Effect of ligustrazine on pulmonary arterial pressure and pulmonary arterial wall collagen of chronic hypoxic hypercapnic rats

AIM:To study the effect of ligustrazine on pulmonary hypertensive rats induced by hypoxic hypercapnia. METHODS:Thirty rats were randomly divided into three groups:control group(A),hypoxic hypercapnic group(B), hypoxic hypercapnia+ligustrazine(lig.) group(C). RESULTS: (1) Mean pulmonary arterial pressure(mPAP)of group B was significantly higher than that of group A and mPAP of group C was significantly lower than that of group B(P＜0.01),differences of mean carotid pressure(mCAP) were not significant among three groups (P＞0.05); (2)Electron microscopy and immunohistochemistry showed ligustrazine could inhibit the diposition of collagenous fiber(collagen typeⅠ)in pulmonary arterioles induced by hypoxic hypercapnia; (3) Plasma endothelin level of group C was significantly lower than that of group B (P＜0.01), serum (NO ₂^-/NO₃^-) of group C was significantly higher than that of group B (P＜0.01). CONCLUSION:Ligustrazine can inhibit pulmonary hypertension and the diposition of collagen type Ⅰ in pulmonary arterial wall induced by hypoxic hypercapnia.     

Nitric oxide production,NOS activity and expression in pulmonary arterioles of rats with chronic hypoxic hepercapnic pulmonary hypertension

AIM: To clarify the role of nitric oxide (NO) system in development of chronic hypoxic hypercapnic pulmonary hepertension. METHODS: Male Sprague-Dawley rats were randomly divided into control group and hypoxic hypercapnic group. NO content of plasma was determined, constitutive nitric oxide synthase (cNOS) and inducible nitric oxide synthase (iNOS) were examined using the technique of immunohistochemistry, expression of cNOS mRNA and iNOS mRNA of arteriole were detected by in situ hybridization. RESULTS: Plasma NO concentration, cNOS activity and cNOS mRNA expression in arteriole of chronic hypoxic hypecapnic group were significantly lower than that of control group (P<0.01); activity of iNOS and expression of iNOS mRNA in arteriole showed significantly higher compared with control. CONCLUSION: The disturbance of NO production and NOS expression in arteriole are involved in hypoxic hypercapnic pulmonary hepertension.     

Effect of chronic hypoxia on L-Arginine/nitric oxide pathway in rat pulmonary artery

AIM: To study the effect of chronic hypoxia on L-Arginine/NO pathway in rat pulmonary artery. METHODS: Changes in pulmonary artery L-Arginine(L-Arg) transport, nitric oxide synthase (NOS) activity, plasma nitrite level and L-Arg level in HPH rats were investigated. RESULTS: (1) The mean pulmonary arterial pressure (mPAP) and weight ratio of right ventricle to left ventricle and septum (RV/LV+S) of HPH group were higher than those in control group (P＜0.01). (2) Plasma L-Arg level in HPH group was not significantly changed. (3) At low (0.2 mmol/L)or high(5.0 mmol/L)concentration of L-Arg, the velocity of L-Arg transport in HPH group was lower than that in control group (P＜0.05 or P＜0.01). (4) The activity of pulmonary artery tNOS, iNOS and cNOS in HPH group were increased by 38.0%, 32.8% and 53.0%, respectively (P＜0.01), compared with control group. (5) Plasma NO level of HPH group was decreased, which was negative correlation to mPAP and RV/LV+S (P＜0.01). CONCLUSION: The decrease of nitric oxide generation might result from L-Arg transport injury, while pulmonary artery tNOS, iNOS and cNOS activity were enhanced during chronic hypoxia.     

Effect of diltiazem on pulmonary arterial pressure and ceNOS mRNA expression in pulmonary arteries in chronic hypoxic hypercapnic rats

