CHARACTERIZATION OF OUABAIN-LIKE IMMUNOREACTIVITY IN HUMAN URINE

Objective To characterize ouabain-like immunoreactivity in human urine . Methods Sensitive radioimmunoassay for ouabain characterized by high -peformance liquid chromatography. Results Serial dilution of urinary immunoreactive ouabain paralleled the standard curve, but not so plasm a immunoreactive ouabain. Intravenous administration of 86 nmol (62.5 mu g) ouabain caused a rapid rise in ouabain immunoreactivity in plasm a of healthy volunteers with a maximum of 1.7 nmol/l 8 min after injec tion and returned to basal levels after 6 h. Ouabain immunoreactivity rose to 36 nmol/l in urine, suggesting that exogenously administered o uabain can be measured reliably in plasma and urine. Analytical revers ed-phase high-performance liquid chromatography (isopropanol-propanol biphasic gradient; linear acetonitrile gradient) of sample extracts be fore assay demonstrated measurable amounts of ouabain-related material only in native urine, but not in plasma. When plasma and urine were s piked with ouabain standard or normal volunteers were injected with ou abain, the assay reliably measured ouabain. Conclusion A substance clo sely related to ouabain can be detected in urine, but circulates, if a t all, in small amounts in human plasma.