Abstract
Although oxygen therapy rapidly improves arterial oxygen saturation in idiopathic pulmonary arterial hypertension, the effects of chronic administration of oxygen are unknown. The purpose of the present study was to investigate the effects of chronic oxygen therapy on the histological changes and survival rate in rats with idiopathic pulmonary arterial hypertension. Idiopathic pulmonary arterial hypertension was induced by monocrotaline injection. The rats were then randomly assigned to receive or not receive oxygen therapy (O2 group and non-O2 group, respectively). The rats in the O2 group were exposed to a high (90%) oxygen environment from day 17 following injection of monocrotaline, when hypoxemia was first observed. The pulmonary arteriole walls were significantly thicker in monocrotaline-injected rats than in saline-injected rats as vehicle on day 19 and were significantly thicker in the rats that received oxygen therapy than in the rats that did not. Right ventricular inflammations were significantly higher in monocrotaline-injected rats than in saline-injected rats on day 19 and were significantly higher in the rats that received oxygen therapy than in the rats that did not. By day 20 after injection of monocrotaline, the survival rate was significantly lower in the rats that received oxygen therapy than in those that did not. Superoxide dismutase activity in the lungs was higher in monocrotaline-injected rats than in saline-injected rats on day 19 after monocrotaline injection and was also higher in the saline-injected rats that received oxygen therapy than in the saline-injected rats that did not. No interaction was detected between monocrotaline injection and oxygen therapy. These results suggest that chronic oxygen therapy worsens the histological changes and survival rate in idiopathic pulmonary arterial hypertension. The fact that degradation of the histological changes and survival rate was accompanied by increase in superoxide dismutase activity suggests that antioxidant capacity may contribute to the degradation.
Highlights
Pulmonary arterial hypertension is characterized by progressive histological changes, including medial hypertrophy, intimal thickening, plexiform lesions, dilated lesions, and arteritis, in the pulmonary arteries and arterioles [1] that increase pulmonary arterial blood pressure
Chronic oxygen therapy prevented a decrease in oxygen saturation in rats with pulmonary arterial hypertension but caused weight loss and decreased the survival rate
We found that chronic oxygen therapy accelerated medial hypertrophy in the pulmonary arterioles induced by monocrotaline
Summary
Pulmonary arterial hypertension is characterized by progressive histological changes, including medial hypertrophy, intimal thickening, plexiform lesions, dilated lesions, and arteritis, in the pulmonary arteries and arterioles [1] that increase pulmonary arterial blood pressure. These histological changes cause narrowing of the luminal diameter of the pulmonary arteries and arterioles and decreased circulation of blood in the lungs. Oxygen therapy is often used to alleviate dyspnea, there is insufficient knowledge of the therapy for pulmonary arterial hypertension. The efficacy of oxygen therapy in COPD depends on severity of pulmonary arterial hypertension, suggesting that early treatment would improve the prognosis [10]. The pathogenic mechanisms differ between idiopathic pulmonary arterial hypertension and COPD-related pulmonary hypertension, oxygen therapy is performed based on limited knowledge of the therapy for COPD
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