ESTROGEN ALLEVIATES POSTHEMORRHAGIC SHOCK MESENTERIC LYMPH-MEDIATED LUNG INJURY THROUGH AUTOPHAGY INHIBITION.

ABSTRACT: Background: Hemorrhagic shock-induced acute lung injury (ALI) is commonly associated with the posthemorrhagic shock mesenteric lymph (PHSML) return. Whether excessive autophagy is involved in PHSML-mediated ALI remains unclear. The relationship between estrogen treatment and PHSML or autophagy needs to verify. The current study will clarify the role of estrogen in reducing PHSML-mediated ALI through inhibition of autophagy. Methods: First, a hemorrhagic shock model in conscious rats was used to observe the effects of 17ß-estradiol (E2) on intestinal blood flow, pulmonary function, intestinal and pulmonary morphology, and expression of autophagy marker proteins. Meanwhile, the effect of PHSML and autophagy agonist during E2 treatment was also investigated. Secondly, rat primary pulmonary microvascular endothelial cells were used to observe the effect of PHSML, PHSML plus E2, and E2-PHSML (PHSML obtained from rats treated by E2) on the cell viability. Results: Hemorrhagic shock induced intestinal and pulmonary tissue damage and increased wet/dry ratio, reduced intestinal blood flow, along with pulmonary dysfunction characterized by increased functional residual capacity and lung resistance and decreased inspiratory capacity and peak expiratory flow. Hemorrhagic shock also enhanced the autophagy levels in intestinal and pulmonary tissue, which was characterized by increased expressions of LC3 II/I and Beclin-1 and decreased expression of p62. E2 treatment significantly attenuated these adverse changes after hemorrhagic shock, which was reversed by PHSML or rapamycin administration. Importantly, PHSML incubation decreased the viability of pulmonary microvascular endothelial cells, while E2 coincubation or E2-treated lymph counteracted the adverse roles of PHSML. Conclusions: The role of estrogen reducing PHSML-mediated ALI is associated with the inhibition of autophagy.

POSTHEMORRHAGIC SHOCK MESENTERIC LYMPH IMPAIRS SPLENIC DENDRITIC CELL FUNCTION IN MICE.

ABSTRACT: Dendritic cell (DC)-mediated immune dysfunction is involved in the process of severe hemorrhagic shock that leads to sepsis. Although post-hemorrhagic shock mesenteric lymph (PHSML) induces immune organs injuries and apoptosis, whether PHSML exerts adverse effects on splenic DCs remains unknown. In this study, we established a hemorrhagic shock model (40 ± 2 mm Hg for 60 min) followed by fluid resuscitation with the shed blood and equal Ringer's solution and drained the PHSML after resuscitation. At 3 h after resuscitation, we harvested the splenic tissue to isolate DCs using anti-CD11c immunomagnetic beads and then detected the necrotic and apoptotic rates in splenocytes and splenic DCs. We also detected the levels of TNF-α, IL-10, and IL-12 in the culture supernatants and surface marker expressions of MHC-II, CD80, and CD86 of splenic DCs following LPS stimulation for 24 h. Second, we purified the DCs from splenocytes of normal mice to investigate the effects of PHSML treatment on cytokine production and surface marker expression following LPS stimulation. The results showed that PHSML drainage attenuated LPS-induced cell death of splenocytes and DCs. Meanwhile, PHSML drainage enhanced the DC percentage in splenocytes and increased the TNF-α and IL-12 production by DCs and the expressions of CD80, CD86, and MHCII of DCs treated by LPS. Furthermore, PHSML treatment reduced the productions of TNF-α, IL-10, and IL-12 and the expressions of CD80 and CD86 in normal DCs after treatment with LPS. In summary, the current investigation demonstrated that PHSML inhibited the cytokine production and surface marker expressions of DCs stimulated by LPS, suggesting that PHSML plays an important role in hemorrhagic shock-induced immunosuppression through the impairment of DC function and maturation.

Omega-3 polyunsaturated fatty acids alleviates lung injury mediated by post-hemorrhagic shock mesenteric lymph.

