Ouabain treatment is associated with upregulation of phosphatase inhibitor-1 and Na+/Ca2+-exchanger and β-adrenergic sensitization in rat hearts

Ouabain-induced hypertension enhances left ventricular contractility in rats

“…This is an interesting finding that suggests that the positive inotropic action of ouabain can be superimposed to other positive inotropic actions without blunting them. Reinforcing these results, El-Armouche et al (2004) showed in left ventricular papillary muscle from ouabain-treated rats for 4 days a sensitization for the positive inotropic effect of isoprenaline.…”

“…Our findings did not reveal changes in the relative potentiation and these results were reinforced by the fact that SERCA-2 protein expression did not change after ouabain treatment. In agreement, Müller-Ehmsen et al (2003) using cultured rat cardiomyocytes treated for 2 or 4 days with ouabain and El-Armouche et al (2004) using the infusion of this compound for 4 days in Wistar rats also showed that these treatments did not change the transduction pathway involved in calcium handling as the expression of SERCA-2a, phospholamban, calsequestrin or ryanodine receptor. On the other hand, in spontaneously hypertensive rats (SHR) the larger force increment developed by papillary muscles, when compared to controls, is abolished after treatment with ryanodine (Mill et al, 1998).…”

Low-dose ouabain administration increases Na+,K+-ATPase activity and reduces cardiac force development in rats

“…These findings were reinforced by measuring SERCA-2a and phospholamban protein expression, neither one were changed after 15 days. These results are in accordance with other reports in which sarcoplasmic reticulum activity is not modified after ouabain treatment [36,37]. On the other hand, Sagawa [38] reported that cardiac glycosides might amplify sarcoplasmic reticulum Ca 2+ release by a luminal Ca 2+ -sensitive mechanism, increasing myoplasmatic Ca 2+ concentration and enhancing cardiac contractility.…”

“…Results showed that isoproterenol increased force development in papillary muscles with similar magnitude in controls and ouabain treated groups. El-Armouche [37] showed that ouabain induced a sensitization for the positive inotropic effect of isoproterenol in left ventricular papillary muscles from rats treated with ouabain for 4 days. However, the differences in time of treatment with ouabain might explain these differences.…”

CHRONIC OUABAIN TREATMENT ENHANCES CARDIAC MYOSIN ATPase ACTIVITY IN RATS

“…However, ventricular performance during ouabain‐induced hypertension remains poorly understood. Previous studies have limited their scope of investigation to cardiac changes over a 2 or 4 day period and used isolated adult cardiomyocytes 17 and papillary muscles 18 . Increased expression of the NCX has been reported, but hypertension did not develop within this period; the onset of hypertension was after 1 week and attained a steady level after 35–45 days 2 .…”