, Volume 346, Issue 1, pp 31-38

Analysis of cortical urea sequestration in rat renal tissue slices

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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.

Parts of this study were presented at the 35 th meeting of the Deutsche Physiologische Gesellschaft [8]