Left ventricular hypertrophy is frequently observed in hypertensive patients and is believed to be due to the pressure overload and cardiomyocyte stretch. Three recent reports on mice with genetically engineered Na+ pumps, however, have demonstrated that cardiac
ouabain-sensitive α2-Na+ pumps play a key role in the pathogenesis of transaortic constriction-induced
hypertrophy.
Hypertrophy was delayed/attenuated in mice with mutant,
ouabain-resistant α2-Na+ pumps and in mice with cardiac-selective knockout or transgenic overexpression of α2-Na+ pumps. The latter, seemingly paradoxical, findings can be explained by comparing the numbers of available (
ouabain-free) high-affinity (α2)
ouabain-binding sites in wild-type, knockout, and transgenic hearts. Conversely,
hypertrophy was accelerated in α2-ouabain-resistant (R) mice in which the normally
ouabain-resistant α1-Na+ pumps were mutated to an
ouabain-sensitive (S) form (α1S/Sα2R/R or "SWAP" vs. wild-type or α1R/R α2S/S mice). Furthermore, transaortic constriction-induced
hypertrophy in SWAP mice was prevented/reversed by immunoneutralizing circulating endogenous
ouabain (EO). These findings show that EO and its
receptor, ouabain-sensitive α2, are critical factors in pressure overload-induced
cardiac hypertrophy. This complements reports linking elevated plasma EO to
hypertension,
cardiac hypertrophy, and failure in humans and elucidates the underappreciated role of the EO-Na+ pump pathway in
cardiovascular disease.