Antioxidative Propolis From Stingless Bees (Heterotrigona Itama) Preserves Endothelium-Dependent Aortic Relaxation of Diabetic Rats: The Role of Nitric Oxide and Cyclic Guanosine Monophosphate

Propolis from stingless bees (Heterotrigona itama) is a resinous compound that exhibits antihyperglycaemia, free radical scavenging, and cardioprotective properties. The effect of propolis on diabetic vessels has not been investigated. Thus, this research aimed to determine the effect of propolis supplementation on the level of antioxidants and its mechanism of action in the aorta of diabetic rats. Male Sprague-Dawley rats were divided into five groups (n=8/group): healthy (control), untreated diabetes (DM), metformin-treated diabetes (DM+M, 300 mg/kg/day metformin), propolis-treated diabetes (DM+P, 300 mg/kg/day propolis extract) and diabetes with combined treatment (DM+M+P, dosage as former). Oral supplementation was conducted for four weeks immediately upon successful induction of diabetes by streptozotocin (60 mg/kg, intraperitoneal injection). At the end of the study, the rats were euthanised, and thoracic aorta was processed into tissue homogenates to determine the levels of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase-1 (GPx-1) and soluble receptor for advanced glycation end-products (sRAGE). Aorta segments were harvested to examine their relaxation response towards graded concentration of acetylcholine (Ach; 10-8-10-4) M following precontraction with phenylephrine (PE; 10-6 M). Vasorelaxation towards a cumulative dose of propolis (0.01-1.00%) using PE-precontracted healthy aorta (n=6/experiments) was investigated under various simulated conditions: physiological buffer, L-NAME (10-4 M), methylene blue (10-5 M), indomethacin (10-5 M) and elevated glucose (25 mM). Propolis maintained antioxidative enzymes and sRAGE decoy molecules in the aortic tissue of the diabetic rats. The amelioration of diabetes-induced impairment of endothelium-dependent relaxation by propolis was mediated through the nitric oxide(NO)-cyclic guanosine monophosphate (cGMP) pathway. This non-clinical study reports vasoprotective property of propolis in diabetes mellitus.

Inhibition Effect of TLR4mAb on mmLDL Impaired Endothelium-dependent Vasodilatation in Mouse Mesenteric Artery / 中国药学杂志

OBJECTIVE: To investigate the effect and mechanism of TLR4 monoclonal antibody (TLR4mAb) on mmLDL induced impairment of endothelium-dependent vasodilatation in mouse mesenteric artery. METHODS: The experiment established three groups of normal saline group, mmLDL treatment group and TLR4mAb intervention group. The concentration of IL-1β and TNF-α in plasma was determined by enzyme-linked immunosorbent assay (ELISA). Measurement of endothelium-dependent vasodilatation was achieved by microvascular tension mapping. Western blot and RT-PCR were used to investigate the expression level of protein and mRNA expressions in vascular tissues. In addition, ultra-structure of mesenteric artery endothelial cells was observed by transmission electron microscope. RESULTS: TLR4mAb could improve the damage of mmLDL induced impairment of endothelium-dependent vasodilatation in a dose-dependent manner. Besides, TLR4mAb obviously up-regulated protein expressions in KCa3.1-channel and KCa2.3-channel, and down-regulated the expression of inflammatory factors TNF-α and IL-1β. Furthermore, the improvement of mmLDL impaired vascular endothelial cells and endothelium-dependent vasodilatation might be correlated with its competitive antagonism of mmLDL-activated TLR4 signal transduction pathway and its downstream NF-κBp65 and p-38 MAPK pathway. CONCLUSION: Administration of TLR4mAb in advance can alleviate the impairment of endothelial cells and the decrease of endothelium-dependent vasodilatation induced by mmLDL, and inhibit the overexpression of inflammatory factors. Regulation of TLR4 pathway as well as its downstream NF-κBp65 and P-38 MAPK pathways may be effective targets for the prevention and treatment of cardiovascular diseases.

