Tissue distribution of an endogenous ligand to the Na, K ATPase molecule.

A variety of evidence indicates the presence of a circulating ligand to the Na, K ATPase molecule that is involved in the regulation of extracellular sodium metabolism. To examine the potential role of endogenous ligands to the Na, K ATPase molecule in the regulation of intracellular sodium metabolism, the tissue distribution of digitalis-like activity was quantitated in several brain regions and peripheral organs. The digitalis-like activity of desalted and delipidated extracts of tissue was widely distributed and produced a displacement of tritiated ouabain that was parallel to the displacement produced by cold ouabain. These results suggest that tissue contains an endogenous ligand to the Na, K ATPase molecule and that this ligand may regulate intracellular sodium metabolism in an autocoid-like manner.