Opioid receptors mediate enhancement of ACh-induced aorta relaxation by chronic intermittent hypobaric hypoxia / 生理学报

The present study was designed to investigate the role of opioid receptors in the vasorelaxation effect of chronic intermittent hypobaric hypoxia (CIHH) in thoracic aorta rings and the underlying mechanism in rats. Adult male Sprague-Dawley (SD) rats were randomly divided into 2 groups: CIHH treatment group and control group. The rats in CIHH group were exposed to hypoxia in a hypobaric chamber (simulated 5 000 m altitude) for 28 days, 6 h per day. The rats in control group were kept in the same environment as CIHH rats except no hypoxia exposure. The relaxation of thoracic aorta rings was recorded by organ bath perfusion technique, and expression of opioid receptors was measured by Western blot. Results are shown as follows. (1) The acetylcholine (ACh)-induced endothelium-dependent relaxation of thoracic aorta in CIHH rats was increased obviously in a concentration-dependent manner compared with that in control rats (P < 0.05). (2) This enhancement of ACh-induced relaxation in CIHH rats was abolished by naloxone, a non-specific opioid receptor blocker (P < 0.05). (3) The expressions of δ, μ and κ opioid receptors in thoracic aorta of CIHH rats were up-regulated compared with those in control rats (P < 0.05). (4) The enhancement of CIHH on relaxation of thoracic aorta was reversed by glibenclamide, an ATP-sensitive potassium channel (KATP) blocker (P < 0.05). The results suggest that opioid receptors are involved in CIHH-enhanced ACh-induced vasorelaxation of thoracic aorta through KATP channel pathways.

Beneficial effects of intermittent hypobaric hypoxia on the body / 中国应用生理学杂志

Myocardial ischemia and reperfusion (I/R) is a common problem in clinic and there is no satisfactory method for prevention or treatment of I/R injury so far. Chronic intermittent hypobaric hypoxia (CIHH), similar to the concept of ischemia preconditioning (IPC)or altitude hypoxia adaptation (AHA), has been recognized to confer a protective effect on heart against I/R injury with a longer protective effect than IPC and a less adverse effect than AHA. It has been proved that CIHH increases myocardial tolerance to ischemia or hypoxia, reserving cardiac function and preventing arrhythmia during I/R. Multiple mechanisms or pathway underlying the cardiac protection of CIHH have been proposed, such as induction of heat-shock protein, enhancement of myocardial antioxidation capacity, increase of coronary flow and myocardial capillary angiogenesis, activation of adenosine triphosphate (ATP)-sensitive potassium channels, inhibition of mitochondrial permeability transition pores, and activation of protein kinase C (PKC) and induced nitric oxide synthase (iNOS). In addition, CIHH has been found having many beneficial effects on the body, such as promotion of health, increase of oxygen utilization, and prevention or treatment for some diseases. The beneficial effects of CIHH and potential mechanisms are reviewed mainly based on the researches performed by our group.

Effect of chronic intermittent hypobaric hypoxia on contractile activity of arteries in rats / 生理学报

The present study is aimed to investigate the effect of chronic intermittent hypobaric hypoxia (CIHH) on contractile activities in isolated thoracic aorta and pulmonary artery rings and the underlying mechanism in rats. Sprague-Dawley (SD) rats were randomly divided into 4 groups: control group (CON), 14 days CIHH treatment group (CIHH14), 28 days CIHH treatment group (CIHH28) and 42 days CIHH treatment group (CIHH42). CIHH rats were exposed to hypoxia in a hypobaric chamber simulating 5 000 m altitude, 6 h daily for 14, 28 and 42 d, respectively. After artery rings were prepared from pulmonary artery and thoracic aorta, the contractile activity of the artery rings was recorded using organ bath technique. Results are shown as follows. (1) There were no significant differences of noradrenaline (NA)- and KCl-induced contractions in thoracic aorta and pulmonary artery rings among CIHH and CON rats. (2) Angiotensin Ⅱ (ANGⅡ)-induced contraction in thoracic aorta rings, not in pulmonary artery rings, of CIHH rats was decreased compared with that in CON rats. There was no significant difference of ANGⅡ-induced contraction in thoracic aorta rings among CIHH rats. (3) Inhibitory effect of CIHH on ANGⅡ-induced contraction in thoracic aorta rings was endothelium-independent, and was reversed by glibenclamide (Gli), an ATP-sensitive potassium channels (K(ATP)) blocker, and L-NAME, a NO synthase inhibitor, but not by indomethacin (Indo), a cyclooxygenase inhibitor. These results suggest that CIHH attenuates the contraction induced by ANGⅡ in thoracic aorta rings of rat, which is related to the opening of K(ATP) channel and the increased production of NO.

