Renal test dyes V.

Abstract

Fluorescence intensities on the renal cortex of Wistar-Furth rats were measured photometrically after an i.v. injection of FITC-dextrans with a molecular weight of 3400, 19000, 26000, 41000 or 153000. The kidney surface was illuminated by the 488 nm line of an ionized argon laser and the fluorescent patterns were recorded by a high sensitivity television camera connected with a tape recorder. Intensities of fluorescence were evaluated directly from the television record. Passages of FITC-dextrans through peritubular capillaries, early and late proximal as well as distal tubules correspond to those of lissamine green. Intensity of the dye during the tubular passage decreases with increasing molecular weight of dextran. Comparison of the tubular intensity of dextran 19000, 26000, 35000 and 41000 with that of dextran 3400 gave corresponding values of 45%, 33%, 19% and 13%, respectively. As could be expected from clearance results, dextran 153000 was only visible during its passage through the peritubular capillaries, but no tubular passage could be observed. This method permits, for the first time, the visualization and photometric quantification of glomerular filtration as a function of molecular size, i.e. glomerular permeability. Since several tubules are seen in each recorded field, it is often possible to make several analyses from the same videotaped record. The photometry of a dye bolus also allowed the measurement of local flow velocities in the proximal tubular loops.

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