Distribution of cortical blood flow was measured in the dog by a technique based on radionuclide-labeled microspheres. Initially it was necessary to test possible pitfalls of this technique. Completeness of trapping in the kidney, the effect on renal function, and the notion that microsphere distribution reflects blood flow distribution in the kidney cortex were studied. Renal vein blood contained less than 0.2% of the microspheres (16.8^t diameter) found in the renal artery after an aortic injection. No impairment of C rAH (control 167 ± 4; postinjection 179 ± 31 ml/min), C In (control 39.3 ± 6; postinjection 37.6 ± 2 ml/min), and T m glucose (control 90.8 ± 13; postinjection 102 ± 24) was found using doses adequate to measure renal blood flow (5 mg/injection X 4 injections). After 4 injections of 50 mg each significant impairment of renal function was observed. Intrarenal blood flow distribution was determined during hemorrhagic hypotension. 3( li) Yb-labeled microspheres were injected into the root of the aorta before, and 85 Sr-labeled microspheres after, acute hemorrhage. Radioactivity was measured in the outer two thirds and inner one third of kidney slices. Tissue blood flow was calculated and expressed as the ratio of outer cortex to inner cortex counts. Renal blood flow was redistributed to the inner cortex after hemorrhage (ratio before, 3.00; after 1.30, P<0.01). Finally, the results of this technique were compared to a widely used method of measuring intrarenal blood flow distribution, 133 Xe washout. The first component of the washout technique correlated fairly well with total cortical flow but it was not possible to match the second component with any single anatomical area of the kidney. Limitations of the 138 Xe washout are discussed.
KEY WORDSshock kidney blood flow radioactive washout renal blood flow distribution radionuclide-labeled microspheres• Interest in the relationship between renal sodium metabolism and intrarenal blood flow distribution has led to the development of a variety of techniques for measuring intrarenal blood flow (1-4). One of the most recent and widely reported methods is based on the principle of compartmental analysis of a tracer ( m Xe, 85 Kr) washout curve (4). This method has the advantage of being nondestructive and can be performed repeatedly. However,
The effect of acute hypotensive hemorrhage on the intracortical distribution of renal blood flow was studied in anesthetized mongrel dogs with radioactive microspheres. In the early stages of shock, when carotid artery manipulation was avoided, outer cortical blood flow fell drastically and juxtamedullary flow was relatively well preserved. Carotid artery cannulation caused a redistribution of blood flow within the kidney even before hemorrhage, presumably by stimulating the carotid sinus reflex. Subsequently, with hemorrhage there was a parallel reduction in outer cortical and juxtamedullary blood flow. 138 Xe washout curves agreed with the microsphere findings. It was concluded that when the carotid artery was not disturbed, juxtamedullary blood flow was selectively preserved in the early stages of acute hypotensive hemorrhage.
KEY WORDSmicrospheres 133 xe washout carotid sinus reflex sympathetic nerves redistribution of intrarenal blood flow renal medullary blood flow renal cortical blood flow
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