The alpha2-isoform of Na-K-ATPase mediates ouabain-induced hypertension in mice and increased vascular contractility in vitro.

Although ouabain is known to induce hypertension, the mechanism of how this cardiac glycoside affects blood pressure is uncertain. The present study demonstrates that the alpha2-isoform of the Na-K-ATPase mediates the pressor effects of ouabain in mice. To accomplish this, we analyzed the effect of ouabain on blood pressure in wild-type mice, where the alpha2-isoform is sensitive to ouabain, and genetically engineered mice expressing a ouabain-insensitive alpha2-isoform of the Na-K-ATPase. Thus differences in the response to ouabain between these two genotypes can only be attributed to the alpha2-isoform of Na-K-ATPase. As the alpha1-isoform is naturally resistant to ouabain in rodents, it will not be inhibited by ouabain in either genotype. Whereas prolonged administration of ouabain increased levels of ouabain in serum from both wild-type and targeted animals, hypertension developed only in wild-type mice. In addition, bolus intravenous infusion of ouabain increased the systolic, mean arterial, and left ventricular blood pressure in only wild-type anesthetized mice. In vitro, ouabain increased vascular tone and thereby phenylephrine-induced contraction of the aorta in intact and endothelium-denuded wild-type mice but in alpha2-resistant mice. Ouabain also increased the magnitude of the spontaneous contractions of portal vein and the basal tone of the intact aorta from only wild-type mice. The increase in aortic basal tone was dependent on the presence of endothelium. Our studies also demonstrate that the alpha2-isoform of Na-K-ATPase mediates the ouabain-induced increase in vascular contractility. This could play a role in the development and maintenance of ouabain-induced hypertension.