Severe hemorrhage-induced acute lung injury (ALI) remains the major contributor to critical patient mortality and is associated with posthemorrhagic shock mesenteric lymph (PHSML) return. Omega-3 polyunsaturated fatty acids (ω-3 PUFAs) play overall protection on acute hemorrhage, but a reliable mechanism needs to be identified. The aims of this study were to investigate the role of ω-3 PUFAs in alleviating ALI and whether is related to the endotoxin contained in PHSML. Mesenteric lymph was harvested from rats subjected to hemorrhagic shock (hemorrhage-induced hypotension of 40 ± 2 mmHg for 90 min plus by resuscitation) or sham shock. The effect of ω-3 PUFAs on pulmonary function, water content, morphology, and LBP, CD14, TNF-α, and IL-6 levels were observed in rats subjected to hemorrhagic shock, while the effect of PHSML intravenous infusion on the beneficial effect of ω-3 PUFAs also was investigated. In addition, the effect of ω-3 PUFAs on the endotoxin contents in mesenteric lymph were detected. Hemorrhagic shock-induced ALI was characterized by increased functional residual capacity (FRC), lung resistance (RI), inspiratory capacity (IC), respiratory frequency, water contents and structural damage, along with increases in LBP, IL-6, and TNF-α. ω-3 PUFAs treatment reduced FRC, RI, IC, frequency, water contents, LBP, IL-6, TNF-α, and alleviated morphological damage. In contrast, PHSML infusion abolished the advantageous effects of ω-3 PUFAs on the above indices and CD14. Furthermore, the endotoxin level of PHSML was significantly enhanced, but declined following ω-3 PUFAs administration. These findings together suggested that treatment with ω-3 PUFAs ameliorates hemorrhagic shock-induced ALI, which is associated with reduced endotoxin contained in PHSML.

TLR2/TLR4-Enhanced TIPE2 Expression Is Involved in Post-Hemorrhagic Shock Mesenteric Lymph-Induced Activation of CD4+T Cells.

Purpose: Post hemorrhagic shock mesenteric lymph (PHSML) return contributes to CD4+ T cell dysfunction, which leads to immune dysfunction and uncontrolled inflammatory response. Tumor necrosis factor α induced protein 8 like-2 (TIPE2) is one of the essential proteins to maintain the immune homeostasis. This study investigated the role of TIPE2 in regulation of CD4+ T lymphocyte function in interaction of PHSML and TLR2/TLR4. Methods: The splenic CD4+ T cells were isolated from various mice (WT, TLR2-/-, TLR4-/-) by immunomagnetic beads, and stimulated with PHSML, normal lymphatic fluid (NML), respectively. Application of TIPE2-carrying interfering fragments of lentivirus were transfected to WT, TLR4-/-, and TLR2-/- CD4+ T cells, respectively. After interference of TIPE2, they were stimulated with PHSML and NML for the examinations of TIPE2, TLR2, and TLR4 mRNA expressions, proliferation, activation molecules on surface, and cytokine secretion function. Results: PHSML stimulation significantly upregulated TIPE2, TLR2, and TLR4 mRNA expressions, decreased proliferation, CD25 expression, and IFN-γ secretion, and increased the secretion ability of IL-4 in WT CD4+ T cells. TIPE2 silencing enhanced proliferative capacity, upregulated CD25 expression, and increased IFNγ secretion in CD4+ T cells. PHSML stimulated TLR2-/-CD4+ T or TLR4-/-CD4+ T cells of which TIPE2 were silenced. TLR2 or TLR4 knockout attenuated PHSML-induced CD4+ T cells dysfunction; PHSML stimulation of silent TIPE2-expressing TLR2-/-CD4+ T or TLR4-/-CD4+ T revealed that the coexistence of low TIPE2 expression with lack of TLR2 or TLR4 eliminated this beneficial effect. Conclusion: TIPE2 improves the PHSML-mediated CD4+T cells dysfunction by regulating TLR2/TLR4 pathway, providing a new intervention target following hemorrhagic shock-induced immune dysfunction.

Stellate Ganglion Block Improves the Proliferation and Function of Splenic CD4 + T Cells Through Inhibition of Posthemorrhagic Shock Mesenteric Lymph-Mediated Autophagy.

