Background Ventricular expression of phosphodiesterase-5 (PDE5), an enzyme responsible for cGMP catabolism, is increased in human right ventricular hypertrophy, but its role in left ventricular (LV) failure remains incompletely understood. We therefore measured LV PDE5 expression in patients with advanced systolic heart failure and characterized LV remodeling after myocardial infarction (MI) in transgenic mice with cardiomyocyte-specific over-expression of PDE5 (PDE5-TG). Methods and Results Immunoblot and immunohistochemistry techniques revealed that PDE5 expression was greater in explanted LVs from patients with dilated and ischemic cardiomyopathy than in control hearts. To evaluate the impact of increased ventricular PDE5 levels on cardiac function, PDE5-TG mice were generated. Confocal and immunoelectron microscopy revealed increased PDE5 expression in cardiomyocytes predominantly localized to Z-bands. At baseline, myocardial cGMP levels, cell shortening and calcium handling in isolated cardiomyocytes, and LV hemodynamic measurements were similar in PDE5-TG and wild-type littermates (WT). Ten days after MI, LV cGMP levels increased to a greater extent in WT than PDE5-TG (P<0.05). Ten weeks after MI, LV end-systolic and -diastolic volumes were larger in PDE5-TG than in WT (57±5 vs 39±4 and 65±6 vs 48±4 µL, respectively, P<0.01 for both). LV systolic and diastolic dysfunction was more marked in PDE5-TG than WT associated with enhanced hypertrophy and reduced contractile function in isolated cardiomyocytes from remote myocardium. Conclusions Increased PDE5 expression predisposes mice to adverse LV remodeling after MI. Increased myocardial PDE5 expression in patients with advanced cardiomyopathy may contribute to the development of heart failure and represents an important therapeutic target.

These findings demonstrate that sGCalpha1beta1-derived cGMP signalling has gender-specific and testosterone-dependent cardiovascular effects and reveal that the effects of NO on systemic blood pressure do not require sGCalpha1beta1.

To learn whether nitric oxide (NO) inhalation can decrease myocardial ischemia-reperfusion (I/R) injury, we studied a murine model of myocardial infarction (MI). Anesthetized mice underwent left anterior descending coronary artery ligation for 30, 60, or 120 min followed by reperfusion. Mice breathed NO beginning 20 min before reperfusion and continuing thereafter for 24 h. MI size and area at risk were measured, and left ventricular (LV) function was evaluated using echocardiography and invasive hemodynamic measurements. Inhalation of 40 or 80 ppm, but not 20 ppm, NO decreased the ratio of MI size to area at risk. NO inhalation improved LV systolic function, as assessed by echocardiography 24 h after reperfusion, and systolic and diastolic function, as evaluated by hemodynamic measurements 72 h after reperfusion. Myocardial neutrophil infiltration was reduced in mice breathing NO, and neutrophil depletion prevented inhaled NO from reducing myocardial I/R injury. NO inhalation increased arterial nitrite levels but did not change myocardial cGMP levels. Breathing 40 or 80 ppm NO markedly and significantly decreased MI size and improved LV function after ischemia and reperfusion in mice. NO inhalation may represent a novel method to salvage myocardium at risk of I/R injury.

In a murine model of DOX-induced cardiac injury, TDI detects LV dysfunction prior to alterations in conventional echocardiographic indices and predicts mortality. This study suggests that TDI may be a reliable tool to detect early subtle changes in DOX-induced cardiac dysfunction.

Abstract-Myocardial dysfunction contributes to the high mortality of patients with endotoxemia. Although nitric oxide (NO) has been implicated in the pathogenesis of septic cardiovascular dysfunction, the role of myocardial NO synthase 3 (NOS3) remains incompletely defined. Here we show that mice with cardiomyocyte-specific NOS3 overexpression (NOS3TG) are protected from myocardial dysfunction and death associated with endotoxemia. Endotoxin induced more marked impairment of Ca 2ϩ transients and cellular contraction in wild-type than in NOS3TG cardiomyocytes, in part, because of greater total sarcoplasmic reticulum Ca 2ϩ load and myofilament sensitivity to Ca 2ϩ in the latter during endotoxemia. Endotoxin increased reactive oxygen species production in wild-type but not NOS3TG hearts, in part, because of increased xanthine oxidase activity. Inhibition of NOS by N G -nitro-L-arginine-methyl ester restored the ability of endotoxin to increase reactive oxygen species production and xanthine oxidase activity in NOS3TG hearts to the levels measured in endotoxin-challenged wild-type hearts. Allopurinol, a xanthine oxidase inhibitor, attenuated endotoxin-induced reactive oxygen species accumulation and myocardial dysfunction in wild-type mice. The protective effects of cardiomyocyte NOS3 on myocardial function and survival were further confirmed in a murine model of polymicrobial sepsis. These results suggest that increased myocardial NO levels attenuate endotoxin-induced reactive oxygen species production and increase total sarcoplasmic reticulum Ca 2ϩ load and myofilament sensitivity to Ca 2ϩ , thereby reducing myocardial dysfunction and mortality in murine models of septic shock. Key Words: nitric oxide Ⅲ endotoxin Ⅲ reactive oxygen species Ⅲ calcium handling Ⅲ myofilament S eptic shock is a complex syndrome that claims more than 200 000 lives per year in the United States. 1 Endotoxemia occurs frequently in septic shock, and severe manifestations of this syndrome include cardiac depression. 2 Although cytokines and nitric oxide (NO) have been implicated in the pathogenesis of septic shock, the underlying mechanisms of myocardial depression of sepsis remains incompletely understood.High levels of NO produced by NO synthase 2 (NOS2) contribute to the systemic hypotension and myocardial dysfunction associated with sepsis. 3 However, despite the prominent role of NOS2 in cardiovascular dysfunction of sepsis, clinical trials using NOS inhibitors that are not isoform specific have been associated with increased mortality in septic patients, presumably caused by further impairment of cardiac function. 4 Although these observations indirectly suggest that NOS1 and/or NOS3 may have beneficial effects on myocardial function in sepsis, other studies using NOS isoform-deficient mice reported variable results. For instance, NOS3-deficient mice (NOS3 Ϫ/Ϫ ) were reported to have higher mortality at 1 day after endotoxin challenge compared with wild-type (WT) mice. 5 In contrast, another study showed that endotoxin-induced hypoten...

