Acute hypobaric hypoxia and cardiac energetic response in prepubertal rats: Role of nitric oxide

Differences in mitochondrial function between brain and heart of senile rats exposed to acute hypobaric hypoxia. Role of nitric oxide

Rat brain and heart display different endogenous protective responses against hypobaric hypoxia in an age-dependent way. The aim of the present work was to evaluate the effects of acute hypobaric hypoxia (HH, 48 h) on brain and heart mitochondrial function as well as the participation of nitric oxide (NO) in old rats (22-month old). Cortical mitochondria from rats exposed to HH decreased respiratory rates (37 %, state 3) and membrane potential (20 %), but NO and H₂O₂ production increased by 48 %, and 23 %, respectively. Hippocampal mitochondria preserved O₂ consumption and H₂O₂ production, decreased membrane potential (18 %) and increased NO production (46 %). By contrast, HH decreased NO production (53 %) in mitochondria from left heart ventricles associated with increased cytochrome oxidase activity (39 %) and decreased NADPH oxidase activity (31 %). Also, a tendency to increase complex I-III (24 %) and complex II-III (65 %) activity was observed. In conclusion, after HH hippocampal and cortical mitochondria showed mild uncoupling and increased NO production. However, only the hippocampus preserved O₂ consumption and H₂O₂ levels. Interestingly, heart mitochondria showed a decreased ROS production through increased cytochrome oxidase activity associated with a decrease in NO production. This may be interpreted as a self-protective mechanism against hypoxia.

Systemic Blood Predictors of Elevated Pulmonary Artery Pressure Assessed by Non-invasive Echocardiography After Acute Exposure to High Altitude: A Prospective Cohort Study

Aim

Elevated pulmonary artery pressure (ePAP) in response to high-altitude hypoxia is a critical physiopathological factor in the hypoxic adaptation that may lead to high-altitude pulmonary edema in the acute phase or high-altitude pulmonary hypertension in the long term. However, the sea-level predictors of risk factors for altitude-induced ePAP have not been examined. Thus, we aimed to identify the baseline systemic blood predictors of ePAP after acute high-altitude exposure.

Materials and Methods

A total of 154 participants were transported to a high altitude 3,700 m from sea level within 2 h. Echocardiography examinations were performed to assess the mean pulmonary artery pressure (mPAP) and hemodynamics at both altitudes. All the individuals underwent blood tests to determine the concentrations of vascular regulatory factors. Univariate and adjusted logistic regression analyses were performed to identify the independent predictors of ePAP and factors related to ePAP.

Results

The mPAP increased significantly from sea level to high altitude (19.79 ± 6.53–27.16 ± 7.16 mmHg, p < 0.05). Increased levels of endothelin (ET-1), Ang (1–7), Ang II, and bradykinin were found after high-altitude exposure, while the levels of nitric oxide (NO), prostaglandin E2 (PEG2), and serotonin decreased sharply (all p-values < 0.05). At high altitude, 52.6% of the subjects exhibited ePAP, and the mPAP was closely correlated with the baseline Ang II level (r = 0.170, p = 0.036) and follow-up levels of NO (r = −0.209, p = 0.009), Ang II (r = 0.246, p = 0.002), and Ang (1–7) (r = −0.222, p = 0.006) and the left atrial inner diameter (LAD, r = 0.270, p < 0.001). Both the baseline and follow-up NO and Ang II levels were significantly different between the ePAP and non-ePAP groups. Finally, we identified the baseline Ang II and NO concentrations as two independent predictors of ePAP (p < 0.05). We also found that two vascular regulatory factors with inverse roles, namely, Ang (1–7) and Ang II, at high altitudes were independently associated with ePAP. Additionally, ET-1, NO, PEG2, and LAD were associated with ePAP.

Conclusion

The baseline concentrations of Ang II and NO at sea level are two independent predictors of ePAP after acute high-altitude exposure. Furthermore, Ang (1-7) and Ang II combined with ET-1, NO, PEG2, and LAD at high altitudes may contribute to the development of ePAP.