AIM: To investigate the effect of diltiazem on mean pulmonary arterial pressure (mPAP) and nitric oxide synthase (NOS) in arterioles in chronic hypoxic hypercapnic rats. METHODS: Twenty-four rats were randomly divided into three groups: control group (A), hypoxic hypercapnic group (B), hypoxic hypercapnia+ diltiazem group (C), constitutive endothelial NOS (ceNOS) were observed in arterioles of rats using the technique of immunohistochemistry, ceNOS mRNA were observed by the technique of in situ hybridization. RESULTS: (1) mPAP was significantly higher in rats of B group than that of A and C group(P<0.01). Differences of mCAP were not significant between A group and B groups (P>0.05), but mCAP was lower in rats of C group than that in B group. (2) Light microscopy showed WA/TA (vessel wall area/total area) was significantly lower in rats of C group than that of B group (P<0.01), electron microscopy showed that diltiazem inhibited the proliferation of smooth muscle cells and collageous fibers of pulmonary arterioles in chronic hypoxic hypercapnic rats. (3) Immunohistochemistry showed the average value of integral light density (LD) of ceNOS in pulmonary arterioles was significantly higher in rats of C group than that of B group (P<0.01), in situ hybridization showed LD of ceNOS mRNA in pulmonary arterioles was significantly higher in rats of C group than that of B group (P<0.01). CONCLUSION: Diltiazem inhibited pulmonary hypertension, the proliferation of smooth muscle cells and collagenous fibers of pulmonary arterioles in chronic hypoxic hypercapnic rats by incresing the expression of ceNOS in pulmonary arterioles.     

iNOS-GC-cGMP signaling activation might be involved in vascular hyporeactivity in endotoxemic rats

AIM: To evaluate the activation of inducible nitric oxide synthase (iNOS)-guanylate cyclase(GC)-cyclic guanosine monophosphate(cGMP) signaling on vascular hyporeactivity in endotoxemic rats. METHODS: Twenty-four SD rats were randomly divided into 4 groups as follows: sham operation group (sham group), lipopolysaccharide group(LPS group), LPS+polymyxin B group (LPS+PMX-B group) and polymyxin B group (PMX-B group). Cannulation of the carotid artery was performed to record mean arterial blood pressure (MABP). The levels of plasma NO, iNOS and TNF-α were detected. The tension of the thoracic aortic rings was measured by a biological analytical system. RESULTS: Compared with sham group, MABP in LPS group was significantly lower (P<0.01), whereas MABP in LPS+PMX-B group was significantly higher than that in LPS group (P<0.05), and no statistical difference of MABP between PMX-B group and sham group was observed (P>0.05). The plasma levels of NO and iNOS in LPS group were significantly higher than those in sham group and LPS+PMX-B group (P<0.01). The contraction of isolated thoracic aortic rings stimulated by phenylephrine and the relaxation response by acetylcholine in LPS group were significantly lower than those in sham group (P<0.01), whereas those in LPS+PMX-B group were significantly improved (P<0.01). The vascular hyporeactivity to vasoconstrictors was completely reversed by pretreatment either with aminoguanidine, a selective iNOS inhibitor, or with methylene blue, an inhibitor of NO-sensitive GC. CONCLUSION: The iNOS-GC-cGMP signaling activation might be involved in vascular hyporeactivity in LPS-induced endotoxemic rats. Polymyxin B partly reverses the vascular hyporeactivity to vasoconstrictors by reducing the level of serum TNF-α, which may be mediated by the iNOS-GC-cGMP signal pathways to attenuate the overexpression of iNOS and NO production.     

Immunohistochemical observation and imaging analysis of iNOS and vasoactive intestinal peptide in experimental diabetic rat lung

AIM: The pathological changes in inducible nitric oxide synthase (iNOS) and vasoactive intestinal peptide (VIP) in diabetic rat lung were investigated.METHODS: Using immunohistochemical method and imaging analysis, the changes in iNOS and VIP were observed in normal and diabetic rat lung. RESULTS: In diabetic rats, the iNOS positive or weak positive staining was localized in epithelial cells of bronchi, epithelial cells of alveolar ducts, alveolar sacs, and arteries, but negative in endothelial cells of vein and capillary. Image analysis showed the area, the integral absorbance(IA) and relative contents of iNOS were significant lower than that of control (P＜0.01, P＜0.01 and P＜0.01). In diabetic rats, the ciliated cells of bronchi epithelium showed VIP positive reaction, while the bronchial smooth muscle, surounding tracheobronchial submucosal glands, the tunica adventitia of pulmonary arteries, and alveolar septum were stained weak positive or negative for VIP. Image analysis showed the area, the IA and relative contents of VIP were significantly lower than those of control (P＜0.01, P＜0.01 and P＜0.01).CONCLUSION: The pathological changes in diabetic rat lungs are not only involving autonomic neuropathy but also NANC nerves. Nitric oxide and VIP, which are NANC neurotransmitter, may play an important role in pathogenesis of pathological change in diabetic lung.     

