Summary
We previously described a high molecular weight fraction of human urine that causes diuresis and natriuresis in sodium depleted rats. In the present study the site of action of this fraction was investigated in hydropenic rats using micropuncture. I.v. injection of 100 µg/kg body weight of the urine extract caused a significant increase in both urinary sodium and water excretion. The rise in urinary sodium excretion wasdue mainly to a rise in water excretion. Negative free water clearance (TcH2O) decreased significantly following injection of the extract. No change in late proximal and early distal TF/P inulin and TF/P Na+ was observed indicating that fractional sodium and water reabsorption by the proximal tubule and the loop of Henle were not influenced by the extract. Total GFR, and superficial single nephron GFR remained constant. In a second study the urine extract was tested for effects on Na+ transport by frog skin. Potential difference and short circuit current were not affected by the extract even after separating the epithelium from the corium by use of collagenase. The data suggest that the extract has no direct inhibitory effect on Na+ transport by rat surface tubules and frog skin. The diuresis may be explained by a decrease in fractional free water reabsorption presumably caused by an increase in medullary blood flow.
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This work was presented in part before the V. International Congress of Nephrology, Mexico-City, October 8–13, 1972.
The investigation was supported by Deutsche Forschungsgemeinschaft (Stu 67/II).
We thank Miss Ch. Ressel for technical assistance.
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Stumpe, K.O., Pöhler, E. & Krück, F. Diuretic activity in human urine: Lack of action on proximal tubule and frog skin sodium transport. Res. Exp. Med. 162, 323–332 (1974). https://doi.org/10.1007/BF01851703
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DOI: https://doi.org/10.1007/BF01851703