Potential role of nitric oxide in the pathophysiology of experimental bacterial meningitis in rats

We have investigated the possible role of nitric oxide (NO) in the pathophysiology of bacterial meningitis (BM) by using the rat model of experimental BM. The nitrite concentration in cerebrospinal fluid (CSF) was used as a measure of NO production in vivo since NO rapidly degrades to nitrite and nitrate. Rats were inoculated intracisternally with live bacteria (5 x 10(6) CFU of Haemophilus influenzae type b strain DL42 or Rd-/b+/O2), with bacterial endotoxin (20 ng of DL42 lipooligosaccharide [LOS] or 200 ng of Escherichia coli lipopolysaccharide), or with a saline control vehicle. CSF samples were collected preinoculation and at the time of maximal alteration in blood-brain barrier permeability (BBBP). CSF [nitrite] was quantified by measuring A550 after addition of the Greiss reagent and comparison to a standard curve of sodium nitrite. Rats inoculated with either DL42, Rd-/b+/O2, LOS, or lipopolysaccharide demonstrated a significantly elevated mean peak CSF [nitrite] (8.34, 15.62, 10.75, and 10.44 mM, respectively) versus the concentration prior to treatment and/or those in saline-treated animals (5.29 and 5.33 mM, respectively; P < 0.05 for each comparison). We then determined if there was a correlation between CSF [nitrite] and percent BBBP (%BBBP) at various time points postinoculation with Rd-/b+/O2. %BBBP was defined as the concentration of systemically administered 125I-labeled bovine serum albumin in the CSF divided by the level of 125I-labeled bovine serum albumin in serum multiplied by 100. The mean %BBBP increased in tandem with the mean CSF [nitrite] (R = 0.84, P = 0.018), which peaked at 18 h in the absence of a change in the serum [nitrite]. Systemic administration of the NO synthase inhibitor N-nitro-L-arginine methyl ester demonstrated a significant reduction of mean CSF nitrite production (0.95 versus 6.0 mM in controls; P = 0.02) when administered intravenously to animals which had been inoculated intracisternally with 20 ng of LOS. Suppression of mean leukocyte pleocytosis (3,117 versus 11,590 leukocytes per mm3 in control LOS-challenged rats; P = 0.03) and mean alterations of BBBP (2.11 versus 6.49% in control LOS-challenged rats; P = 0.009) was observed concomitantly with decreased CSF [nitrite]. These results support the hypothesis that NO contributes to increased %BBBP in experimental BM.