Distribution of Radioisotope-Labeled Microparticles in the Renal Cortex of Dogs in Hemorrhagic Hypotension

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Abstract
Isotope-labeled microspheres with an average diameter of 15 μ and 25 μ, and isotope-labeled macroalbumin (131MA) were injected into the aorta of 26 dogs before or after the animals were bled to hemorrhagic hypotension. The localization of the microspheres was studied by microscopical examination and the intrarenal distribution of the radioactivity was measured. No significant effect of the hemorrhagic hypotension upon the distribution of radioactivity or the number of microspheres in different cortical layers was observed in normal kidneys. In surgically manipulated kidneys the hypotension provoked a relative increase of the radioactivity in the middle and juxta-medullar parts of the renal cortex. In the early phase of hemorrhagic hypotension the fraction of spheres with a diameter greater than 20 μ recovered in the glomeruli increased from zero to 6.3% when compared with normotensive animals; this indicates a dilatation of the afferent arterioles in this phase of hemorrhagic hypotension.