Effects of chronic intermittent hypobaric hypoxia on immune function in rat / 中国应用生理学杂志

<p><b>AIM</b>To elucidate the effect of CIHH on cellular immunity and humoral immunity in rat by using flow cytometry method, immunohistochemistry method and electron microscopy techniques.</p><p><b>METHODS</b>Forty-eight male adult Sprague-Dawley rats were randomly divided into 4 groups: control(CON) group, 14 days CIHH (CIHH14) group, 28 days CIHH (CIHH28) group, 42 days CIHH (CIHH42) group. The animals in CIHH groups were exposed to 14, 28 and 42 days hypobaric hypoxia(simulated 3 000 m altitude, 5 h per day), respectively. Half of the animals in each group was treated with normaxia and the other half animals were treated with acute hypoxia for 1 h. CD3, CD4, CD8 T lymphocytes, natural killer (NK) cells, IgG, cortisol, epirenamine and C-reactive protein were examined. The weight and ultrastructure of thymus and spleen were observed.</p><p><b>RESULTS</b>(1) Compared with CON, both indexes of thymus and spleen in CIHH14 rats were increased significantly. Spleen index, but not thymus index, was increased in CIHH28 and CIHH42 rats. The thymocytes and spleen cytes in rat were injuryed during acute hypoxia, but the damage in CIHH rats was significant slighter than that in CON rats. (2) Compared with CON, CIHH28 and CIHH42, CD8 in CIHH14 rats were decreased, ratios of CD4/CD8 was increased and NK was decreased. (3) The rats of CON during acute hypoxia showed that CD4 was increased, CD8 was decreased, ratio of CD4/CD8 was elevated, and NK was increased. But there were no significant changes of CD3, CD4, CD8 and NK in CIHH28 and CIHH42 animals during acute hypoxia. (4) Compared with CON, CIHH28 and CIHH42, cortisol in CIHH14 rats was increased obviously, Epirenamine, cortisol and C-reactive protein in CON rats were increased, but there were no obvious changes in CIHH rats before and after acute hypoxia.</p><p><b>CONCLUSION</b>CIHH protects the immune function of rat against acute hypoxia, which is related with the regulation of neuroendocrine.</p>

Effect of chronic intermittent hypobaric hypoxia on α(1)-adrenergic receptor of myocardium participates in the cardioprotection / 生理学报

The purpose of the present study was to investigate the effect of chronic intermittent hypobaric hypoxia (CIHH) on α(1)-adrenergic receptors and the role of alpha(1)-adrenergic receptors in the protection of CIHH against ischemic injury of myocardium. Sixty-six adult male Sprague-Dawley rats were randomly divided into four groups: control group (Con), 14-day CIHH treatment group (CIHH14), 28-day CIHH treatment group (CIHH28) and 42-day CIHH treatment group (CIHH42). CIHH rats were exposed to hypoxia mimicking 5 000 m altitude (p(B)=404 mmHg, p(O(2))=84 mmHg) in a hypobaric chamber, 6 h daily for 14, 28 and 42 d, respectively. Control animals lived in the same environment as CIHH animals except hypoxia exposure. After anesthesia with sodium pentobarbital (3.0-3.5 mL/kg body weight, i.p.), papillary muscle was taken from the right ventricle of rat and perfused with modified Tyrode's solution continuously, at constant temperature (37 °C) and perfusion speed (12 mL/min). Muscle contraction was evoked by electric stimuli. Different concentrations (1x10(-7), 1x10(-6) and 1x10(-5) mol/L) of phenylephrine (PE), an alpha(1)-adrenergic receptor agonist, were applied cumulatively to investigate the effect of PE on the mechanic contraction of right ventricular papillary muscles of rats in Con, CIHH14, CIHH28 and CIHH42 groups. Also, prazosin (1x10(-6) mol/L), an α(1)-adrenergic receptor antagonist, was used to investigate the role of α(1)-adrenergic receptor in the protective effect of CIHH on papillary muscle. The results showed: (1) PE increased the maximal isometric tension (P(max)) and maximal velocity of tension development (P(dT/dt)) of muscle contraction in a dose-dependent manner (P<0.05), and the increase of the muscle contraction was much greater in CIHH28 and CIHH42 rats than that in Con rats (P<0.05). Under 1x10(-5) mol/L of PE, the increases of P(max) and P(dT/dt) over the baseline were 51.2% and 44.5% in CIHH28 group, 48.6% and 44.5% in CIHH42 group, and 28.7% and 24.5% in Con group, respectively; (2) The contraction of papillary muscle decreased during simulated ischemia, but the decrease was slighter in CIHH rats than that in Con rats (P<0.05). The decreases in P(max) and P(dT/dt) were 59.6% and 53.6% in CIHH28 group, 60.4% and 49.9% in CIHH42 group, and 74.4% and 64.7% in Con group, respectively; (3) The protective effect of CIHH on ischemic papillary muscle was abolished by prazosin (1x10(-6) mol/L). The results of the present study suggest that CIHH increases the activity of α(1)-adrenergic receptor, which is possibly one of the mechanisms for the cardioprotection of CIHH.

