Measurement of cardiac output and its distribution in rats under various sodium intakes, using 15 and 10 micron spheres

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Abstract
We estimated cardiac output and its distribution to organs using simultaneously injected 15 μm and 10 μm radioactive microspheres. This study was carried out in anaesthetised rats with high cardiac output induced by sodium loading and low cardiac output by sodium restriction. In neither group were the values of cardiac output and blood flow to kidneys, brain, heart and spleen affected by microsphere size. However, the ratio of blood flow estimated with 15 μm to that with 10 μm microspheres averaged 0.67: 0.60 for liver, 1.09: 1.10 for duodenum, 3.51: 3.52 for testes, and 1.19: 1.07 for adrenals in high and low sodium rats respectively. A significant escape of 10 μm microspheres from testicular, adrenal, and gastrointestinal vasculatures may explain such finding. With regard to the liver, this view was reinforced by the finding of comparable hepatic blood flow values with either bead size after clamping of the portal vein. Additional preferential losses of 10 μm microspheres from muscular vasculature seemed to contribute to the fractions of injected radioactivities recovered in lungs (that is 6 and 2% for 10 μm and 15 μm spheres respectively). These results suggest that in the rat blood flow data provided by 10 μm microspheres should be carefully analysed according to the organ(s) studied.
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