Response of the septic vasculature to prolonged vasopressor therapy with N (omega-monomethyl-L-arginine) and epinephrine in canines

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Abstract
To investigate the effect of blocking nitric oxide production on cardiovascular function and survival in canine septic shock treated with or without a conventional vasopressor. Randomized, controlled trial. An animal research laboratory at the National Institutes of Health. Sixty purpose-bred beagles. Fibrin clots containing Escherichia coli were surgically placed into the peritoneal cavity. Nomega-monomethyl-L-arginine (L-NMMA) 10 mg/kg followed by 0.5, 1.0, or 4.0 mg/kg/hr), epinephrine (1 [micro sign]g/kg/min), both, or neither were infused for 24 hrs beginning 6 hrs after the onset of infection. All animals received fluid and antibiotic therapy. Serum nitric oxide metabolites, nitrite and nitrate, increased with infection (p = .024) and decreased with L-NMMA (p = .004, all doses combined). Myocardial nitric oxide synthase activity was ranked as follows: nonsurvivors > survivors > noninfected controls (p .4), perhaps because L-NMMA increased pulmonary artery occlusion pressure (p = .02). From 9 to 24 hrs, epinephrine, in the absence or presence of L-NMMA, blunted recovery of cardiac index (p or=to.69). The tested doses showed that nitric oxide production was inhibited by L-NMMA in canine septic shock, but mortality and myocardial depression were unaffected. These results suggest that if L-NMMA has a beneficial effect on survival rates in septic shock, it is small. (Crit Care Med 1998; 26:877-886)