A NOVEL ENDOGENOUS SODIUM-PUMP INHIBITOR IN PIG URINE - PURIFICATION AND COMPARISON WITH THE INHIBITOR PURIFIED FROM BOVINE ADRENAL-GLANDS

To clarify the chemical nature and pathophysiological significance of an endogenous, specific Na-pump inhibitor, extracts of various tissues have been examined. The activities were extracted by an Amberlite XAD -2 adsorbent and fractionated by high-performance liquid chromatograph y (HPLC) on an ODS column. Among many tissues and fractions tested, th e extract of pig urine has been found to contain a large amount of Rb- 86 uptake inhibitory activities. The strongest inhibitory activity for Rb-86 influx into erythrocytes also exhibited a cross-reactivity with anti-ouabain antibodies. This activity has been purified to homogenei ty using five steps of reverse-phase HPLC. Although most of the dose-r esponse curves for this purified Na-pump inhibitor, designated as urox in, in the various assay systems paralleled those of ouabain and the i nhibitor purified from bovine adrenal glands (designated as adrexin C) , the cross-reactivity curve with antiouabain antibodies did not. The retention time of uroxin on an ODS HPLC column was also different from that of digoxin, ouabain, or adrexin C. H-1 nuclear magnetic resonanc e spectroscopic study suggests that uroxin is a novel Na-pump inhibito r that is structurally different from any of the known cardiotonic ste roids or the substances previously reported to exhibit Na-pump inhibit ory activity. Thus, uroxin may be a new type of endogenous regulator f or the Na pump.