OBJECTIVETo study the effects of swimming exercise on the expression of apelin and its receptor (APJ) system in pulmonary tissues of rats with pulmonary hypertension induced by hypoxia.

METHODSForty-five male SD rats were randomly divided into control group, hypoxia group (seven-week) and swimming group (four-week swimming group after three-week hypoxia). The animal model of hypoxic pulmonary hypertension was established by exposing the rats to isobaric hypoxic chamber (8 h/d, 6 d/w). The rats of swimming group swam 60 min/day, 7 d/week for 4 weeks after three-week hypoxia. The mean pulmonary arterial pressure (mPAP) and the mean carotid arterial pressure (mCAP) were measured by either right or left cardiac catheterization, and the weight ratio of right ventricule/left ventricle plus septum [RV/(LV + S)] were calculated. The Masson's trichrome stained lung specimens were used by light microscope to examine the vessel wall area/total area (WA/TA), vessel cavity area/total area (CA/TA) and media thickness of pulmonary arterioles (PAMT). Meanwhile, apelin/ APJ expressions were determined by Western blot and immunohistochemistry.

RESULTS(1) mPAP and RV/(LV + S) of hypoxia group were higher than those of control group by 73.6% and 31.2% (P < 0.01), and mPAP and RV/(LV + S) of swimming group were lower than those of hypoxia group by 21.1%and 8.9 % (P < 0.05), respectively. (2) Masson's trichrome staining revealed that WA/TA and PAMT of hypoxia group were higher than those of control group by 70.8% and 102%. However, WA/TA and PAMT of swimming group were lower than those of hypoxia group by 24.8% and 40.1% (all P < 0.01), respectively. CA/TA of hypoxia group was lower than that of control group by 15.1%, and CA/TA of swimming group was lower than that of hypoxia group by 10.3% (all P < 0.01). (3) Compared with control group, hypoxia group showed up-regulated apelin expression and down-regulated APJ expression in pulmonary tissues (all P < 0.01). Compared with hypoxia group, swimming group showed decreased apelin expression and elevated APJ expression in pulmonary tissues (all P < 0.01). (4) Apelin localized mainly in intracytoplasm of inflammatory cell and tunica adventitia of vessel, and APJ were in vascular intima and tunica externa and plasmalemma of inflammatory cell.

CONCLUSIONThe improving effect of swimming exercise on hypoxic pulmonary hypertension in rats could be mediated by regulating the pulmonary apelin/APJ system.