Role of myocardial neuronal nitric oxide synthase-derived nitric oxide in β-adrenergic hyporesponsiveness after myocardial infarction-induced heart failure in rat

Background - An emerging concept is that a neuronal isoform of nitric oxide synthase (NOS1) may regulate myocardial contractility. However, a role for NOS1-derived nitric oxide (NO) in heart failure (HF) has not been defined. Methods and Results - Using a model of myocardial infarction-induced HF, we demonstrated that cardiac NOS1 expression and activity increased in HF rats (P < 0.05 and P <0.001 versus shams, respectively). This was associated with translocation of NOS1 from the ryanodine receptor to the sarcolemma through interactions with caveolin-3 in HF hearts. With ex vivo and in vivo pressure-volume analysis, cardiac NOS1-derived NO was found to be negatively inotropic in shams but not HF hearts. Ventricular elastance (E-es) was significantly reduced in HF rats (P < 0.05), and tau, the time constant of left ventricular relaxation, was prolonged ( both P < 0.05). Acute NOS1 inhibition significantly increased E-es by 33 +/- 3% and tau by 17 +/- 2% ( P < 0.05) in shams, although these effects were significantly attenuated in HF hearts. beta-Adrenergic stimulation induced a marked increase in systolic performance in sham hearts, with the responses being significantly blunted in HF hearts. Ees increased by 163 +/- 42% ( P < 0.01) in sham hearts and 56 +/- 9% in HF hearts, and LV + dP/dt increased by 97 +/- 9% ( P < 0.01) in shams and 37 +/- 7% ( P < 0.05) in the HF group. Interestingly, preferential NOS1 inhibition enhanced the blunted responses of LV + dP/dt and E-es to beta-adrenergic stimulation in HF rats but had no effect in shams. Conclusions - These results provide the first evidence that increased NOS1-derived NO production may play a role in the autocrine regulation of myocardial contractility in HF.