 47.4±1.9%. The subsequent administration of indomethacin (7.5 mg/kg IV) further decreased papillary blood flow (35.2±2.5%) without significant changes in mean arterial pressure or renal blood flow. In a second group (n=6), administration of indomethacin before L-NAME decreased papillary blood flow by 39.6±2.1% without significantly altering mean arterial pressure or renal blood flow. The subsequent injection of L-NAME further decreased papillary blood flow (32.9±1.8%) and renal blood flow (49.8±6.6%) while increasing mean arterial pressure to a level not significantly different from that found in the first group. Autoregulation studies showed that L-NAME but not indomethacin reduced the renal perfusion pressure–renal blood flow relationship without altering autoregulation. However, both nitric oxide and prostaglandins importantly affected the renal perfusion pressure–papillary blood flow relationship because L-NAME and indomethacin significantly decreased this relationship in an additive fashion. Although both drugs reduced the sensitivity of the pressure–papillary flow relationship, only L-NAME affected autoregulation so that papillary blood flow was autoregulated at higher renal perfusion pressures. Thus, the present results indicate that both nitric oxide and prostaglandins control a similar percentage of rat renal papillary blood flow, but nitric oxide seems to be more important than prostaglandins as a mediator of the pressure–blood flow relationship. In contrast, only nitric oxide modifies the renal blood flow level, although it does not disturb whole-kidney blood flow autoregulation.