Renal blood flow distribution measured by microspheres during isovolemic hematocrit alteration in rats

Abstract

The distribution of 15-μm microspheres was measured in rat kidneys before and after the animals had undergone either isovolemic hematocrit increase or isovolemic hematocrit decrease. Raising the systemic arterial hematocrit from 46 ± 1% (mean ± SEM) to 59 ± 1% caused a significant decrease in the rates of urinary sodium and potassium excretion [Formula: see text], but no significant changes in total renal blood flow (RBF), filtration fraction (FF), outer cortical flow, inner cortical flow, or rate of urinary volume excretion [Formula: see text]. Fractional sodium excretion was also unchanged suggesting that the decreased [Formula: see text] was the result of a decreased glomerular filtration rate (GFR). The measured decrease in GFR was not statistically significant. Lowering the systemic hematocrit from 45 ± 1% to 33 ± 1% caused a significant fall in FF as well as significant increases in the rate of urine volume excretion [Formula: see text], [Formula: see text], and GFR. There was a significant increase in RBF but again no change in the flow distribution between inner and outer cortex. The findings show that hematocrit alterations alone do not immediately lead to a redistribution of blood flow between inner and outer cortex of the rat kidney.