Electrolyte and Water Composition of Renal Tissue in Common Laboratory Animals. ∗

While studying rabbit renal tissue slices under a variety of conditions (1), it was observed that the medulla consistently had a significantly higher water content than the cortex. Although no published comment pertaining to this difference can be found, it would appear from data scattered in the literature(2,3,4,5,6,7) that this difference is a very frequent, if not constant, finding. In order to substantiate this impression, the water and electrolyte contents of renal tissue were determined in several mammalian species. In addition, studies were made to ascertain what changes, if any, occurred in renal tissue water content during alterations in body hydration.

Methods. Renal tissue from the following species was used: male dogs, cats, rats (Sherman), rabbits (New Zealand) and male and female guinea pigs (English). Each group consisted of 3 normal adult animals. To study altered hydration, adult male rats were placed in the following groups: (1) normal control, (2) water deprived for 5 days (food ad libitum) and (3) hydrated with 5 ml water per 100 g body weight by gavage. In the latter group, the kidneys were removed 1 and 2 hours following the gavage; the fraction of the water load which had been excreted at these times was 55 and 72 %, respectively.

The dogs, cats and rabbits were sacrificed with an overdose of intravenous Nembutal, and the rats and guinea pigs by an overdose of ether. Both kidneys were quickly removed, stripped of their capsule, and each sliced longitudinally to obtain a median sagittal section. From this section, a small sample was obtained from the cortical area and from the apical papilla. The sample was placed in a weighed 10 ml volumetric flask, and the wet weight obtained.