SPECIES-DIFFERENCES IN NO FORMATION BY RAT AND HAMSTER ALVEOLAR MACROPHAGES IN-VITRO

Nitric oxide (NO) is a cellular mediator and regulator of multiple bio logic functions. NO released by alveolar macrophages (AM) is suggested to play a role in mediating pulmonary injury. In murine and rat macro phages, the expression of inducible NO synthase (iNOS) and the release of NO are well established. However, the existence of such a pathway in other species remains controversial. In this study, we examined NO production and iNOS expression by AM from rats and hamsters, two labor atory animal species that are characterized by their disparate pulmona ry responses to various inhaled irritants/toxicants. AM were treated w ith lipopolysaccharide (LPS), interferon-gamma (IFN-gamma), or tumor n ecrosis factor-alpha (TNF-(alpha)) in vitro, and nitrite, the stable o xidation product of NO, was assayed by the Griess reaction. Rat AM pro duced NO in a dose- and time-dependent manner upon stimulation with LP S and/or IFN-gamma, but not with TNF-alpha. Surprisingly, hamster AM d id not release detectable levels of NO after the same treatment. Altho ugh iNOS expression was demonstrated in rat AM by immunocytochemical a nd Western blot analyses, no induction of iNOS expression could be fou nd in hamster AM. Using reverse transcriptase-polymerase chain reactio n (RT-PCR) analysis, we found that rat and hamster AM could be induced to express iNOS mRNA after treatment with LPS and IFN-gamma. The resu lts presented here indicate that hamster AM, in contrast to rat AM, la ck the ability to express iNOS protein and to generate NO in response to LPS, IFN-gamma, or TNP-alpha in vitro. In conclusion, our data sugg est striking differences in iNOS regulation and NO production by AM fr om rats and hamsters, two rodent species that are commonly used in bio medical research and well-known for their disparate responses to pulmo nary irritants/toxicants.