Relationship between expression of heme oxygenase-1 mRNA and pulmonary hypertention induced by hypoxic hypercapnia

AIM: To study the effect of chronic hypoxic hypercapnia on expression of heme oxygenase-1 (HO-1). METHODS: Sprague-Dawley rats were randomly divided into three groups: control group(A),hypoxic hypercapnic group(B), hypoxic hypercapnia+hemin group(C). HO-1 and HO-1 mRNA were observed in pulmonary arterioles by the technique of immunohistochemistry and in situ hybridization. RESULTS: ① mPAP and weight ratio of right ventricle (RV) to left ventricle plus septum (LV+S) were significantly higher in rats of B group than those of A and C group (P<0.01). Differences of mCAP were not significant in three groups(P>0.05). ② Blood CO concentration was significantly higher in rats of B group than that of A group (P<0.01), it was much higher in C group than that of B group(P<0.01). ③ Light microscopy showed that vessel well area/total area (WA/TA), density of medial smooth muscle cell (SMC) and media thickness of pulmonary arterioles were much higher in rats of B group than those of A and C group (P<0.01). ④ The observation by electron microscopy showed proliferation of medial smooth muscle cells and collageous fibers of pulmonary arterioles in rats of B group, hemin could reverse the changes mentioned above. ⑤ HO-1 and HO-1 mRNA in pulmonary arterioles was significantly higher in rats of B group than those of A group(P<0.01), and they were significantly higher in rats of C group than those of B group (P<0.01). CONCLUSION: Expression of HO-1 mRNA and HO-1 in pulmonary arterioles was enhanced by hypoxic hypercapnia. Hemin partly inhibited pulmonary hypertension and pulmonary vessel remodeling by enhancing the expression of HO-1 mRNA and HO-1.     

Correlation between the signal pathway IKK/NF-κB and the anti-oxidant activity in asthma rats and the modulation of Ginkgo biloba extract

AIM:To investigate the correlation between the signal pathway of IKK/NF-κB and the anti-oxidant activity in asthmatic rats and the modulation of Ginkgo biloba extract (Egb). METHODS:Thirty-six male SD rats were randomly divided into three groups:control group (group C), asthmatic group (group A) and Egb group(group E). Asthma in rats was established by ovalbumin (OVA) challenge methods. The mRNA of IKKβ and the protein of NF-κB P65 in lung tissue were assessed by using in situ hybridization with oligonucleotide probe and immunohistochemisty, respectively. RESULTS:The expression of IKKβ mRNA and NF-κB P65 protein in group A were significantly increased when compared with group C (P＜0.01, respectively), but those data in group E were significantly decreased when compared with group A (P＜0.01, respectively). The concentrations of MDA in serum and BLAF in group A were significantly higher than those in control group (P＜0.01，respectively), but the concentrations of MDA in group E were significantly lower than those in group A (P＜0.01, respectively). The concentrations of GSH in group A were significantly lower than those in group C (P＜0.01, respectively), but the concentrations of GSH in group E were significantly higher than those in group A (P＜0.01, respectively). CONCLUSION:The expression of IKKβ mRNA and NF-κB P65 protein were increased significantly in asthmatic rats. This was possibly attributed to the decreased anti-oxidant activity. Egb increased the anti-oxidant activity and inhibited the activity of IKK/NF-κB.     

Renoprotective effects of sesamin on renal hypertensive and hyperlipidemic rats

AIM: To investigate the effects of sesamin on progression of renal injury in renal hypertensive and hyperlipidemic rats (RHHR). METHODS: RHHR was induced by 2K1C and high lipid baitvessel. After 7 weeks of intragastric administration with sesamin, the contents of serum creatinine (Scr), blood urea nitrogen (BUN), 24 h urinary protein excretion (UPE) were measured. In addition, the activity of total antioxidative capacity (T-AOC), superoxide dismutase (SOD), the concentrations of malondialdehyde (MDA), hydrogen peroxide (H2O2), and the nitric oxide synthase (NOS) and nitric oxide (NO) levels in renal homogenate were measured. RESULTS: Compared with the model group, seasamin (in 100 mg·kg-1 and 33 mg·kg-1 groups) evidently decreased the contents of Scr, BUN, UP and the concentration of MDA, iNOS, H2O2 in renal tissure. It also improved the levels of NO, cNOS and activity of SOD, T-AOC in renal tissure. CONCLUSION: Sesamin ameliorates hypertensive and hyperlipidemic-induced renal injury, probably by enhancing antioxidative activity, scavenging hydroxyl radical and restraining iNOS level.     

