Water and Electrolyte Exchanges Between Excised Rabbit Tissues and Plasma

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Abstract
Freshly excised rabbit tissues did not maintain their water and electrolyte composition when immersed in vitro in plasma obtained from blood of the same animal. All gained water, chloride and sodium and, in general, lost potassium. Changes occurred with varying speed and degree for each tissue. Increases in skin appeared to be due to entrance of plasma or plasma filtrate. In tendon there were indications of a selective water imbibition, although similarities existed with skin changes. In muscle, liver and brain, chloride and sodium entered in larger proportion than explained by a plasma filtrate entrance. More sodium entered than potassium was lost with a resulting cation gain. In muscle and liver there was some evidence that sodium gain in excess of potassium loss could have been due to plasma or plasma filtrate entrance. In brain, all water and electrolyte movements seemed to be independent of each other. A relatively large proportion of the potassium content of muscle seemed to be readily exchangeable with plasma. The opposite was true for liver and brain. Control chloride and sodium tissue spaces of skin and tendon in most instances were greater than total water, a fact which made calculations of spaces of doubtful value for determining cellular and interstitial tissue fractions. Different sizes of radioactive sucrose, chloride and sodium spaces in muscle, liver and brain left the question of which was a true indicator of extracellular volume unanswered. Endogenous reductase activity measured with a tetrazolium salt was fairly well maintained after immersion in all tissues except brain, but no relationship between this activity and electrolyte composition could be ascertained. No activity was detected in tendon.
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