Potentiation of endothelium-dependent vasorelaxation of mesenteric arteries from spontaneously hypertensive rats by gemigliptin, a dipeptidyl peptidase-4 inhibitor class of anti-diabetic drug

Dipeptidyl peptidase4 (DPP4) inhibitors such as gemigliptin are anti-diabetic drugs elevating plasma concentration of incretins such as GLP-1. In addition to the DPP4 inhibition, gemigliptin might directly improve the functions of vessels under pathological conditions. To test this hypothesis, we investigated whether the acetylcholine-induced endothelium dependent relaxation (ACh-EDR) of mesenteric arteries (MA) are altered by gemigliptin pretreatment in Spontaneous Hypertensive Rats (SHR) and in Wistar-Kyoto rats (WKY) under hyperglycemia-like conditions (HG; 2 hr incubation with 50 mM glucose). ACh-EDR of WKY was reduced by the HG condition, which was significantly recovered by 1 µM gemigliptin while not by saxagliptin and sitagliptin up to 10 µM. The ACh-EDR of SHR MA was also improved by 1 µM gemigliptin while similar recovery was observed with higher concentration (10 µM) of saxagliptin and sitagliptin. The facilitation of ACh-EDR by gemigliptin in SHR was not observed under pretreatment with NOS inhibitor, L-NAME. In the endotheliumdenuded MA of SHR, sodium nitroprusside induced dose-dependent relaxation was not affected by gemigliptin. The ACh-EDR in WKY was decreased by treatment with 30 µM pyrogallol, a superoxide generator, which was not prevented by gemigliptin. Exendin-4, a GLP-1 analogue, could not enhance the ACh-EDR in SHR MA. The present results of ex vivo study suggest that gemigliptin enhances the NOS-mediated EDR of the HG-treated MA as well as the MA from SHR via GLP-1 receptor independent mechanism.

Protection of puerarin on impaired vascular endothelial function induced by glycosylated protein / 中国药学杂志

OBJECTIVE: To investigate the effects of puerarin on impaired endothelium-dependent relaxation induced by glycosylated bovine serum albumin (GBSA) in rabbit thoracic aorta and its mechanisms. METHODS: The rings were incubated with GBSA for 30 min to induce endothelial dysfunction, and with puerarin(0.25, 0.5 and 1 g · L-1), A-nitro-L-arginine methyl ester (L-NAME, 30 νmol · L-1), and indomethacin(10 μmol · L-1) to investigate the protective effect of puerarin on impaired vascular endothelial function elicited by GBSA, and the effect of L-NAME and indomethacin on the protective effect of puerarin. Moreover, the content of nitric oxide (NO) and malonaldehyde (MDA) and the activity of superoxide dismutase(SOD) in the rings were measured. RESULTS: Exposure of aortic rings to GBSA (200 mg · L-1) for 30 min resulted in a significant inhibition of endothelium-dependent relaxation, but had no affect on endothelium-independent relaxation. GBSA significantly decreased the level of NO and the activity of SOD but hugely increased the content of MDA in vascular tissues. Pre-incubation of aortic rings with puerarin markedly attenuated the inhibition of endothelium-dependent relaxation induced by GBSA. This protective effect of puerarin (1 g · L-1) was partially inhibited by L-NAME but not by indomethacin. Puerarin obviously increased NO level and SOD activity but evidently decreased MDA content in rings. CONCLUSION: Puerarin can protect against vascular endothelial dysfunction caused by GBSA and its mechanisms may be related to enhancing NO synthesis and its anti-oxidation.

Psychological stress reduces the plasma NO level and NO-regulating protein expression in the vascular en-dothelial cells of rats / 医学研究生学报

[Abstract ] Objective The mechanism of psychological stressi-nduced damage to vascular endothelial cells (VEC) is not yet clear.This study was to investigate the impact of psychological stress on the NO level and NO-related regulatory protein expression in the plasma of rat models of psychological stress-induced VEC injury. Methods Twenty male SD rats were equally randomized into a con-trol group and a model group, the former raised together, with water regularly fed at 9:00 and 21:00 hours for 10 minutes a day, while the latter raised alone, with water regularly fed at the same hours for 10 minutes a day for the first 7 days and then with water or an empty bottle at the same hours for 10 minutes a day according to the random table.Ninety days later,all the rats were intraperitoneally injected with normal saline at 0.2 ml per 100 g body weight twice a day.Then the behaviors of the animals were observed by open field tests, the contents of cortisol (COR),adrenaline (Adr), and endothelin-1 (ET-1) in the plasma measured by ELISA, the NO level detected by the nitrate reductase method, and the expression of NO-related regulatory proteins in VECs determined by LC-ESI-MS. Results Com-pared with the control group, the model rats showed significant increases in the vertical score (7.00 ±0.70 vs 11.28 ±1.79), horizontal score (37.60 ±4.500 vs 56.25 ±1.71), and total score (44.50 ±5.50 vs 67.25 ±2.98) (P<0.01) as well as in the levels of COR ([65.28 ±2.21] vs [83.85 ±1.95] ng/mL ) and Adr ([3.85 ±0.35] vs [15.14 ±3.97] pg/mL) (P<0.01), but a remarkable de-with vacuoles in the VECs in the model group and structural integrity, ridge clarity, and tight pack in the VEC mitochondria in the con-trol. Conclusion Psychological stress induced by empty bottle stimulation can reduce the NO level and the expression of NO-related regulatory proteins in the plasma, which may cause both functional and structural damages to VECs.

