Effect of inhibition of NO synthase on vascular reactivity in a rat model of hyperdynamic sepsis

To evaluate the role of nitric oxide (NO) in the attenuated vascular reactivity observed in sepsis, we utilized the specific NO synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME). Male Sprague-Dawley rats (n = 16) were randomized to either sepsis induced by cecal ligation and perforation (CLP; n = 8) or sham procedure (Sham; n = 8). Vascular reactivity was assessed by measuring the pulmonary pressor response to hypoxia (HPV) (fractional inspired O2 concentration = 0.08) and the pulmonary and systemic pressor response to an intravenous infusion of phenylephrine (1.5-6.0 micrograms.kg-1.min-1). Twenty-four hours after surgery, CLP animals had significantly attenuated HPV compared with Sham animals. In response to hypoxia the change in total pulmonary vascular resistance during hypoxia was 0.008 +/- 0.004 and 0.021 +/- 0.006 mmHg.min-ml-1 in CLP and Sham animals, respectively (P < 0.05). The pulmonary and systemic blood pressure response to phenylephrine was also attenuated in CLP compared with Sham animals. After L-NAME infusion (15 mg/kg), there was a significant augmentation of the HPV response in Sham animals. In contrast, the HPV response in CLP animals was unchanged after L-NAME. The attenuated pressor response to phenylephrine in neither the pulmonary nor the systemic circulation was changed after the administration of L-NAME. These data suggest that in rats, excess NO is not an important mediator of the attenuated vascular reactivity observed in sepsis.