Regulation of murine airway responsiveness by endothelial nitric oxide synthase

Abstract

Nitric oxide (NO) is a potent vasodilator, but it can also modulate contractile responses of the airway smooth muscle. Whether or not endothelial (e) NO synthase (NOS) contributes to the regulation of bronchial tone is unknown at present. Experiments were designed to investigate the isoforms of NOS that are expressed in murine airways and to determine whether or not the endogenous release of NO modulates bronchial tone in wild-type mice and in mice with targeted deletion of eNOS [eNOS(-/-)]. The presence of neuronal NOS (nNOS), inducible NOS (iNOS), and eNOS in murine trachea and lung parenchyma was assessed by RT-PCR, immunoblotting, and immunohistochemistry. Airway resistance was measured in conscious unrestrained mice by means of a whole body plethysmography chamber. The three isoforms of NOS were constitutively present in lungs of wild-type mice, whereas only iNOS and nNOS were present in eNOS(-/-) mice. Labeling of nNOS was localized in submucosal airway nerves but was not consistently detected, and iNOS immunoreactivity was observed in tracheal and bronchiolar epithelial cells, whereas eNOS was expressed in endothelial cells. In wild-type mice, treatment with N-nitro-L-arginine methyl ester, but not with aminoguanidine, potentiated the increase in airway resistance produced by inhalation of methacholine. eNOS(-/-) mice were hyperresponsive to inhaled methacholine and markedly less sensitive to N-nitro-L-arginine methyl ester. These results demonstrate that the three NOS isoforms are expressed constitutively in murine lung and that NO derived from eNOS plays a physiological role in controlling bronchial airway reactivity.

Enhanced nitric oxide production associated with airway hyporesponsiveness in the absence of IL-10

“…In this case, elevated levels of NO in the lung in the absence of IL-10 could result in NO-induced vasodilation and enhanced washout that would manifest as airway hyporesponsiveness in the face of a cholinergic challenge, as we observed. This explanation would be consistent with findings that eNOS is a major source of airway NO and is strongly associated with AR in mice (11). Further study is necessary to determine whether this mechanism may be a reason for these observations in this and other models of AR.…”

“…The current results displayed a stronger reduction of E NO with L-NIL compared with L-NAME, which suggests that L-NIL was more effective in suppressing airway NO production, perhaps by iNOS, at the dose level that we used. However, in the absence of an applied experimental stimulus such as airway inflammation, it is also possible that the constitutive/neuronal form, nNOS or NOS I, may dominate (9); furthermore some reports suggest that AR in mice may be linked to the endothelial isoform, eNOS or NOS III (11). These findings indicate that further studies are necessary to determine the relative effective doses of NOS isoform-specific inhibitors in the absence of IL-10, when regulation of NOS may be altered.…”

Lung ischemia-reperfusion injury: a molecular and clinical view on a complex pathophysiological process

“…eNOS is located in the proximal bronchiolar epithelium (184) and in the endothelial layer of bronchial and large pulmonary blood vessels (63).…”

Ablation of Arg1 in hematopoietic cells improves respiratory function of lung parenchyma, but not that of larger airways or inflammation in asthmatic mice

“…Both Nos1-and Nos3-deficient mice suffer from a more pronounced AHR than wild-type mice (17,18), whereas in Nos3-overexpressing mice, allergen-induced AHR to methacholine is completely abolished (11,51), indicating a prime role for NO in airway relaxation. In agreement, inhibition of arginase activity in OVA/OVA-treated Nos2 Ϫ/Ϫ mice did not induce AHR, suggesting that NOS1 and -3 used the increased tissue arginine levels to produce more NO and relax the smooth muscles of the larger airways (42).…”