AIM: To determine the effect of intermittent hypoxia (IH) precondition on ischemic myocardium by using a rabbit model of chro nic myocardial ischemia with left anterior descending (LAD) banding. METHODS: Male, adult New Zealand white rabbits were assigned into three groups randomly. (1) normal group (N group), (2) control group (C group), (3) IH precondition group (H group). A LAD band was placed in C and H group firs t. The rabbits in H group were exposed to altitude of 5 000 m, for 6 h/day c ontin uously. According to IH precondition duration, the animals were subdivided into 7-days group (H1) and 42-days group (H2). After these experiments, the mRNA conc entrations of vascular endothelial growth factor (VEGF), hypoxia induced factor (HIF-1?), endothelial nitric oxide synthase (eNOS) and the expression of VEGF p rotein were detected. Tissue sections were stained for alkaline phosphatase with indoxyl-tetrazolium method to detect capillary density. RESULTS: The mRNA levels of VEGF, HIF-1?, eNOS and expression V E GF protein were increased in H group significantly. Compared with C and N group, the capillary density in H group was increased significantly. CONCLUSION: IH precondition increases angiogenesis in chronic is chemic myocardium in rabbits.

AIM: To investigate the effect of chronic intermittent hypobaric hypoxia (CIHH) on the activity of adrenergic receptor(AR) in rabbit sino-atrial node (SAN) by intracellular recording.METHODS: New Zealand rabbits were randomly divided into three groups: control group (Con), 14 d CIHH treatment group (CIHH14) and 28 d CIHH treatment group (CIHH28). The CIHH rabbits were exposed to a simulated 5 000 m (oxygen 11.1%) hypobaric hypoxia in hypoxic chamber for 14 d or 28 d (6 h/d), respectively. SAN preparation was used and the transmembrane action potential was recorded by micropipettes. Isoproterenol hydrochloride (ISO, agonist of β-AR) and phenylephrine (PE, agonist of α_1-AR) at different concentrations (0.01, 0.1 and 1 μmol/L) were applied cumulatively to investigate the electrophysiological effect of the drugs on the rabbit SAN among Con, CIHH14 and CIHH28 groups, respectively. RESULTS: (1) CIHH didnt change the parameters of action potential of SAN recorded under basic condition. (2) ISO changed some parameters of AP significantly in a dose-dependent manner, including increases in the amplitude of AP (APA), maximal rate of depolarization (V_(max)), the velocity of diastolic (phase 4) depolarization (VDD), and rate of pacemaker firing (RPF). (3) The response of AP to ISO in CIHH rabbits was decreased significantly compared to that in Con animals. Under 1 μmol/L of ISO, the increases in VDD, RPF, APA and V_(max) in CIHH animals were smaller than those in Con animals (P<0.05). (4) No effect of PE (0.01, 0.1 and 1 μmol/L) on the parameters of action potential was observed. CONCLUSION: CIHH decreases the reactivity of β-AR, but has no effect on α_1-AR in SAN of rabbit.