Abstract
Very little is known about the mechanism of the active secretory transport of the kidney. We have tried to attack this problem by investigating the secretory activity of the tubules of the frog kidney as regards dyestuffs, which more or less resemble one another by their molecular configuration. The isolated kidney was perfused with Ringer solution through the aorta under a pressure of about 24 cm of water and with Ringer solution containing 0.0005% of dyestuff through the renal portal vein under a pressure of about 12 cm. About 30 dyestuffs have been tested, all of them being mono-azo-sulfonic acid dyes and all of them being diffusible.
One series of experiments was concerned with 8 naphthalene-azo-naphthalene-disulfonates. The result obtained showed an obvious connection between the structure of the dye and its aptitude for secretory concentration. The main decisive feature is the location of the sulfonate groups in the molecule. If both sulfonates are on the same half of the molecule, as with Fast Violet R, Echtrot B. Acid Violet 6R and Palatine Red A, the injected dye reappears in the secretion at a higher concentration. If one sulfonate is attached to one naphthalene nucleus, the other sulfonate to the other, as in Fast Red C., Fast Red E, Serichrome Blue R and Brilliant Ponceau 4R, little or no secretion occurs. As yet, only one exception has been met, Crocein Scarlet 3BX. This dye is secreted although the 2 sulfonate groups are in opposite positions. This exceptional behavior could possibly arise from the particular location of one sulfonate with respect to the azo group. We shall come back to this point later.
In another series of experiments, 13 benzene-azo-naphthalene-sulfonates were used. Eight of them were mono-sulfonates, 5 of them di-sulfonates.
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