Summary
In antidiuretic rats plasma urea concentration (P u )was elevated up to 35 mM by intravenous urea loading. In renal cortical tissue (T) water content and unlabeled (u) and 14-C-urea (u *) were determined.
Water content of total renal cortex and of superficial and juxtamedullary layers were not significantly different and were not changed by the elevation ofP u .
In the control group (P u <10 mM), bothT/P u (3.06±0.71;n=29) and plasma specific activity were significantly higher than values forT/P u * (2.20±0.57;n=12) and tissue specific activity, respectively.T/P u andT/P u * were decreased significantly to the same level (1.68±0.35;n=20 and 1.51±0.21;n=7, respectively) atP u >20 mM and plasma and tissue specific activity became equal.
Deproteination of tissue homogenates did not depress 14-C-activity.
JuxtamedullaryT/P u was significantly higher than superficialT/P u .The difference was independent ofP u .
The data suggest, that renal cortical tissue urea concentration is determined (i) by distal tubular fluid urea concentration, which is inversely correlated withP u and (ii) by a constant amount of urea in an extraluminal compartment not readily exchanging.
The mechanism by which urea concentration in this extraluminal compartment is maintained independent ofP u might be urea neogenesis or urea binding to cellular structures or proteins.
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Schad, H., Reinhardt, H.W. & Armsen, T. Analysis of cortical urea sequestration in rat renal tissue slices. Pflugers Arch. 346, 31–38 (1974). https://doi.org/10.1007/BF00592648
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DOI: https://doi.org/10.1007/BF00592648