Background: Ethanol (ETOH) inhibits Escherichia coli endotoxin [lipopolysaccharide (LPS)]-mediated induction of nitric oxide (NO) synthase (NOS) transcription and translation in macrophages and neutrophils [polymorphonuclear (PMN) cells] within the lung. ETOH also inhibits PMN recruitment into the lung and enhances NOS I-mediated production of NO. The contribution of the individual NOS isozymes to ETOH-mediated suppression of the host defense response to lung infection has not been defined.
Methods: We evaluated the role of constitutive NOS I and NOS II in ETOH-mediated inhibition of PMN recruitment into the lung and ETOH-mediated suppression of lung clearance of inhaled Klebsiella pneumonia (K. pneumoniae) in female, homozygous transgenic mice deficient in the genes for NOS I (nNOS-KO) or NOS II (iNOS-KO) and their wild-type controls (WT).
Results: Four hours after intratracheal administration of LPS or aerosol inhalation of K. pneumoniae, the lung content of PMNs obtained by bronchoalveolar lavage from WT mice was significantly reduced when compared with that obtained from the lungs of nNOS-KO and iNOS-KO mice. Pretreatment of WT mice with the NOS II inhibitor L-N6-iminoethyllysine (L-NIL; 10 mg/kg, i.p.) or with the NOS I inhibitor 7-nitroindazole (7-NI) (10, 25, or 40 mg/kg, i.p.) 30 min before LPS administration enhanced the lung content of PMNs recoverable by bronchoalveolar lavage. However, pretreatment of iNOS-KO with L-NIL did not affect lung recruitment of PMNs. Moreover, administration of 25 or 40 mg/kg, i.p. of 7-NI to nNOS-KO mice resulted in death of all the animals within 10 min. Pretreatment of nNOS-KO with 7-NI (10 mg/kg) did not affect LPS-stimulated PMN recruitment. Pretreatment of mice with ETOH (4.5 g/kg, i.p.) produced a greater inhibition of LPS-stimulated lung recruitment of PMNs in iNOS-KO mice than in WT mice. In contrast, pretreatment of nNOS-KO with ETOH produced little inhibition of LPS-stimulated lung recruitment of PMNs when compared with that measured in WT mice. Finally, 4 hr after aerosol inhalation of K. pneumoniae, lung clearance of this bacteria was enhanced in iNOS-KO when compared with WT and inhibited in nNOS-KO when compared with WT mice. ETOH-mediated suppression of lung clearance of K. pneumoniae was unaffected in nNOS-KO mice and enhanced in the iNOS-KO mice, when compared with that obtained in WT mice. ETOH-stimulated the production of NOS I-derived nitrate and nitrite production by rat brain and lung and inhibited LPS-induced NOS II mRNA, protein, and production of nitrate and nitrite anion. Finally, inhibition of NOS I and NOS I deletion inhibited the in vivo metabolism of ETOH.
Conclusions: We conclude that constitutive NOS I is involved in protection of the lung from stressor-induced lung injury. NOS I within the PMNs may limit PMN recruitment into the lung. Speculatively, NOS II-derived NO may also limit PMN-induced lung damage at the expense of a slower clearance of the bacterial burden.