Differential regulation of the sodium pump alpha-subunit isoform gene by ouabain and digoxin in tissues of rats.
The effects of ouabain and digoxin on both the systolic blood pressure (SBP) and sodium pump alpha-subunit expression in some tissues of rats were compared. Normal rats were injected with ouabain, digoxin, and normal saline (NS), respectively, everyday, and indirect SBP was recorded once a week. Six weeks later, all the rats were killed, and sodium pump alpha1-, alpha2-, and alpha3-subunit mRNA levels were detected in the myocardium, kidney, adrenal gland, aortic smooth muscle, and hypothalamus by the RT-PCR method. The results showed that the SBP of rats infused with ouabain increased significantly at the end of week 6, while no difference in SBP was found between the digoxin and NS groups. The effects of ouabain and digoxin on sodium pump alpha-subunit isoform expression were also different. Myocardium: both ouabain and digoxin stimulated expression of the alpha3-isoform whereas alpha2 was unchanged. Levels of the alpha1 isoform decreased significantly in the ouabain group and decreased slightly in the digoxin group, respectively. Kidney: digoxin had the same effects as ouabain. alpha1 levels increased, but those of alpha2 and alpha3 remained unchanged. Adrenal gland: alpha2 and alpha3 levels increased, but those of alpha1 decreased in the ouabain group. alpha1 and alpha3 levels increased and those of alpha2 remained unchanged in the digoxin group. Aortic smooth muscle: both ouabain and digoxin increased alpha1 and alpha3 expression. alpha2 levels decreased in the digoxin group but remained unchanged in the ouabain group. Hypothalamus: both ouabain and digoxin stimulated alpha1 expression, while alpha2 and alpha3 levels remained unchanged. The results of this study have shown that ouabain and digoxin have the different effects on both the systolic blood pressure and expression of sodium pump alpha-subunit isoforms in some tissues in rats. Further studies on the expression of sodium pump alpha-subunit isoforms might be helpful for the understanding of the physiological role of endogenous ouabain and the molecular mechanisms involved in the pathogenesis of hypertension.