Endogenous Na+ transport inhibitor in human hypertension: further biochemical and chemical studies

Abstract

Endogenous digitalis-like compound(s) (endalin) has(ve) been reported to be involved in some diseases. Endalin activity is increased in plasma and urine of some essential hypertensives, and in Na+-dependent experimental hypertension. The aims of this study are to compare the biological properties of one endalin extracted from urine of hypertensive patients and of normotensive offspring of hypertensive subjects to those of ouabain and to determine the chemical nature of such an urine-derived endalin. The donors were selected on the basis of the highest Na+,K+-ATPase inhibition produced by extract from their 24-h urine. They consisted of 8 hypertensive patients, 21 normotensive subjects with family history of hypertension and 6 normotensive subjects with no known family history of hypertension. Endalin was semi-purified from 500 liters of pooled urine by flash chromatography on RP 18 packing (40 microns) followed by anion exchange chromatography and two HPLCs on RP 18 reversed phase. Endalin was traced by its capability of inhibiting dog kidney Na+,K+-ATPase activity and 3H-ouabain binding to the enzyme, by its cross-reaction with anti-digoxin antibodies and by its natriuretic effect in rat bioassay. The mechanism of Na+,K+-ATPase inhibition by a semi-purified urine-derived endalin and its consequences on Na-transport were studied and compared to those of ouabain. Semi-purified urine-derived endalin was similar to ouabain in that: it reversibly and specifically inhibited Na+,K+-ATPase activity; it inhibited Na+,K+-ATPase non-competitively with ATP; its inhibitory effect was facilitated by Na+; K+ decreased its inhibitory effect on Na+,K+-ATPase.(ABSTRACT TRUNCATED AT 250 WORDS)