Prolonged in vivo hypoxia enhances nitric oxide synthase type I and type III gene expression in adult rat lung.

Abstract

Prolonged hypoxia in the adult rat causes a decline in endothelium-derived nitric oxide (NO) production in the pulmonary circulation. To evaluate whether this is related to a decrease in endothelial NO synthase (NOS-III) expression, we determined the effects of hypobaric hypoxia (7 or 21 days) on NOS-III gene expression in adult rat lung. Neuronal NOS (NOS-I) expression was also examined; NOS-I has been immunohistochemically localized to rat bronchiolar epithelium. NOS-III and NOS-I mRNA abundance were assessed in reverse transcription-polymerase chain reaction assays and the proteins were evaluated by immunoblot analysis. After 7 and 21 days of hypoxia, there were increases in the steady-state levels of both NOS-III and NOS-I mRNA, rising 2.7- to 3.0-fold and 2.5- to 2.8-fold, respectively. These findings were confirmed by Northern analyses. In parallel, NOS-III and NOS-I protein abundance were also increased with hypoxia by 3.0- to 3.5-fold and 2.4- to 3.0-fold, respectively. NOS activity detected by [3H]arginine to [3H]citrulline conversion rose 109%. Thus, prolonged in vivo hypoxia causes enhancement of NOS-III and NOS-I gene expression in adult rat lung, indicating that the pulmonary expression of these genes is modulated in vivo. The increase in NOS-III expression does not explain the declines in pulmonary endothelial NO production previously observed following prolonged hypoxia in this model. Alternatively, the fall in NO production may be related to diminished NOS co-factor availability.

Pulmonary PKG-1 is upregulated following chronic hypoxia

“…Previous studies from our laboratory (32-34) and others (18,26,28,36,37) suggest that CH augments EDNO-dependent pulmonary vasodilation, a response associated with upregulation of pulmonary eNOS mRNA and protein levels (18,21,26,33,34,39,46), as well as increased synthesis of NO (18,26,44). However, despite this enhanced reactivity to EDNO-mediated agonists, we have recently reported that CH attenuates pulmonary vasodilatory responsiveness to both exogenous NO (19) and to the membrane-permeable cGMP analog 8-BrcGMP (19).…”

“…isolated rat lung; nitric oxide; pulmonary hypertension; 8-bromoguanosine 3',5'-cyclic monophosphate; KT-5823; Rp-␤-phenyl-1, N2-etheno-8-bromoguanosine 3',5'-cyclic monophosphorothioate CHRONIC EXPOSURE TO HYPOXIA has been shown to augment pulmonary vasodilatory responses to endothelium-derived nitric oxide (EDNO)-dependent vasodilators (18, 26, 28, 32-34, 36, 37). EDNO is synthesized in the vasculature by endothelial nitric oxide synthase (eNOS), and several studies have demonstrated that chronic hypoxia (CH) is associated with increased pulmonary eNOS levels, gene expression, and activity (18,21,26,33,34,39,46). Consistent with elevated eNOS levels, nitric oxide (NO) synthesis appears to be greater in lungs isolated from CH rats compared with controls (18,26,44).…”

Flow-mediated dilatation of the brachial artery in pregnancy at high altitude

“…In vitro and animal studies have demonstrated that in situations of acute hypoxia NO synthesis may be upregulated 16,17 or downregulated 18 . Similarly, animal studies in situations of chronic hypoxia have demonstrated that NO synthase in the lungs 19 or in the brain 20 may be upregulated while production of NO by endothelial cells is suppressed 20,21 . Animal studies at high altitude have also given conflicting results regarding NO activity.…”

Response of nitric oxide pathway to l-arginine infusion at the altitude of 4,350 m

“…In patients with pulmonary hypertension, Arg reduced the pulmonary vascular resistance and the magnitude of the pulmonary vasodilatory response was correlated to the level of L-cit [11]. Furthermore, although NOS expression was upregulated in the early course of development of HPV [25], NOS activity was not increased if the substrate for the NOS enzyme was limiting [26,27]. Thus, the increase in L-cit and the short-term oxygenation effect of exogenous Arg at high altitude may be due to enhanced NO production in the pulmonary vasculature, and increase in Arg availability can promote L-cit/NO synthesis in high altitude.…”