The protective effect of preconditioning on rabbit liver during ischemia and reperfusion and its potential mechanism

AIM:To investigate the protective effect of preconditioning on rabbit liver during total ischemia and reperfusion and its mechanism. METHODS: Using hepatic ischemia and reperfusion injury (HIRI) model in rabbits, animals were randomly divided into three groups: control group (A), non-preconditioning group(B) and preconditioning group(C), different effects of preconditioning on several parameters including alanine aminotransferase (ALT) activity and levels of nitric oxide (NO) and malondialdehyde (MDA) in plasma or liver tissue as well as hepatocellular morphological changes were measured and observed during HIRI. RESULTS:In C group NO levels of plasma and liver tissue were higher than those in B group (P＜0.05);While MDA levels and ALT value in plasma were lower than those in B group (P＜0.05 and P＜0.01); and there were not significant differences between C and A group (P＞0.05); abnormal morphological chages of liver cells in A group were ameliorated remarkably too during HIRI. CONCLUSION:Preconditioning can attenuate HIRI by improving NO level and reducing oxygen free radicals level.     

The kinetic alteration of nitric oxide formation in the lungs in the development of pulmonary fibrosis of rats

AIM: To observe the kinetic alteration of nitric oxide formation in the lungs in the development of pulmonary fibrosis in the rat. METHODS: The contents of hydroxyproline in the lungs, NO₂^-/NO₃^- (nitrite/nitrate) in out-flowing and in-flowing pulmonary blood (OPB, IPB) were assayed on the day 7, 14, 21, 30 and 70 after intratracheal administration of bleomycin A₅ . The content of NO₂^-/NO₃^- in supernatants of culture of the alveolar macrophages (AMs) and the amount of iNOS positive stain cells in lung tissue section were also observed in the rat on 14th day after-bleomycin A₅ administration. RESULTS: The content of lung hydroxyproline had no change on the 7th day, increased on the 14th day (P＜0.05), increased significantly on the 21th day, 30th day and 70th day post-bleomycin A₅ compared with control rats. On the 7th day and 14th day, the content of NO^- ₂ /NO₃^- increased in OPB and decreased in IPB (P＜0.01). On the 21th day, the content of NO₂^-/NO₃^- abated in OPB (P＞0.05) but still decreased in IPB (P＜0.01). On the 30th day and the 70th day, the NO₂^-/NO₃^- level recovered both in OPB and IPB. AMs from rats on the 14th day post-bleomycin A₅ showed significant elevation (P＜0.01) in NO₂^-/NO₃^- level. The amount of iNOS positive stain cells increased in rats on the 14th day post-bleomycin A₅. CONCLUSION: The amount of NO in the lungs was high in the initial phase of fibroproliferative reaction induced by bleomycin A₅ ,and these might be associated with the enhanced ability of AMs to release NO and the increased amount of iNOS.     

Influence of transection of the cervical sympathetic trunk on content of NO and expression of NOS in placenta of rats with pregnancy-induced hypertension syndrome

AIM:To observe the influence of transection of the cervical sympathetic track (TCST) on the content of NO and the expression of eNOS mRNA and iNOS mRNA in placenta of the rats with pregnancy-induced hypertension syndrome (PIH).METHODS: Pregnant Wistar rats were randomly divided into 5 groups: control group (C): saline was injected subcutaneously from 14th day to 20th day of gestation;PIH group 1 (H1) and group 2 (H2): L-NAME was respectively injected with 125 mg/kg and 62.5 mg/kg,respectively,then the other procedures were the same as group C;Operation group (O): TCST was operated on 14th day of the gestation,then the other procedures were the same as group H1;sham operation group (S): the cervical sympathetic trunk was only separated and exposed on 14th day of the gestation,then the other procedures were the same as group H1.RESULTS: (1) Except the base value of the BP and protein in urine of the pregnant rats,all the parameters observed in group H1 and H2 were higher than those in group C significantly (P<0.01),and in group H2 were lower than those in group B1 markedly (P<0.01).(2) In comparison with those in group C,the size and body weigh of fetus in group H1,H2 decreased markedly (P<0.01).The above indexes in group H1 were lower than those in group H2 markedly (P<0.01,P<0.05).The changes of the rate of embryo absorption and fetal death,and deformity rate of the fetal rats were contrary to the above indexes.(3) The content of NO and the expression of eNOS mRNA and iNOS mRNA in placenta in group H1 and H2 were lower than those in group C markedly (P<0.01).Those in group H1 were lower than those in group H2 obviously (P<0.01,P<0.05).Those in group O were higher than those in group H1 markedly (P<0.01).CONCLUSION: TCST protects pregnant rats against PIH,and it was related to the mRNA expression of eNOS and iNOS and the content of NO in placenta tissue.     