Severe hemorrhagic shock leads to excessive inflammation and immune dysfunction, which results in high mortality related to mesenteric lymph return. A recent study showed that stellate ganglion block (SGB) increased the survival rate in rats suffering hemorrhagic shock. However, whether SGB ameliorates immune dysfunction induced by hemorrhagic shock remains unknown. The aim of the present study was to verify the favorable effects of SGB on the proliferation and function of splenic CD4 + T cells isolated from rats that underwent hemorrhagic shock and to investigate the mechanism related to the SGB interaction with autophagy and posthemorrhagic shock mesenteric lymph (PHSML). Male rats underwent SGB or sham SGB and conscious acute hemorrhage followed by resuscitation and multiple treatments. After 3 h of resuscitation, splenic CD4 + T cells were isolated to measure proliferation and cytokine production following stimulation with ConA in vitro. CD4 + T cells isolated from normal rats were treated with PHSML drained from SBG-treated rats, and proliferation, cytokine production, and autophagy biomarkers were detected. Hemorrhagic shock reduced CD4 + T cell proliferation and production of interleukin (IL)-2, IL-4, and tumor necrosis factor-α-induced protein 8-like 2 (TIPE2). SGB or administration of the autophagy inhibitor 3-methyladenine (3-MA) normalized these indicators. In contrast, administration of rapamycin (RAPA) autophagy agonist or intravenous injection of PHSML inhibited the beneficial effects of SGB on CD4 + T cells from hemorrhagic shocked rats. Furthermore, PHSML incubation decreased proliferation and cytokine production, increased LC3 II/I and Beclin-1 expression, and reduced p-PI3K and p-Akt expression in normal CD4 + T cells. These adverse effects of PHSML were also abolished by 3-MA administration, as well as incubation with PHSML obtained from SGB-treated rats. SGB improves splenic CD4 + T cell function following hemorrhagic shock, which is related to the inhibition of PHSML-mediated autophagy.

Estradiol-induced inhibition of endoplasmic reticulum stress normalizes splenic CD4 + T lymphocytes following hemorrhagic shock.

The aim is to investigate that 17ß-estradiol (E2)/estrogen receptors (ERs) activation normalizes splenic CD4 + T lymphocytes proliferation and cytokine production through inhibition of endoplasmic reticulum stress (ERS) following hemorrhage. The results showed that hemorrhagic shock (hemorrhage through femoral artery, 38-42 mmHg for 90 min followed by resuscitation of 30 min and subsequent observation period of 180 min) decreased the CD4+ T lymphocytes proliferation and cytokine production after isolation and incubation with Concanavalin A (5 µg/mL) for 48 h, induced the splenic injury with evidences of missed contours of the white pulp, irregular cellular structure, and typical inflammatory cell infiltration, upregulated the expressions of ERS biomarkers 78 kDa glucose-regulated protein (GRP78) and activating transcription factor 6 (ATF6). Either E2, ER-α agonist propyl pyrazole triol (PPT) or ERS inhibitor 4-Phenylbutyric acid administration normalized these parameters, while ER-ß agonist diarylpropionitrile administration had no effect. In contrast, administrations of either ERs antagonist ICI 182,780 or G15 abolished the salutary effects of E2. Likewise, ERS inducer tunicamycin induced an adverse effect similarly to that of hemorrhagic shock in sham rats, and aggravated shock-induced effects, also abolished the beneficial effects of E2 and PPT, respectively. Together, the data suggest that E2 produces salutary effects on CD4+ T lymphocytes function, and these effects are mediated by ER-α and GPR30, but not ER-ß, and associated with the attenuation of hemorrhagic shock-induced ERS.

Estrogen Enhances the Microvascular Reactivity Through RhoA-ROCK Pathway in Female Mice During Hemorrhagic Shock.

ABSTRACT: Vascular hypo-reactivity plays a critical role inducing organ injury during hemorrhagic shock. 17ß-estradiol (E2) can induce vasodilation to increase blood flow in various vascular beds. This study observed whether E2 can restore vascular hypo-reactivity induced by hemorrhagic shock, and whether E2 effects are associated with RhoA-Rho kinase (ROCK)-myosin light chain kinase phosphatase (MLCP) pathway. The hemorrhagic shock model (40 ±â€Š2 mm Hg for 1 h, resuscitation for 4 h) was established in ovary intact sham operation (OVI), ovariectomized (OVX), and OVX plus E2 supplement female mice. Intestinal microvascular loop was used to assess blood flow in vivo, mRNA expression and vascular reactivity in vitro. Hemorrhagic shock significantly reduced norepinephrine microvascular reactivity. Decreased microvascular reactivity was exacerbated by OVX and reversed by E2 supplement. U-46619 (RhoA agonist) increased microvascular reactivity, and C3 transferase (an ADP ribosyl transferase that selectively induces RhoA ribosylation) or Y-27632 (ROCK inhibitor) inhibited sham mice microvascular reactivity. Similarly, U-46619 increased microvascular reactivity in OVI and OVX mice following hemorrhagic shock, which was abolished by Y-27632 or concomitant incubation of okadaic acid (OA) (MLCP inhibitor) and Y-27632. In OVX plus E2 supplement mice with hemorrhagic shock, Y-27632 inhibited microvascular reactivity, which was abolished by concomitant U-46619 application. Lastly, hemorrhagic shock remarkably decreased intestinal loop blood flow, RhoA and ROCK mRNA expressions in vascular tissues in OVX females, but not in OVI females, which were reversed by E2 supplement. These results indicate that estrogen improves microvascular reactivity during hemorrhagic shock, and RhoA-ROCK signaling pathway may mediate E2 effects.

