Modulation of citric acid-induced cough following lipopolysaccharide-mediated neutrophilia in the guinea pig

This investigation examined a possible correlation between lipopolysaccharide (LPS)-induced pulmonary neutrophilia and cough. Conscious male guinea pigs were acutely exposed to aerosolized LPS and thereafter at various times challenged with citric acid aerosol (CA; 250 mM) to induce cough followed by bronchoalveolar lavage (BAL) to quantitate inflammatory cell accumulation. LPS caused a hyporesponsive cough at 24 h post-LPS with neutrophilia apparent from 2 h post-LPS. By 96 h post-LPS both cough and neutrophilia had returned towards normal. Dexamethasone (DEX, 2 mgkg−1/day for 3 days prior) did not affect the cough hyporesponsiveness at 24 h; however it attenuated LPS-induced BAL fluid neutrophilia. Since LPS can stimulate inducible nitric oxide synthase (iNOS) we hypothesized that the cough hyporesponsiveness may involve nitric oxide. To investigate this we treated animals with an aerosolized iNOS inhibitor 1400W (1 mM) immediately prior to LPS. 1400W had no significant effect on either cough hyporesponsiveness or BAL fluid neutrophilia at 24 h post-LPS. Despite differing effects on neutrophilia, these findings clearly indicate that neither DEX nor iNOS inhibition had any direct effect on LPS-induced cough hyporesponsiveness. The mechanism underlying the LPS-induced cough hyporesponsiveness does not appear to be directly linked to LPS-induced neutrophilic inflammation.