Radioimmunoassays, Ouabain-Like Material, and Ouabain

Abstract

To the Editor: We read with interest the article by Bauer et al1 on the changes in the plasma concentration of a ouabain-like compound associated with vigorous exercise in both humans and dogs. The authors comment on the result that is most striking to us, namely the remarkably high concentrations of the immunoassayable substance achieved without apparent ill effect. Bauer et al1 suggest that this may be a result of either the transient nature of the high concentrations measured, the “slow on-rate in forming the ouabain-Na/K ATPase complex,” or by the ouabain-like substance being bound by proteins. The most remarkable values of ouabain-like compound achieved were those in beagles with a mean “ouabain” concentration of 6882±1436 nmol/L. The raw data are not given but it is reasonable to assume that the concentration in at least one animal reached approximately 8000 nmol/L (4.68 mg/L). At such a ouabain concentration, close to 100% inhibition of any accessible sodium pumps would occur almost instantaneously. Whereas the numbers in the nontrained humans are less dramatic (176±68 nmol/L), it seems likely that the highest …