Comparison of the effects of chronic intermittent hypobaric hypoxia and continuous hypobaric hypoxia on hemodynamics in rats / 生理学报

The aim of this study is to investigate the effects of chronic intermittent hypobaric hypoxia (IHH) and chronic continuous hypobaric hypoxia (CHH) on hemodynamics under basic normoxia and acute hypoxia conditions and to find the difference of two types of chronic hypoxia. Forty adult male Sprague-Dawley (SD) rats were randomly divided into 5 groups: Control group (CON), 28 days IHH group (IHH28), 42 days IHH group (IHH42), 28 days CHH group (CHH28) and 42 days CHH group (CHH42). The rats in IHH groups were treated with intermittent hypoxia (11.1% O2) mimicking 5 000 m altitude in a hypobaric chamber for 28 or 42 d, 6 h a day, respectively. The rats in CHH groups lived in the hypobaric chamber with the same degree of hypoxia like IHH rats except half an hour in normoxia each day for feeding and cleaning. The body weight of rats was measured once a week. The parameters in hemodynamics, such as mean artery blood pressure (MAP), heart rate (HR), left ventricular systolic pressure (LVSP), maximum change rate of left ventricular pressure (+/-LVdP/dt(max)) were recorded under basic normoxia and acute hypoxia conditions through catheterization technique. The superoxide dismutase (SOD) activity and malondialdehyde (MDA) content in myocardium of rats were measured by biochemical method. The weights of whole heart, left and right ventricles were measured separately. The results showed: (1) The basic HR and MAP in CHH42 rats were lower than those in CON, IHH and CHH28 rats (P<0.05). (2) IHH showed a cardioprotection against acute hypoxia and reoxygenation injury, manifested as the result that the changes of HR, MAP, LVSP, and +/- LVdP/dt(max) were smaller than those in CON rats during acute hypoxia and reoxygenation. CHH showed a rather strong cardioprotection during acute hypoxia, manifested as the result that the decreases of HR, MAP, LVSP, and +/- LVdP/dt(max)were much smaller, but it did damage during reoxygenation, manifested as the result that the recovery of hemodynamics was the worst among three groups (P<0.05). (3) The antioxygenation of heart was increased in both IHH and CHH rats compared with that in CON rats manifested by the increased SOD activity and decreased MDA content (P<0.05, P<0.01). (4) IHH had no effect on heart weight, but CHH rats showed an obvious right ventricular hypertrophy compared with CON and IHH animals (P<0.01). The result indicates that IHH can induce a more effective cardioprotection with no much side effect, which might have a potential value for practical use.

The cardioprotection of intermittent hypoxic adaptation / 生理学报

Intermittent hypoxia (IH), or periodic hypoxia is referred as exposure to hypoxia interrupted by normoxia that occurs under many physiological and pathophysiological conditions. A lot of researches showed that IH adaptation, like ischemic preconditioning (IPC) and long-term high-altitude hypoxic adaptation (LHA), had significant cardioprotective effects including increasing the tolerance of myocardium to ischemia/reperfusion injury, limiting infarction size and morphologic damage, inhibiting apoptosis of myocardial cells, enhancing recovery of cardiac function in ischemia/reperfusion, and antiarrhythmia. However, the precise mechanisms underlying the protective effects of IH against ischemia/reperfusion injury are far from clear. The potential candidates participating in the protective effects of IH include oxygen transport, energy metabolism, neurohumoral regulation, antioxidase, stress protein, adenosine, ATP-sensitive potassium channel, mitochondrion, calcium control, nitric oxide and protein kinase. The effects of IH are affected by the protocol of hypoxic exposure, age and sex of experimental animals. IH adaptation, for longer lasting time than IPC and lesser side effect than LHA, might have a practical value for using.

