Effect of Posthemorrhagic Anemia on the Renal Circulation of the Unanesthetized Rabbit

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Abstract
In the unanesthetized rabbit made acutely anemic by bleeding with plasma replacement, there was no change in renal blood flow (RBF), a reduction in glomerular filtration rate (GFR), and a reduction in renal vascular resistance with a fall in the filtration fraction. There was evidence of renal tissue hypoxia and reduction in renal PAH extraction ratio. The extraction ratio was 97% at a hematocrit ratio of 34.5%, 91% at a hematocrit of 11.5%, and 84% with hematocrits between 6 and 10%. The effects of carboxyhemoglobinemia at normal blood viscosity were compared with the effects of anemia; a smaller reduction in renal PAH extraction ratio was found and there was no reduction in filtration fraction. The reductions in renal vascular resistance and filtration fraction in anemia were partly reversed by breathing 100% O2, viscosity changes again being minimized. It was concluded that renal tissue hypoxia and reduction in red cell concentration contribute in varying degrees to the changes in the renal vascular bed and the PAH extraction ratio.