Nitric oxide synthase 2 and pressure-overload-induced left ventricular remodelling in mice

Nitric oxide synthase 2 (NOS2) has been reported to increase in hypertrophied cardiomyocytes; however, whether NOS2 plays a role in the development of hypertrophy is unknown. To investigate the relationship of NOS2 with left ventricular (LV) remodelling and hypertrophy following prolonged pressure overload, we studied 18 male wild-type (WT) and 20 male NOS2-deficient (NOS2-/-) mice before and 7, 14 and 28 days after transverse aortic constriction (TAC) using echocardiography. A subgroup of eight WT and eight NOS2-/- mice were studied 42 days after TAC. Haemodynamic measurements were obtained before killing. Left ventricular size and function were similar for both genotypes at baseline. After TAC for 28 days, both groups developed LV hypertrophy, with echo-derived LV mass increasing from 78 +/- 2 to 147 +/- 10 mg in WT and from 86 +/- 3 to 142 +/- 10 mg in NOS2-/- mice. Twenty-eight days after TAC, LV weight and cardiomyocyte width were also similar in both genotypes. Fractional shortening (FS) decreased on day 7 from 57 +/- 1 to 48 +/- 2% in WT and from 59 +/- 1 to 49 +/- 2% in NOS2-/- mice. Although this decrease in FS was transient in WT mice, it persisted in NOS2-/- mice. Invasively measured parameters of systolic and diastolic function, however, were similar in the two genotypes both 28 and 42 days after TAC. A load-independent index of contractility, Emax, was similar in both strains 42 days after TAC. In conclusion, NOS2 does not appear to have a critical role in the development of LV hypertrophy after chronic pressure overload.