Mesenteric lymph drainage alleviates hemorrhagic shock-induced spleen injury and inflammation

Abstract Purpose: To investigate the effect of mesenteric lymph drainage on the spleen injury and the expressions of inflammatory cytokines in splenic tissue in mice following hemorrhagic shock. Methods: Male C57 mice were randomly divided into the sham shock, shock and shock+drainage groups. The mice in both shock and shock+drainage groups suffered femoral artery bleeding, maintained mean arterial pressure (MAP) of 40±2 mmHg for 90 min, and were resuscitated. And mesenteric lymph drainage was performed in the shock+drainage group at the time of resuscitation. After three hours of resuscitation, the splenic tissues were harvested for the histological observation and protein and mRNA expression analysis of cytokines. Results: The spleen in the shock group revealed a significantly structural damage and increased mRNA expressions of MyD88 and TRAF6 and protein expressions of TIPE2, MyD88, TRIF and TRAF3 compared to the sham group. By contrast, the splenic pathological injury in the shock+drainage group was alleviated significantly, and the mRNA and protein expressions of TIPE2, MyD88, TRIF, TRAF3 and TRAF6 were significantly lower than those in the shock group. Conclusion: These results indicate that post-hemorrhagic shock mesenteric lymph drainage alleviates hemorrhagic shock-induced spleen injury and the expressions of inflammatory cytokines.

Normal mesenteric lymph ameliorates lipopolysaccharide challenge-induced spleen injury.

PURPOSE: This study was conducted to investigate the effect of normal mesenteric lymph (NML) from mice on the spleen injury induced by lipopolysaccharide (LPS) challenge. METHODS: Mice in the LPS and LPS+NML groups received an intraperitoneal injection of LPS (35 mg/kg) and kept for 6 h.. The mice in the LPS+NML group received NML treatment at 1 h after LPS injection. Afterward, the splenic morphology, the levels of lipopolysaccharide-binding protein (LBP), cluster of differentiation 14 (CD14), phosphorylation mitogen-activated protein kinases (MAPKs), and inflammatory mediators in splenic tissue were investigated. RESULTS: LPS injection induced spleen injury, increased the levels of LBP, CD14, tumor necrosis factor-α (TNF-α), interleukin 6 (IL-6), and interferon γ (IFN-γ), and decreased the IL-4 content in the spleen. By contrast, NML treatment reversed these changes. Meanwhile, the LPS challenge decreased the phosphorylation levels of p38 MAPK, extracellular regulated protein kinases 1/2, and c-Jun N-terminal kinase (JNK). Moreover, the phosphorylation levels of p38 MAPK and JNK were further decreased by the NML administration. CONCLUSION: rRdThe normal mesenteric lymph treatment alleviated lipopolysaccharide induced spleen injury by attenuating LPS sensitization and production of TNF-α, IL-6, and IFN-γ.

Normal mesenteric lymph ameliorates lipopolysaccharide challenge-induced spleen injury

PURPOSE: This study was conducted to investigate the effect of normal mesenteric lymph (NML) from mice on the spleen injury induced by lipopolysaccharide (LPS) challenge.METHODS: Mice in the LPS and LPS+NML groups received an intraperitoneal injection of LPS (35 mg/kg) and kept for 6 h.. The mice in the LPS+NML group received NML treatment at 1 h after LPS injection. Afterward, the splenic morphology, the levels of lipopolysaccharide-binding protein (LBP), cluster of differentiation 14 (CD14), phosphorylation mitogen-activated protein kinases (MAPKs), and inflammatory mediators in splenic tissue were investigated.RESULTS:LPS injection induced spleen injury, increased the levels of LBP, CD14, tumor necrosis factor-α (TNF-α), interleukin 6 (IL-6), and interferon γ (IFN-γ), and decreased the IL-4 content in the spleen. By contrast, NML treatment reversed these changes. Meanwhile, the LPS challenge decreased the phosphorylation levels of p38 MAPK, extracellular regulated protein kinases 1/2, and c-Jun N-terminal kinase (JNK). Moreover, the phosphorylation levels of p38 MAPK and JNK were further decreased by the NML administration.CONCLUSION:rRdThe normal mesenteric lymph treatment alleviated lipopolysaccharide induced spleen injury by attenuating LPS sensitization and production of TNF-α, IL-6, and IFN-γ.

