Abstract 318: Uncoupled Cardiac Nitric Oxide Synthase Causes Cardiac Diastolic Dysfunction
Background: Hypertension is linked to diastolic dysfunction (DD). Hypertension and/or activation of the renin-angiotensin system (RAS) reduce vascular NO, in part, because nitric oxide synthase (NOS) becomes uncoupled with oxidative depletion of tetrahydrobiopterin (BH4).
Hypothesis: hypertension or RAS activation lead to cardiac oxidative stress, BH4 depletion, NOS uncoupling, and loss of NO that contributes to DD.
Methods: Hypertensive deoxycorticosterone acetate (DOCA)-salt mice were used to study the relation between blood pressure (BP), cardiac oxidative stress, and DD. To separate the effects of oxidation on the vasculature and the heart, selective cardiac oxidation was achieved by targeted overexpression of the angiotensin converting enzyme (ACE) gene in the heart. These ACE 1/8 mice have increased cardiac ACE, increased cardiac angiotensin II, minimal extra-cardiac ACE expression, and no hypertension. DD was confirmed by echocardiography and invasive hemodynamics. Cardiac biopterins and O2•− were measured by HPLC.
Results: Systolic BP was 114±2 v. 98±5 mmHg (p< 0.05) in DOCA v. controls. Compared to controls, DOCA mice had isolated DD based on echocardiographic measures including: LV inflow propagation velocity (49.8±2 v. 29.8±1) and E′ (5.6±0.1 v. 2.9±0.2), respectively (p< 0.01). The end-diastolic pressure-volume relation was steeper in DOCA v. controls (1.28±0.1 v. 0.67±0.1 mmHg/μl, p< 0.01) and correlated with echocardiographic indices of DD (p< 0.05). Hypertensive mice had a 53% increase in cardiac O2•−. L-NAME or the selective neuronal NOS inhibitor, 7-nitroinidazole reduced O2•− levels in DOCA (14–26%), but O2•− increased in controls (83–86%, p< 0.05). The ratio of BH4 to oxidized biopterins was lower in DOCA mice. BH4 treatment reduced cardiac O2•− by 30% and prevented or reversed DD in this model. Tetrahydroneopterin, an enzymatically inactive analog of BH4 had no effect on BP or diastolic function. Despite reducing BP, hydralazine failed to improve diastolic function in DOCA mice. Confirming a cardiac-specific effect, non-hypertensive ACE 1/8 mice showed cardiac oxidative stress and DD.
Conclusion: Depletion of BH4 and subsequent uncoupling of cardiac NOS plays a role in the development of diastolic dysfunction.