Effect of mesenteric lymph duct ligation on actue lung injury in rats

AIM：To explore the effect of mesenteric lymph duct ligation against actue lung injury (ALI) in rats.METHODS：45 Wistar rats were divided into three groups：the ligation group,the non-ligation group and sham operated group,and the two-hit model was established by hemorrhage and LPS injection.Mesenteric lymph was diverted by ligating mesenteric lymph duct in ligation group.All rats facilitated blood withdrawal for blood sample to arterial gas analysis after 24 hours.Then the WBC,NO,NOS,MDA,SOD and lung permeability index (LPI) were determined in bronchoalveolar lavage fluid (BALF),the MPO and ATPase activity were determined in lung homogenate.The ultrastructure was also observed.RESULTS：After two-hit,the PaCO2,the total cells and PMN,the NO2-/NO3-,NOS and MDA content in BALF and MPO activity in lung homogenate and LPI in non-ligation group were significantly increased than those in sham operated group.PaO2 and pH in arterial blood,SOD in BALF and the ATPase in lung homogenate were significantly lower (P<0.01 or P<0.05).The total cells and PMN,MDA,NO2-/NO3- in BALF,LPI in ligation group were significantly increased than those in sham operated group,and SOD in BALF was significantly lower (P<0.01 or P<0.05).The pH and PaO2 in arterial blood,the ATPase in lung homogenate in ligation group were significantly increased than those in non-ligation group,and the PaCO2,the total cells,PMN,NO2-/NO3-,NOS,MDA in BALF,LPI,and MPO in lung homogenate in ligation group were significantly lower than those in non-ligation group (P<0.01 or P<0.05).The injury of pulmonary vascular endothelium in ligation group was lighter than that in non-ligation group.CONCLUSION：The ligation of mesenteric lymph duct attenuates the ALI of rats.Mesenteric lymph might play an important role in the pathogenesis of ALI.     

Effects of external counterpulsation on nitric oxide system in myocardial infarction canines

AIM:To investigate the effects of external counterpulsation(ECP)on nitric oxide(NO)and nitric oxide synthase(NOS)and the expression of NOS gene in myocardial infarction canines.METHODS:Nineteen healthy dogs were randomly divided into three groups ie.controls, ischemia group, ischemia and ECP group.Serum NO concentrations and myocardium NO levels and NOS specific activity were determined by modified nitrate reductase method.T he protein synthesis of sub-type NOS including inducible NOS(iNOS)and endothelial NOS(eNOS)of myocardial tissue were also determined by immunohistochemical method.The constitutive NOS(cNOS)mRNA was measured via in situ hybridization.RESULTS:120 and 180 minutes after the ligat ing of LAD, serum NO concentration in ECP groups were higher than those in ischemic groups(P<0.05).The NO levels and NOS specific activity in myocardium of ischemic dogs were lower than those in controls and ECP group(P<0.05).Protein synthesis of iNOS increased and that of eNOS decreased in ischemic myocardium.But ECP could control the protein synthesis of iNOS, and increase that of eNOS.Further studies showed that the expression of cNOS mRNA decreased in ischemic myocardial tissue, ECP might promote the expression of it and regulate NOS in the gene level.CONCLUSION:The results suggested that it was one of the most important mechanisms through raising the NO levels to protect ischemic myocardium in ECP.     

