IMPORTANCE OF NITRIC-OXIDE AND PROSTAGLANDINS IN THE CONTROL OF RAT RENAL PAPILLARY BLOOD-FLOW

The role of nitric oxide and prostaglandins in the control of rat rena l papillary blood flow has been studied in anesthetized Munich-Wistar rats by use of laser Doppler flowmeter. Acute administration of N-omeg a-nitro-L-arginine methyl ester (L-NAME) 10 mg/kg IV (n=8) increased m ean arterial pressure by 27.8+/-3.6%, decreased papillary blood flow b y 39.4+/-3.8%, and decreased renal blood flow by 47.4+/-1.9%. The subs equent administration of indomethacin (7.5 mg/kg IV) further decreased papillary blood flow (35.2+/-2.5%) without significant changes in mea n arterial pressure or renal blood flow. In a second group (n=6), admi nistration of indomethacin before L-NAME decreased papillary blood flo w by 39.6+/-2.1% without significantly altering mean arterial pressure or renal blood Row. The subsequent injection of L-NAME further decrea sed papillary blood flow (32.9+/-1.8%) and renal blood flow (49.8+/-6. 6%) while increasing mean arterial pressure to a level not significant ly different from that found in the first group. Autoregulation studie s 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 t he renal perfusion pressure-papillary blood flow relationship because L-NAME and indomethacin significantly decreased this relationship in a n additive fashion. Although both drugs reduced the sensitivity of the pressure-papillary Row relationship, only L-NAME affected autoregulat ion so that papillary blood flow was autoregulated at higher renal per fusion pressures. Thus, the present results indicate that both nitric oxide and prostaglandins control a similar percentage of rat renal pap illary blood flow, but nitric oxide seems to be more important than pr ostaglandins as a mediator of the pressure-blood flow relationship. In contrast, only nitric oxide modifies the renal blood flow level, alth ough it does not disturb whole-kidney blood flow autoregulation.