Prevention of endothelial dysfunction in streptozotocin-induced diabetic rats by Sargassum echinocarpum extract.

Aim This study aimed to elicit the protective effect of Sargassum echinocarpum extract on endothelial dysfunction in thoracic aorta of streptozotocin-induced diabetic rats. Methods The animals were divided into 5 groups. The first was normal, the second was diabetic non treated animals. The third to fifth groups were the diabetic animals which given Sargassum echinocarpum extract (150; 300, and 450 mg kg-1 body weight, respectively) by oral gavage and extract treatment was given for 12 weeks. Diabetes was induced by single administration of streptozotocin (45 mg kg-1, i.p.), dissolved in freshly prepared 0.1 M citrate buffer, pH 4.5. Diabetes was confirmed ten days latter in streptozotocin induced animals showing blood glucose levels > 200 mg dL-1 (11.1 mmol L-1) as monitored in the blood from tail vein using glucometer. After the treatment period, the blood serum acquired was used for antioxidant enzymes assays and the thoracic aorta was used for vasorelaxation assay. Results There was a significant decrease in the activity of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-px) in diabetic rats (3.31+ 0.12;67.17 + 0.62;35.10 + 0.83) comaped to control rats (9.97 + 0.12;185.31 + 0.23;116.38 + 0.88). Administration of Sargassum extract increased the activity of SOD, CAT, and GSH-px. The diabetic rats exhibit endothelial dysfunction as shown by loss of vasodilatory response to acethylcholine (ACH). This was restored by administration of Sargassum extract. Conclusion Sargassum echinocarpum extract ameliorates oxidative stress and reverses the endothelial dysfunction associated with diabetes. This effect appears to be due to its antioxidant properties.

Factors associated with Endothelial Dysfunction in Hemodialysis Patients / 대한신장학회지

PURPOSE: Endothelial dysfunction is an event in the atherosclerotic process usually considered reversible at its early stage. Early detection, therefor, may improve the prognosis in the cardiovascular disease. The aim of this study was to investigate the vascular function in hemodialysis (HD) patients and to explore its relation to other various parameters with a specific emphasis on systemic inflammatory reaction (SIR), nutritional status and the presence of ischemic heart disease (IHD). METHODS: Flow-mediated endothelium-dependent vasodilatation (FMD) was measured, using Doppler sonogram, in 37 stable HD patients, 11 healthy people and 24 hypertensive controls. Nitroglycerine- induced endothelium-independent vasodilatation (EIV) and peak reaction time (PT) of each FMD and EIV were also measured. RESULTS: FMD in HD patients was decreased compared to healthy group whereas it was comparable in HD patients and hypertensive control. EIV in HD patients was significantly decreased compared to healthy and hypertensive controls. PT of each FMD and EIV was significantly delayed in HD patients. Each FMD and EIV showed a negative correlation with serum hsCRP level, but no significant correlations of FMD with other parameters were noted. Both FMD and EIV were further decreased in HD patients with IHD than non-IHD group. CONCLUSION: Our study confirmed a characteristic pattern of vascular dysfunction in HD patients: the impaired endothelial and smooth muscle function with a delayed reaction time. Importantly, SIR was one of the important factors determining vascular dysfunction in HD patients. Further studies will be necessary to define the causative role of SIR on endothelial dysfunction and the effect of inflammation- modulating therapy.

Protective Effect of Captopril on Nicotine-induced Endothelial Dysfunction in Rats / 中国药房

OBJECTIVE: To discuss the protective effect of captopril on the nicotine-induced impairment of endothelium-dependent relaxation(EDR) in rat mesenteric arteries and explore the possible mechanisms underlying the observed protective effects of captopril.METHODS: A total of 30 rats were randomly divided into 3 groups: normal control group,nicotine group(2 mg?kg-1),captopril group(nicotine 2 mg?kg-1+captopril 3 mg?kg-1).After treatment for 4 weeks,vasodilatation rate of mesenteric arteries,the content of NO and NOS,and the SOD activities in serum were measured.RESULTS: Nicotine significantly decreased the vasodilatation rate of mesenteric arteries and decreased the content of NO and NOS,SOD activities in serum(P