Background-Flavoprotein reductases are involved in the generation of reactive oxygen species by doxorubicin. The objective of the present study was to determine whether or not one flavoprotein reductase, endothelial nitric oxide synthase (nitric oxide synthase 3 [NOS3]), contributes to the cardiac dysfunction and injury seen after the administration of doxorubicin. Methods and Results-A single dose of doxorubicin (20 mg/kg) was administered to wild-type (WT) mice, NOS3-deficient mice (NOS3 Ϫ/Ϫ ), and mice with cardiomyocyte-specific overexpression of NOS3 (NOS3-TG). Cardiac function was assessed after 5 days with the use of echocardiography. Doxorubicin decreased left ventricular fractional shortening from 57Ϯ2% to 47Ϯ1% (PϽ0.001) in WT mice. Compared with WT mice, fractional shortening was greater in NOS3Ϫ/Ϫ and less in NOS3-TG after doxorubicin (55Ϯ1% and 35Ϯ2%; PϽ0.001 for both). Cardiac tissue was harvested from additional mice at 24 hours after doxorubicin administration for measurement of cell death and reactive oxygen species production. Doxorubicin induced cardiac cell death and reactive oxygen species production in WT mice, effects that were attenuated in NOS3 Ϫ/Ϫ and were more marked in NOS3-TG mice. Finally, WT and NOS3 Ϫ/Ϫ mice were treated with a lower dose of doxorubicin (4 mg/kg) administered weekly over 5 weeks. Sixteen weeks after beginning doxorubicin treatment, fractional shortening was greater in NOS3 Ϫ/Ϫ than in WT mice (45Ϯ2% versus 28Ϯ1%; PϽ0.001), and mortality was reduced (7% versus 60%; PϽ0.001). Conclusions-These

Introduction Sudden cardiac arrest (CA) is a leading cause of death worldwide. Breathing nitric oxide (NO) reduces ischemia-reperfusion (IR) injury in animal models and in patients. The objective of this study was to learn whether inhaled NO improves outcomes after CA and cardiopulmonary resuscitation (CPR). Methods and Results Adult male mice were subjected to potassium-induced CA for 7.5 min whereupon CPR was performed with chest compression and mechanical ventilation. One hour after CPR, mice were extubated and breathed air alone or air supplemented with 40 parts per million (ppm) NO for 23h. Mice that were subjected to CA/CPR and breathed air exhibited a poor 10-day survival rate (4/13), depressed neurological and left ventricular (LV) function, and increased caspase-3 activation and inflammatory cytokine induction in the brain. Magnetic resonance imaging revealed brain regions with marked water diffusion abnormality 24h after CA/CPR in mice that breathed air. Breathing air supplemented with NO for 23h starting 1h after CPR attenuated neurological and LV dysfunction 4 days after CA/CPR and markedly improved 10-day survival rate (11/13, P=0.003 vs Air). The protective effects of inhaled NO on the outcome after CA/CPR were associated with reduced water diffusion abnormality, caspase-3 activation, and cytokine induction in the brain and increased serum NOx levels. Deficiency of the α1 subunit of soluble guanylate cyclase (sGC), a primary target of NO, abrogated the ability of inhaled NO to improve outcomes after CA/CPR. Conclusions These results suggest that NO inhalation after CA and successful CPR improves outcome via sGC-dependent mechanisms.

MyD88 is an adaptor protein critical for innate immune response against microbial infection and in certain noninfectious tissue injury. The present study examined the role of MyD88 in myocardial inflammation and injury after ischemia-reperfusion (I/R). I/R was produced by coronary artery ligation for 30 min followed by reperfusion. The ratios of area at risk to left ventricle (LV) were similar between wild-type (WT) and MyD88-deficient (MyD88-/-) mice. However, 24 h after I/R, the ratios of myocardial infarction to area at risk were 58% less in MyD88(-/-) than in WT mice (14 +/- 2% vs. 33 +/- 6%, P = 0.01). Serial echocardiographic studies demonstrated that there was no difference in baseline LV contractile function between the two groups. Twenty-four hours after I/R, LV ejection fraction (EF) and fractional shortening (FS) in WT mice were reduced by 44% and 62% (EF, 51 +/- 2%, and FS, 22 +/- 1%, P < 0.001), respectively, and remained depressed on the seventh day after I/R. In comparison, EF and FS in MyD88(-/-) mice were 67 +/- 3% and 33 +/- 2%, respectively, after I/R (P < 0.001 vs. WT). Similarly, LV function, as demonstrated by invasive hemodynamic measurements, was better preserved in MyD88(-/-) compared with WT mice after I/R. Furthermore, when compared with WT mice, MyD88(-/-) mice subjected to I/R had a marked decrease in myocardial inflammation as demonstrated by attenuated neutrophil recruitment and decreased expression of the proinflammatory mediators keratinocyte chemoattractant, monocyte chemoattractant protein-1, and ICAM-1. Taken together, these data suggest that MyD88 modulates myocardial inflammatory injury and contributes to myocardial infarction and LV dysfunction during I/R.