[Effect of NO on automaticity of rabbit sino-atrial node].

AIM: To investigate the effects of exogenous NO donors sodium nitroprusside (SNP) and 3-morpholinosydnonimine (SIN-1) on automaticity of the rabbit sino-atrial node in vitro and the action mechanism. METHODS: The intracellular microelectrode technique is used to record the action potentials of rabbit sino-atrial node and APA (amplitude of AP), V(max) (maximal rate of depolarization), VDD (velocity of diastolic depolarization), RPF (rate of pacemaker firing) are analyzed. RESULTS: SNP(10(-5) - 10(-2) mol/L) increased its RPF and VDD dose-dependently. 10(-3) mol/L SNP increased RPF (beats/min) from 163 +/- 10.8 to 195.0 +/- 13.1 increased VDD (mV/s) from 50.3 +/- 9.6 to 70.2 +/- 12.1 (P < 0.01). SIN-1(10(-3) - 10(-2) mol/L) also increased RPF and VDD (P < 0.01).10(-4) mo/L Methylene blue (MB), a blocker of GMP cyclase, prevented the positive chronotropic effect and increasement of VDD induced by 10(-3) mol/L SNP totally (P < 0.01). 2. CsCl (2 mmol/L), a blocker of I(f) prevented the increasement of RPF and VDD in part (P < 0.05). 3. NIF (0.46 micromol/L), a blocker of I(Ca-L, had no significant effects on chronotropic effect and increasement of VDD (P < 0.01). CONCLUSION: Exogenous NO can increase the automaticity of rabbit sino-atrial node in vitro. The chronotropic effect is involved in NO-cGMP pathway and results from increasement of I(f) in the sino-atrial node at least in part; I(ca-L) is unlikely to play a major role in this effect.

[The protective effects of ischemic preconditioning on reperfusion injury of rat lung].

AIM: To investigate the effects of ischemic preconditioning on reperfusion injury of rat lung. METHODS: Rat isolated lungs (n=8 in each group) were stabilized and perfused by Krebs-Henseleit solution on a modified langendorff perfusion apparatus. 36 wistar rats were divided into three groups: ischemic preconditioning group, ischemia/reperfusion group and control group. Mean pulmonary artery pressure, wet/dry ratio, pulmonary surfactant phospholipid and alveolar surface tension in bronchoalveolar lavage fluid and electron microscope were detected. RESULTS: The morphological changes of lung injury were alleviated in the preconditioning group under electron microscope. Wet/dry ratio, mean pulmonary artery pressure and SA/LA ratio were significantly lower in the preconditioning group after ischemic/reperfusion (P < 0.01). Total phospholipid and large aggregate in the BALF were significantly increased in the preconditioning group (P < 0.01). Small aggregate showed no change in three groups. Surfactant activity test showed that surface tension markedly decreased in IPC group (P < 0.01). CONCLUSION: These results indicates that ischemic preconditioning may have a protective effect in ischemic/reperfusion injuries lung by ameliorating the content and function of surfactant phospholipid.