Abstract 729: Spontaneous Development of Left Ventricular Hypertrophy and Diastolic Dysfunction in Mice Lacking All Nitric Oxide Synthases
Background: Nitric oxide (NO) is synthesized by three NO synthases (NOSs); nNOS, iNOS, and eNOS. We have recently succeeded in developing mice lacking all three NOS genes (triply n/i/eNOS−/− mice) (PNAS 2005). In this study, we examined cardiac morphology and function in those mice.
Methods: Experiments were performed in male wild-type (WT), singly nNOS−/−, iNOS−/−, eNOS−/−, and triply n/i/eNOS−/− mice at 2 and 5 months of age (n=5 each). Left ventricular (LV) wall thickness and LV function were analyzed by echocardiography. Cardiac fibrosis was assessed by Masson-trichrome staining.
Results: At 2 months of age, no significant cardiac morphological or functional changes were detected in any strain studied. However, at 5 months of age, significant LV hypertrophy (posterior wall thickness, mm) were noted in triply n/i/eNOS−/− (1.3±0.1, P<0.01) and eNOS−/− mice (1.1±0.1, P<0.05), but not in nNOS−/− (0.8±0.1) or iNOS−/− mice (1.0±0.1), as compared with WT mice (1.0±0.2). Importantly, the extent of LV hypertrophy was significantly greater in the triply n/i/eNOS−/− than in the eNOS−/− mice (P<0.05). LV diastolic dysfunction (as evaluated by echocardiographic E/A ratio), with preserved LV systolic function (assessed by ejection fraction), were noted only in the 5-month-old triply n/i/eNOS−/− mice (2.7±0.1, P<0.05), but not in any singly nNOS−/−(2.1±0.2), iNOS−/− (2.0±0.1), or eNOS−/− mice (2.0±0.3), as compared with the WT mice (1.9±0.1). In addition, cardiac fibrosis (fibrosis area, %) were also significantly observed only in the 5-month-old triply n/i/eNOS−/− mice (1.4±0.2, P<0.05) compared with the WT mice (0.3±0.1). Arterial blood pressure (mmHg) was significantly elevated in the triply n/i/eNOS−/−(143±3.1, P<0.05) than in the WT mice (104±7.3), but the hypertensive level was comparable to that in the eNOS−/− mice (140±8.5 P<0.05), suggesting that mechanism(s) other than hypertension was involved in the cardiac abnormalities seen in the triply n/i/eNOS−/−mice.
Conclusions: These results provide the first evidence that genetic disruption of all NOSs results in LV hypertrophy and diastolic dysfunction in mice in vivo in a hypertension-independent manner, suggesting the pivotal role of NO in the maintenance of cardiac homeostasis.