Purification of a Na+/K+ ATPase inhibitor from borderline hypertensives' plasma

Increasing experimental evidences suggest an involvement of an endogenous Na+/K+ ATPase inhibitor in regulating water and electrolytes balance as well as in the pathogenesis of hypertension. However, conflicting results on the nature and the chemical structure of this substance still make it difficult to understand exactly its physiological mechanism of action. In the present study an attempt was made to purify a Na+/K+ ATPase inhibitor from hypertensives' plasma by solid phase extraction followed by 2 HPLC steps using reverse and normal phase columns. The fractions, from both columns, were able to inhibit Na+/K+ ATPase, 3H-ouabain binding to enzyme, ouabain sensitive 86Rb uptake and pNPPase activity in a manner not affected by boiling. Ultrafiltration experiments demonstrate that inhibitory activity is largely due to a low-molecular weight substance. These findings seem to confirm the presence in hypertensives plasma of a Na+/K+ ATPase inhibitor with some similarities with ouabain.