Post-hemorrhagic shock mesenteric lymph is an important contributor to cardiac dysfunction following hemorrhagic shock

PURPOSE: To evaluate whether post-hemorrhagic shock mesenteric lymph (PSML) is involved in cardiac dysfunction induced by hemorrhagic shock. METHODS: The hemorrhagic shock model (40±2 mmHg, 3h) was established in rats of the shock and shock+drainage groups; and PSML drainage was performed from hypotension 1-3h in the shock+drainage rats. Then, the isolated hearts were obtained from the rats for the examination of cardiac function with Langendorff system. Subsequently, the isolated hearts were obtained from normal rats and perfused with PSML or Krebs-Henseleit solution, and the changes of cardiac function were observed. RESULTS: The left ventricular systolic pressure (LVSP) and the maximal rates of LV developed pressure (LVDP) rise and fall (±dP/dt max) in the shock and shock+drainage groups were lower than that of the sham group; otherwise, these indices in the shock+drainage group were higher compared to the shock group. In addition, after isolated hearts obtained from normal rats perfusing with PSML, these cardiac function indices were gradual decline along with the extension of time, such as heart rate, LVSP, ±dP/dt max, etc. CONCLUSION: Post-hemorrhagic shock mesenteric lymph is an important contributor to cardiac dysfunction following hemorrhagic shock. .

Normal mesenteric lymph ameliorates acute kidney injury following lipopolysaccharide challenge in mice.

BACKGROUND: The kidney is one of the prior damaged organs subjected to severe infection and sepsis shock. Our previous studies have shown that the normal mesenteric lymph (NML) obtained from healthy dogs could alleviate multiple organ injuries following endotoxic shock. In the current study, we further investigated the beneficial effect of NML from healthy mice on acute kidney injury (AKI) induced by lipopolysaccharide (LPS) in mice. METHODS: The mice in LPS and LPS + NML groups received an intraperitoneal injection of LPS (35 mg/kg). One hour later, the treatment of NML was performed and kept for 6 h. Then, the renal function indices, renal morphology, the levels of phosphorylation mitogen-activated protein kinases (MAPKs), markers of sensitization to LPS, as well as pro-inflammatory mediators in renal tissue were observed. RESULTS: Intraperitoneal injection of LPS induced an increased level of urea in plasma, lipopolysaccharide-binding protein (LBP), cluster of differentiation 14 (CD14), tumor necrosis factor-α (TNF-α) and interleukin 6 (IL-6), but no obvious changes in the MAPKs in renal tissue. NML treatment decreased the levels of urea, CD14, TNF-α and IL-6 in mice after LPS injection. CONCLUSION: The current results indicate that NML alleviates LPS-induced AKI through its attenuation of sensitization to LPS.

[Role of mesenteric lymph drainage improving the metabolism of red blood cell in hemorrhagic shock rats following fluid resuscitation].

