CHANGES IN RENAL MICROCIRCULATION INDUCED BY INFUSION OF (FE3-MYOGLOBIN AND (FE2+)-MYOGLOBIN DURING HEMORRHAGIC HYPOTENSION IN THE ANESTHETIZED RAT - INFLUENCE OF L-NAME AND 8-BR-CYCLIC GMP())

The effects of myoglobin on renal microcirculation were studied in ane sthetized rats subjected to hemorrhagic hypotension. Capillary flow di stribution was determined by allowing two dyes to circulate for 3 and I min, respectively, freezing the left kidney and quantifying the dye distribution in histological sections by analyzing the distances of re gularly spaced test points to the next dye-labeled capillary. Control experiments showed 88% of distances to be <12 mu m in the cortex [medu llary outer stripe (OS): 77%, inner stripe (IS): 93%] and no distance to be >60 mu m. Myoglobin induced disturbances in intrarenal perfusion with a significantly higher potency of (Fe2+)- as compared to (Fe3+)- myoglobin. With the reduced species, the fraction of distances >60 mu m increased to 54% in the cortex (OS: 69%; IS: 67%). L-NAME, an inhibi tor of nitric oxide synthesis, induced similar defects of perfusion. T he cGMP analogue 8-Br-cGMP was able to nearly completely prevent these effects. The results support the view that myoglobin when released du ring hemorrhagic hypotension impairs renal microcirculation supposedly by scavenging the endogenous relaxing factor nitric oxide.