| Objective: To observe the early manifestations of radiation induced heart damage(RIHD), and to explore the potential mechanisms in a rat model of RIHD, and further to examine cardioprotective effects of pretreatment with chronic intermittent hypobaric hypoxia(CIHH) on RIHD.Methods: Male adult Sprague-Dawley(SD) rats were randomly divided into four groups: Control Group, CIHH Group, Radiation Group and CIHH + radiation Group. A total of welve rats were in each group.1 Radiation: Rats received local heart irradiation with a single fraction of 20.0 Gy(at a dose rate of 1.8 Gy/min) from a precise type medical high-energy linear accelerator producing 6 MV X-ray and were freely housed two weeks after irradiation.2 CIHH pretreatment: Before irradiation, rats were treated with CIHH in a hypobaric chamber which mimicked 5000 m altitude(PB = 404 mm Hg, PO2 = 84 mm Hg, 6 hrs/day) for 28 consecutive days.3 Assessment on cardiac function: Langendorff perfusion technique was used to examine left ventricular function in isolated rat hearts after 30 minutes global no-flow ischemia, followed by 120 minutes of reperfusion. Parameters, including left ventricular developing pressure(LVDP), left ventricular end- diastolic pressure(LVEDP), the maximal differentials of left ventricular pressure(LVdp/dtmax) and coronary flow(CF), were continuously recorded. The rat hearts were removed quickly, followed by frozen at-20℃ for 24 hours once the reperfusion ceased. 2,3,5-triphenyltetrazolium chloride(TTC) staining was then performed for visualization of the unstained infarct regions.4 Histopathological evaluation: Alterations of mophorological structure of myocardial or interstitial tissues were examined by HE staining and the distribution of collagen fiber was analyzed by Masson staining.5 Biochemical procedures in rat cardiac tissues: The expression levels of the marker of fibrosis Collagen Type Ⅰ(COL-1) as well as markers of endoplasmic reticulum stress GRP78 and CHOP were quantitatively analyzed by Western blot. The activity of total superoxide dismutase(T-SOD) and content of lipid peroxide mylondialdehyde(MDA) were determined by ELISA.Results:1 Cardiac function in isolated rat hearts: Under the basic condition, CF was reduced from 12.56 ± 0.52ml/min to 8.90 ± 0.81ml/min(P < 0.05) following radiation but such an effect was inhibited(from 5.64 ± 0.35ml/min to 8.38 ± 0.52ml/min, P<0.05) by CIHH prior to radiation. Whereas other parameters of cardiac function were unchaged significantly(P>0.05). Actually, ischemia/reperfusion(I/R) induced damage of cardiac function. However, according to the alterations of parameters including LVDP, ±LVdp/dtmax and LVEDP, the recovery degree of cardiac function from I/R in radiation group was worse than that in Control Group but to a large extent was improved by CIHH pretreatment. In addition, the myocardial infarct size was significantly larger in Radiation Group than that in Control Group(P<0.01) but the in Pfarct size in CIHH + radiation Group was smaller compared with Radiation group(P<0.05).2 Histopathological evaluation:(1) HE staining from paraffin section: Irradiation induced significantly myocardial degeneration, nucleus mild contraction accompanied by interstitial inflammatory cells invasion but no necrosis. Pretreatment with CIHH to some extent improved damages as mentioned above.(2) Masson’s trichrome staining: All the collagen fiber was stained as light green, especially at the perivascular area and interstitial tissue. As a result of quantitative analysis, radiation induced a significant increase of collagen volume fraction(P<0.05) but such a deposition of collagen was reduced by CIHH pretreatment(P<0.05).3 ELISA and Western blot:(1) ELISA: The activity of T-SOD and content of MDA both were increased by irradiation(P<0.05 for both) but the latter was decreased after pretreatment with CIHH(P<0.05) whereas T-SOD was significantly increased(P<0.05).(2) Western blot: The levels of GRP78 and CHOP were increased by irradiation(P<0.05 for both) but decreased by CIHH pretreatment(P<0.05 for both). Additionally, irradiation resulted in the upregulation of COL-1(P<0.05) but such an enhancement was prohibited by CIHH pretreatment(P<0.05).Conclusions:1 Radiation induced damages of cardiac coronary artery. Irradiation had no influence on cardiac function under basic conditions but depressed the cardiac tolerance ability against ischemia/reperfusion(I/R) damage and increased myocardial infarct size.2 Radiation induced acute histopathological damages in rat hearts mainly including myocardial degeneration, interstitial inflammation, collagen deposition at the perivascular and interstitial regions.3 The potential mechanisms of RIHD might be attributed to oxidative stress, ER stress and fibrosis.4 Pretreatment with CIHH to a certain degree had beneficial effects on radiation induced damages of cardiac coronary artery and the cardiac tolerance ability against ischemia/reperfusion(I/R) damage. It decreased myocardial infarct size and improved the morphological damages including myocardial degeneration, interstitial inflammation, collagen deposition at the perivascular and interstitial regions. It could be suggested that such damages occurred at the acute stage of RIHD and to some extent was able to be improved by CIHH pretreatment, which exerted a protective effect by interfering with oxidative stress, endoplasmic reticulum stress and fibrosis. |
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