OBJECTIVE: To observe the effects of mesenteric lymph drainage on the metabolism of red blood cell (RBC) in hemorrhagic shock (HS) rats following fluid resuscitation. METHODS: Eighteen male Wistar rats were randomly divided into sham group (n=6), HS group (n=6), HS + drainage group (n=6). After 1.5 hours of HS model prepared, the animals were given fluid resuscitation by lost blood plus equal volume of Ringer solution within 30 minutes in HS and HS + drainage groups, and mesenteric lymph drainage was performed after 1 hour of hypotension in HS + drainage group. At 3 hours after resuscitation or corresponding time, blood samples were obtained from abdominal aorta. Membrane suspensions of RBC prepared from part of whole blood samples were used to measure the activities of adenosine triphosphate ase (ATPase) and contents of ATP and lactic acid (LA), the intracellular fluid of RBC prepared from part of whole blood samples was used to determine the concentration of 2,3-diphosphoglyceric acid (2,3-DPG), Na(+) and K(+), plasma samples isolated from blood by centrifugation were used to determine the concentration of Na(+), K(+), Cl(-) and total Ca. RESULTS: Compared with sham group, the content of ATP (µmol/g), activity of Na(+)-K(+)-ATPase (µmol×mg(-1)×h(-1)) and Ca(2+)-ATPase (µmol×mg(-1)×h(-1)) in RBC membrane and total Ca (mmol/L) in plasma were decreased markedly (ATP: 6.698±0.938 vs. 10.670±1.466, Na(+)-K(+)-ATPase: 0.042±0.010 vs. 0.066±0.019, Ca(2+)-ATPase: 0.054±0.015 vs. 0.081±0.017, total Ca: 2.27±0.18 vs. 2.66±0.21, P<0.05 or P<0.01) in HS group, and the content of LA (mmol/g) in RBC and K(+) (mmol/L), Cl(-) (mmol/L) in plasma were increased observably in HS group (LA: 3.472±0.853 vs. 1.743±0.395, K(+): 5.83±0.34 vs. 5.23±0.37, Cl(-): 113.37±3.63 vs. 106.35±4.99, P<0.05 or P<0.01), there was no significant difference in term of the contents of 2,3-DPG (mmol/L: 2.196±0.609 vs. 2.590±0.574, P>0.05). Compared with HS group, the contents of 2,3-DPG (4.459±0.900) and ATP (8.859±1.189), the activities of Na(+)-K(+)-ATPase (0.089±0.022), Ca(2+)-ATPase (0.082±0.020) of RBC were increased in HS + drainage group, and the level of LA (2.060±0.810) was decreased observably (P<0.05 or P<0.01), there were no significant differences in the other indices. CONCLUSIONS: The results indicate that shock mesenteric lymph drainage plays an important role in improving the metabolism of RBC in HS rats following fluid resuscitation, subsequently, may preserve the structure and function of RBC.

[Electrophysiological effects of antiarrhythmic drugs on pacemaker cells in guinea pig left ventricular outflow tract].

OBJECTIVE: To explore the electrophysiological effects of antiarrhythmic drugs on pacemaker cells of left ventricular outflow tract. METHODS: By using conventional intracellular microelectrode technique to record action potentials, series antiarrhythmic drugs were used to investigate the electrophysiological features and regularities of spontaneous activity of left ventricular outflow tract. RESULTS: (1) Perfusion with 1 micromol/L quinidine resulted in a significant decrease in rate of pacemaker firing (RPF, P < 0.05), velocity of diastolic depolarization (VDD, P < 0.05), amplitude of action potential (APA, P < 0.05), and maximal rate of depolarization (V(max), P < 0.05), and a marked prolonging in 50% and 90% of duration of action potential (APD50 and APD90, P < 0.05). (2) 1 micromol/L lidocaine decreased RPF, VDD, MDP, APA and V(max) significantly (P < 0.05), shortened APD50 and APD90 notably (P < 0.05). (3) 1 micromol/L propafenone led to a significant decrease in RPF (P < 0.01), VDD (P < 0.05), APA (P < 0.05), V(max) (P < 0.01), and a marked prolonging in APD50 (P < 0.01) and APD90 (P < 0.05). (4) Application of 5 micromol/L propranolol resulted in a significant decrease in RPF and VDD (P < 0.01), MDP and APA (P < 0.01), V(max) (P < 0.05) and a notable prolonging in APD50 and APD90 (P < 0.05). (5) Perfusion with 1 micromol/L amiodarone resulted in a significant decrease in RPF and VDD (P < 0.01), APA (P < 0.01), V(max) (P < 0.05), a marked prolonging in APD50 (P < 0.01) and APD90 (P < 0.05). (6) 1 micromol/L verapamil significantly decreased RPF and VDD (P < 0.01), MDP and APA (P < 0.05), V(max) (P < 0.05), notably prolonged APD50 and APD90 (P < 0.01). (7) 50 micromol/L adenosine significantly decreased RPF and VDD (P < 0.05), APA (P < 0.05), V(max) (P < 0.01), markedly shortened APD50 and APD90 (P < 0.05). CONCLUSION: All kinds of antiarrhythmic drugs can decrease the autorhythmicity of guinea pig left ventricular outflow tract. By altering APD50 and APD90, they can affect effective refractory period (ERP) and having a significant effect on autorhythmicity of left ventricular outflow tract.