Extraction Methods for the Determination of Regional Renal Blood Flow

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Abstract
To permit determinations of the single nephron filtration fraction at vavarious levels of the cortex of the rat kidney, methods for single glomerular blood flow measurements were evaluated. Simultaneous measurements of the medullary blood flow were made with the different test substances. Intra-aortic slug injections of radioactive microspheres, 86-rubidium and 131-I-antipyrine were given in rats. The two kidneys were clamped 10 s after the injection, the pedicles were ligated and the kidneys were removed and deep-frozen. A reference arterial blood sample was drawn continuously during the 10-second period. In another series microspheres and 131-I-albumin were injected. The radioactivity of tissue samples and reference blood samples was analysed and the blood flow of cortical and medullary regions was calculated. The microspheres gave a blood flow of 6.65 ul/mg in outer cortex, 8.15 in mid-cortex and 4.91 ul/mg in inner cortex. Corresponding values with rubidium were 4.32 ul/mg, 4.56 ul/mg and 3.86 ul/mg and with antipyrine 2.14 ul/mg, 2.28 ul/mg and 1.97 ul/mg. In the outer stripe of the outer medulla a blood flow of 1.65 ul/mg was obtained with rubidium, 1.08 ul/mg with antipyrine and 0.75 ul/mg with labelled albumin. The corresponding values in the inner stripe of the outer medulla were 1.04 ul/mg, 0.66 ul/mg and 1.01 ul/mg and in the inner medulla 1.04 ul/mg, 0.66 ul/mg and 1.23 ul/mg. It is concluded that the microsphere technique gives the most reliable results for determination of the glomerular blood flow, but that both antipyrine and rubidium - although giving too low values - reflect the distribution pattern of blood flow within the cortical region. Rubidium seems to measure the blood flow reliably in all parts of the medulla and labelled albumin in the inner stripe and in the inner medulla.