Maintained upregulation of pulmonary eNOS gene and protein expression during recovery from chronic hypoxia

Abstract

We previously demonstrated augmented endothelium-derived nitric oxide (EDNO)-dependent pulmonary arterial dilation and increased arterial endothelial nitric oxide synthase (eNOS) levels in chronic hypoxic (CH) and monocrotaline (nonhypoxic) models of pulmonary arterial hypertension. Therefore, we hypothesized that the long-term elevation of arterial eNOS levels associated with CH is related to pulmonary hypertension or some factor(s) associated with hypertension and not directly to hypoxia. To test this hypothesis, we examined responses to the EDNO-dependent dilator ionomycin in U-46619-constricted, isolated, saline-perfused lungs from control rats, CH (4 wk at 380 mmHg) rats, and rats previously exposed to CH but returned to normoxia for 4 days or 2 wk. Microvascular pressure was assessed by double-occlusion technique, allowing calculation of segmental resistances. In addition, vascular eNOS immunoreactivity was assessed by quantitative immunohistochemistry, and eNOS mRNA abundance was determined by RT-PCR assays. Our findings indicate that 4-day and 2-wk posthypoxic rats exhibit persistent pulmonary hypertension, likely due to maintained arterial remodeling and polycythemia associated with prior exposure to CH. Furthermore, arterial dilation to ionomycin was augmented in lungs from each experimental group compared with controls. Finally, arterial eNOS immunoreactivity and whole lung eNOS mRNA levels remained elevated in posthypoxic animals. These findings suggest that altered vascular mechanical forces or vascular remodeling contributes to enhanced EDNO-dependent arterial dilation and upregulation of arterial eNOS in various models of established pulmonary hypertension.

Pulmonary PKG-1 is upregulated following chronic hypoxia

“…Right ventricular (RV) hypertrophy was assessed as an index of CH-induced pulmonary hypertension, as previously described (19,33,34). In brief, after isolation of the heart, the atria and major vessels were removed from the ventricles.…”

“…Rats from each group were anesthetized with pentobarbital sodium (52 mg ip), and the lungs were isolated for recirculating perfusion with a physiological saline solution (PSS) as previously described (19,33,34). After the trachea was cannulated with a 17-gauge needle stub, the lungs were ventilated with a Harvard positive-pressure rodent ventilator (model 683) at a frequency of 55 breaths/min and a tidal volume of 2.5 ml with a warmed and humidified gas mixture (6% CO 2 in room air).…”

“…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).…”

Discrepant distribution of big endothelin (ET)-1 and ET receptors in the pulmonary artery

“…These findings suggest that up-regulation of eNOS in resistance arteries may modify the ET and renin-angiotensin system mediated vascular remodelling [35].…”

“…Although eNOS expression increases after exposure to hypoxia for 2 days and remained elevated at 7 and 14 days exposure in the conduit artery, the expression progressively increased after 7 and 14 days exposure in resistance arteries [34,35]. These findings suggest that up-regulation of eNOS in resistance arteries may modify the ET and renin-angiotensin system mediated vascular remodelling [35].…”