Sodium Mobilization in the Perfused Rat Tail Artery. ∗

Abstract

Summary

The content and distribution of Na, K, and water in the rat tail artery were determined after perfusion in situ for 20 minutes with media in which 30 mEq/ liter of NaCl was replaced by equivalent amounts of lactose, KC1, or choline chloride. Inulin was used as index of the extracellular space. Equilibrium attained with choline chloride substitution could be explained entirely in terms of simple mixing in the free extracellular fluid. Equilibrium attained with lactose substitution involved a withdrawal of Na from the “cellular space.” A similar but smaller loss of Na from the cellular space was also observed with KC1 substitution but this was overshadowed by the progressive entry of K into this space. Thus the vascular tree contains, in a phase not accessible to inulin, a large pool of Na which is potentially capable of ready mobilization.