Role of prostaglandins,nitric oxide and potassium channel in the blunting of hypoxic pulmonary vasoconstriction in the high altitude adaptive animal

AIM: To investigate the possible role of prostaglandin, NO and potassium channel in the adaptive blunting of hypoxic pulmonary vasoconstriction (HPV) in high altitude animal (pika). METHODS: The effect of L-NAME, indomethacin and 4-AP on the response of isolated lung strips of pika and Wistar rats instead of pulmonary artery to acute hypoxia were studied. RESULTS: (1) After inhibition of prostaglandins by indomethacin, the percentage increase in hypoxic constriction in lung tissue strip of pikas was greater than that in Wistar rats , P＜0.05; (2) After inhibition of NO synthesis by L-NAME, the percentage increase in hypoxic constriction in lung tissue strip of pikas was greater than that in Wistar rats , P＜0.05; (3) After administration of 4-AP, there was no significant difference in the percentage decrease in hypoxic constriction of lung tissue strip between pika and Wistar rat. CONCLUSIONS: (1) Prostaglandins and NO might modulate HPV in either rat of pika; the closure of Voltage-gated K⁺ channels might mediate HPV in either rat or pika. (2) Prostaglandins and NO might play an important role in the blunting of HPV in pika, Voltage-gated K⁺ channels may play a minor role in the blunting of hypoxic pulmonary vasoconstriction in pika.     

Protective effects of total saponins of panax notoginseng on myocardial hypertrophy and fibrosis induced by isoproterenol in rats

AIM: To investigate the protective effects of total saponins of panax notoginseng (PNS) on myocardial hypertrophy and fibrosis induced by isoproterenol (ISO) in rats.METHODS: Myocardial hypertrophy and fibrosis model of rats were induced by injection of ISO (5 mg·kg^-1·d^-1,sc) for 7 days.From day 2,the rats were administered with PNS at dose of 25 and 50 mg·kg^-1·d^-1,ip for 14 days,the control and ISO model group were received saline injection.Then,the heart-weight (HW),left ventricular weight (LVW),the ratio of HW/BW and LVW/BW (LVI) were measured;the hydroxyproline and malondialdehyde (MDA) and angiotensin (AngII) content of left ventricle.The level of nitric oxide (NO),nitric oxide synthase (NOS),superoxide disrnutase (SOD) and glutathione peroxidase (GSH-Px) activities in left ventricle were determined by spectrophotemetry and radioimmunoassay,respectively.RESULTS: Compared with NS control group,the ratio of HW/BW,LVW/BW and the content of hydroxyproline,AngII,MDA and iNOS activity in the left ventricle were significantly increased.The cNOS,SOD,GSH-Px activities and NO content were obriously decreased in the ISO model group.After treatment with PNS,the left ventricular NO content,cNOS,SOD and GSH-Px activities were markedly higher than those in ISO model group.The content of MDA,AngII and iNOS activities and the ratio of HW/BW,LVI were significantly lower than those in ISO model group.CONCLUSION: PNS reverses the myocardial hypertrophy and fibrosis induced by isoproterenol in rats.This effect may be related to eliminating the oxygen free radicals and raising NO level.     

Phenytoin inhibited changes in nitric oxide of rat hippocampus induced by stress

AIM: To investigate the changes in nNOS and iNOS expression of hippocampal CA3 pyramidal neurons and NO₂^-/NO₃^- level of hippocampal homogenate of rats induced by stress, and to explore the effect of phenytoin on them. METHODS: Rats were subjected to forced-swimming stress, phenytoin was administered(ip) at 30 min before stress. Using the immunohistochemistry and the computerized image technique, the expression levels of nNOS and iNOS of rat hippocampal CA3 pyramidal neurons were assayed quantitatively, and the NO₂^-/NO₃^- level of hippocampal homogenate was also measured using nitric acid deoxidize enzyme method. RESULTS: The nNOS average grey degree of hippocampal CA3 pyramidal neurons was significantly lower in stress group (155.42±3.77)than that in control group(164.54±4.62)and in stress plus phenytoin group(164.27±2.55)(P<0.01); The iNOS relative sectional area proportion of hippocampal CA3 pyramidal neuron was significantly larger in stress group(5.87%±2.90%) than that in control group (0.90％±0.89%) and in strers plus phenytoin groups (0.90%±0.88%)(P<0.01); The NO₂^-/NO₃^- level of hippocampal homogenate was significantly higher in stress group(42.75 umol/L±14.49 umol/L)than that in control group(21.23 umol/L±6.99 umol/L)and in stress plus phenytoin group(18.40 umol/L±8.11 umol/L)(P<0.01). CONCLUSION: It is suggested that the stress could induce nNOS and iNOS expression in CA3 pyramidal neurons and excessive production of NO in hippocampus of rats, which could be inhibited by phenytoin.