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...

Nitric oxide (NO) has been implicated in the pathogenesis of septic shock. However, the role of NO synthase 3 (NOS3) during sepsis remains incompletely understood. Here, we examined impact of NOS3 deficiency on systemic inflammation and myocardial dysfunction during peritonitis-induced polymicrobial sepsis. Severe polymicrobial sepsis was induced by colon ascendens stent peritonitis (CASP) in wild-type (WT) and NOS3-deficient (NOS3KO) mice. NOS3KO mice exhibited shorter survival time than did WT mice after CASP. NOS3 deficiency worsened systemic inflammation assessed by the expression of inflammatory cytokines in the lung, liver, and heart. CASP markedly increased the number of leukocyte infiltrating the liver and heart in NOS3KO but not in WT mice. The exaggerated systemic inflammation in septic NOS3KO mice was associated with more marked myocardial dysfunction than in WT mice 22h after CASP. The detrimental effects of NOS3-deficiency on myocardial function after CASP appear to be caused by impaired Ca2+ handling of cardiomyocytes. The impaired Ca2+ handling of cardiomyocytes isolated from NOS3KO mice subjected to CASP was associated with depressed mitochondrial ATP production, a determinant of the Ca2+ cycling capacity of sarcoplasmic reticulum (SR) Ca2+-ATPase. The NOS3-deficiency-induced impairment of the ability of mitochondria to produce ATP after CASP was at least in part attributable to reduction in mitochondrial respiratory chain complex I activity. These observations suggest that NOS3 protects against systemic inflammation and myocardial dysfunction after peritonitis-induced polymicrobial sepsis in mice.