Neuronal NOS-inhibition in the setting of septic cardiomyopathy

Introduction

Nitric oxide (NO) plays a central role in the pathogenesis of sepsis. Recently, we demonstrated that endothelial NOS (eNOS) contributes to endogenous NO-production and modulates inflammation, associated with preserved cardiac function resulting in prolonged survival of eNOS^-/- compared with wild-type (WT) mice. The role of neuronal NOS (nNOS) in septic cardiomyopathy remains unclear. This study's aim is to elucidate the influence of nNOS in the presence/absence of eNOS on cardiac function and survival in a clinically relevant model of sepsis.

Methods

Inhibition of nNOS was achieved via continuous application of the selective nNOS-inhibitor Vinyl-L-NIO (VL-NIO) (0.02 mg/kg BW/hour) using an osmotic mini pump. B6/c57 WT and eNOS^-/- mice were rendered septic by cecum ligation and puncture (CLP). After 12 hours heart function was analyzed using a pressure-volume catheter placed in the left ventricle. For catecholamine responsiveness, norepinephrine was applied (0.4 μg/kg BW/minute, intraperitoneally). NOx-levels in plasma were measured using high-pressure performing liquid chromatography.

Results

Inhibition of nNOS via VL-NIO application resulted in significantly reduced nitrate plasma levels and prolonged survival (WT CLP + VL-NIO = 38 hours vs WT CLP = 29 hours). However, cardiac function and norepinephrine responsiveness were not improved compared with untreated septic WT. In contrast to WT, application of VL-NIO in eNOS^-/- had no influence on plasma nitrate levels, while cardiac function and survival were significantly impaired compared with untreated septic eNOS^-/-. Impaired cardiac function was accompanied by decreased survival time (eNOS^-/- CLP + VL-NIO = 29.5 hours vs eNOS^-/- CLP = 69.5 hours).

Conclusions

Pharmacologic inhibition of nNOS result in significant reduction of plasma nitrate levels and prolonged survival compared with untreated septic WT despite unimproved septic cardiomyopathy. In contrast, the significant survival benefit of septic eNOS^-/- compared with septic WT was abrogated by pharmacologic nNOS inhibition. Furthermore, the latter developed severe septic cardiomyopathy. Whether eNOS acts as modulator of nNOS in this setting remains to be clarified by further studies.