Effects of different modes of intermittent hypobaric hypoxia on ischemia/reperfusion injury in developing rat hearts / 生理学报

The aim of the present study was to explore the effects of two different modes of intermittent hypobaric hypoxia (IHH) on myocardial ischemia/reperfusion injury in developing rat hearts. Postnatal male sprague-Dawley rats (n=72) were divided randomly into 3 groups: intermittent hypoxia at 3 000 m (IHH3000) group, intermittent hypoxia at 5 000 m (IHH5000) group and control group. The isolated hearts were perfused in the Langendorff apparatus, undergoing 30 min of global ischemia and 60 min of reperfusion. Cardiac function, coronary flow and lactate dehydrogenase (LDH) activity were recorded at 5 min before ischemia and 1, 5, 10, 20, 30, 60 min during reperfusion, respectively. The heart weight was measured at the end of the experiment. The results showed that: (1) There was no difference in body weight gaining between IHH3000 and control groups. The gain of body weight in IHH5000 group was much lower than that in IHH3000 and control groups (P<0.01). (2) Compared with that in the control group, the recovery of cardiac function in IHH3000 group was enhanced at 60 min after ischemia/reperfusion, coronary flow was increased, and LDH activity was decreased (P<0.05), meaning a cardioprotective effect occurred. There was no significant difference in heart weight between IHH3000 and control groups. In addition, cardiac function restored better in IHH3000 group after 42 d of hypoxic exposure than that after 28 d of hypoxic exposure (P<0.05). (3) Compared with that in the control group, the recovery of cardiac function in IHH5000 group was lower, coronary flow was decreased, and LDH activity was increased (P<0.05). There was a hypertrophy in the right ventricle in IHH5000 group. All changes indicated definitely that a detrimental effect developed in IHH5000 group. The results suggest that proper IHH can protect developing rat hearts against ischemia/reperfusion injury while this effect could be affected by the modes of intermittent hypoxic exposure.

Inhibitors of Na+/H+ and Na+/Ca2+ exchange depress intracellular calcium elevation induced by ischemia/reperfusion in rat cardiac myocytes / 生理学报

An increase in cytosolic free calcium has been shown to occur during ischemia in perfused hearts and plays a pivotal role in ischemia/reperfusion injury. The objective of this study was to investigate the contributions of Na(+)/H(+) exchange and Na(+)/Ca(2+) exchange to changes in intracellular calcium ([Ca(2+)](i)) during simulated ischemia and reperfusion in quiescent isolated rat cardiac myocytes. [Ca(2+)](i) was measured by laser confocal microscope using the fluorescent indicator Fluo 3 and expressed as the corrected intensity of Fluo 3 fluorescence. [Ca(2+)](i) increased to 140.3+/-13.0% (P<0.05 vs preischemic control 100%) after 5 min simulated ischemia, and remained at high level of 142.8+/-15.5% (P<0.05) after the following 15 min reperfusion. The increase in [Ca(2+)](i) during simulated ischemia and reperfusion was suppressed by 100 micromol/L amiloride (inhibitor of Na(+)/H(+) exchanger), 5 mmol/L NiCl2 (inhibitor of Na(+)/Ca(2+) exchanger) and calcium-free solution; [Ca(2+)](i) was 101.4+/-16.3%, 110.4+/-11.1% and 107.1+/-10.8%, respectively, after 5 min simulated ischemia, and 97.8+/-14.3%, 106.2+/-14.5% and 106.6+/-15.7%, respectively, after 15 min reperfusion. Compared with control cells, the amplitude of spontaneous calcium oscillation was lessened in cells treated with Ca-free perfusion and NiCl2 during reperfusion. In addition, no calcium oscillation was observed in cells pretreated with amiloride. These results suggest that Na(+)/H(+) exchange and Na(+)/Ca(2+) exchange are activated during simulated ischemia in isolated quiescent cardiac myocytes, leading to the elevation of [Ca(2+)](i) induced by simulated ischemia and reperfusion.