Effects of nitric oxide synthase inhibition combined with nitric oxide inhalation in a porcine model of endotoxin shock.

1. The present investigation compares the effects of intravenous infusion of the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA) with that of an inhalation with NO gas in a porcine model of endotoxin (lipopolysaccharide, LPS) shock. In addition, the effects of the combination of these two treatments were also investigated. 2. Male pigs were anaesthetized and instrumented for the measurement of haemodynamic parameters. Blood samples were withdrawn at different time intervals for determination of blood gases, pH, and plasma levels of nitrite/nitrate and tumour necrosis factor. 3. Endotoxin infusion (15 micrograms kg-1 h-1 for 3 h) caused a progressive fall in mean arterial blood pressure (MABP) and cardiac output (CO) and a biphasic increase in mean pulmonary arterial pressure (MPAP) and pulmonary vascular resistance (PVR). A continuous infusion of L-NMMA (0.1 mg kg-1 min-1) significantly attenuated the fall in MABP, but did not affect MPAP, CO and PVR. NO-inhalation (50 p.p.m.) did not affect MABP, but significantly blunted the biphasic increase in MPAP and PVR and significantly delayed the fall in CO. The combination of L-NMMA infusion (0.1 mg kg-1 min-1) with NO-inhalation (50 p.p.m.) completely prevented the fall in MABP, significantly improved CO, and attenuated the biphasic increase in MPAP and PVR. 4. Endotoxin also caused a decline in PaO2 and a rise of PaCO2. Infusion of L-NMMA neither affected the fall in PaO2 nor the increase in PaCO2. In contrast, inhalation with NO gas alone as well as the combined administration of L-NMMA infusion and NO-inhalation completely prevented the fall in Pao2 and significantly protected against the increase in Paco2.5. Infusion of endotoxin for 180 min resulted in a mortality of 58%, which was not affected by L-NMMA (63%). In contrast, treatment of LPS-animals with either NO-inhalation alone or NO inhalation plus L-NMMA completely prevented mortality.6. This investigation demonstrates that treatment with NO-inhalation, in order to prevent the dramatic increase in MPAP, PVR and the alterations in peripheral blood gases combined with systemic L-NMMAto improve systemic MABP and thus organ perfusion, may be a new therapeutic regimen in the treatment of septic shock.