Intrarenal distribution of blood flow in rats determined by 125I-iodoantipyrine uptake.

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Abstract
Local renal blood flow was estimated in pentobarbital-anesthetized rats with 125I-iodoantipyrine (Ap) according to the method of Kety. Arterial blood was sampled continuously on rotating filter paper during 9- to 16-s i.v. Ap infusion; 1-s blood sample volumes were determined from their Hb content. After snapfreezing the kidneys, 1- to 6-mg samples were cut out from outer and inner half of cortex (OC and IC) and outer and inner half of outer medulla (OM1 and OM2). Ap concentration and blood flow were determined in 20-30 tissue samples in each experiment. A tissue-blood solubility ratio (partition coefficient) for Ap of 0.97 ml/g was determined in vivo by infusing Ap i.v. at decreasing rate for 80 s. Blood flow within each zone appeared remarkably homogeneous. After correction for methodological errors estimated from partition experiments, the coefficient of variation averaged 7.0% and 10.6% in OC and IC, respectively, obviously including errors due to inconsistent zonal dissection. Average zonal flow (ml/min per g) in 13 rats was OC, 7.09 .+-. 1.13 (SD); IC, 4.65 .+-. 0.83; OM1, 2.17 .+-. 0.37 and OM2, 0.89 .+-. 0.25. Average renal blood flow (RBF) was calculated at 4.62 ml/min per g, and the relative flow fractions of OC through OM2 at 65, 28, 6.5 and 1.6% of RBF. The high flow in IC compared to published data on microsphere uptake suggests that peritubular capillaries in this zone are partly fed by efferent arterioles of more superficial layers, and/or that microsphere uptake underestimates flow in deep glomeruli.