Constitutive nitric oxide production by rat alveolar macrophages
Miles, P.R.; Bowman, L.; Rengasamy, A.; Huffman, L.
American Journal of Physiology 274(3): L360-L368
1998
ISSN/ISBN: 0002-9513 PMID: 9530171 Document Number: 486477
Results from previous studies suggest that alveolar macrophages must be exposed to inflammatory stimuli to produce nitric oxide (cntdotNO). In this study, we report that naive unstimulated rat alveolar macrophages do produce cntdotNO and attempt to characterize this process. Western blot analysis demonstrates that the enzyme responsible is an endothelial nitric oxide synthase (eNOS). No brain or inducible NOS can be detected. The rate of cntdotNO production is apprx 0.07 nmol cntdot 106 cells-1 cntdot h-1, an amount that is less than that produced by the eNOS found in alveolar type II or endothelial cells. Alveolar macrophage cntdotNO formation is increased in the presence of extracellular L-arginine, incubation medium containing magnesium and no calcium, a calcium ionophore (A-23187), or methacholine. cntdotNO production is inhibited by NG-nitro-L-arginine methyl ester (L-NAME) but not by NG-nitro-L-arginine, L-N5-(1-iminomethyl)ornithine hydrochloride, or aminoguanidine. Incubation with ATP, ADP, or histamine also inhibits cntdotNO formation. Some of these properties are similar to and some are different from properties of eNOS in other cell types. Cellular cntdotNO levels do not appear to be related to ATP or lactate content. Alveolar macrophage production of cntdotNO can be increased approximately threefold in the presence of lung surfactant or its major component, dipalmitoyl phosphatidylcholine (DPPC). The DPPC-induced increase in -NO formation is time and concentration dependent, can be completely inhibited by L-NAME, and does not appear to be related to the degradation of DPPC by alveolar macrophages. These results demonstrate that unstimulated alveolar macrophages produce cntdotNO via an eNOS and that lung surfactant increases cntdotNO formation. This latter effect may be important in maintaining an anti-inflammatory state in vivo.