Effect of oxidized low-density lipoprotein on endothelium-dependent relaxation in hyperlipidemic patients / 吉林大学学报(医学版)

Objective To study the effecet of oxidized low-density lipoprotein(Ox-LDL) on endothelium-dependent relaxation and mechanism of susceptibility to atherosclerosis(AS) in hyperlipdemic male patients.(Methods)LDL isolated from 13 normal patients and 29 hyperlipidemic patients were modified by CuSO_4.The amount of malondialdehyde(MDA) was measured by TBARS.The amount of lysophosphatidylcholine(LPC) was determined by the Bartlett.Endothelium-dependent relaxation was produced by acetylcholine.Results After LDL from normal and hyperlipidemic patients were modified by CuSO_4,the amount of MDA was increased(P

Prevention of aminoguanidine against impairment of endothelium-dependent relaxation induced by glycosylated proteins in isolated rat aorta / 中国药理学通报

AIM This study was designed to investigate the effect of aminoguanidine, an inhibitor of the glycosylated proteins formation, on the impairment of endothelium dependent relaxation induced by advanced glycation end products (AGE) in isolated rat thoracic aorta and its possible mechanisms. METHODS Exogenous glycosylated bovine serum albumin (AGE BSA) was prepared. Aortic rings were exposed to AGE BSA for 60 min to induce the impairment of endothelium dependent vasodilatation. In the drug treated groups, aortic rings were incubated with drug for 15 min and then exposed to AGE BSA for another 60 min in the presence of the drug. Vasodilator responses to acetylcholine (ACh) or sodium nitroprusside (SNP) of aortic rings were measured by isometric tension recording after drug treatment. RESULTS AGE BSA significantly inhibited the endothelium dependent relaxation in response to ACh, but did not affect endothelium independent relaxation in response to SNP. Pre incubation of aortic rings with aminoguanidine(50～500 ?mol?L -1 ) for 15 min and co incubation of aortic rings with AGE BSA for another 60 min markedly attenuated the inhibition of endothelium dependenet relaxation induced by AGE BSA in a dose dependent manner. Superoxide diamutase (SOD, 2?10 5 U?L -1 ), a scavenger of superoxide anions, also prevented the inhibition of endothelium dependent relaxation, which is similar to the effect of 500 ?mol?L -1 aminoguanidine. Furthermore, aminoguanidine (500 ?mol?L -1 ) also reversed impairment of endothelium dependent relaxation of rat aortic ring induced by endogenous oxygen free radicals generated by diethyldithiocarbamate (DETC, 10 ?mol?L -1 ) via inhibiting intracellular SOD. CONCLUSION Aminoguanidine can protect rat aortic endothelium against damage due to AGE BSA, and the beneficial effect of aminoguanidine may relate to its antioxidant properties.

Effects of perfusion pressure with cold cardioplegic solution on porcine coronary arterial endothelial and smooth muscle function / 第三军医大学学报

Objective To investigate the effects of perfusion pressure with a cardioplegic solution on endothelium-dependent relaxation and smooth muscle function of porcine coronary artery. Methods The hearts were infused with a modified St.Thomas’ hospital solution at the pressures of 40, 60 and 80 mmHg. The distal part of porcine left anterior descending coronary artery (LAD) having a diameter of 1.0-1.5 mm, was dissected free from the surrounding tissue, cut into 1 mm long segments, immediately transferred to organ baths for the evaluation of endothelial and smooth muscle function. Results Smooth muscle function was not affected after cardioplegic flushing at the pressures used in this study. The maximal endothelium-dependent relaxations of the vessels in 40 and 60 mmHg groups were not reduced compared to fresh segments . The maximal EDR was significantly reduced to (90.8?2.2)% (P

Effects of Thiopental Sodium, Midazolam, Propofol and Ketamine on Endothelial Nitric Oxide in Rat Thoracic Aortic Rings / 대한마취과학회지

BACKGROUND: Compared to inhalation and local anesthetics, little is known about the mechanisms of vascular effects of intravenous anesthetics. So we studied the effects of thiopental sodium, midazolam, propofol and ketamine on the endothelial nitric oxide-cGMP pathway and also on the membrane cyclooxygenase pathway. METHODS: After isolating ring strips of rat thoracic aorta, we measured the relaxation ED50 values of the four intravenous anesthetics from the maximally contracted using phenylephrine 10(-5)M. Then using L-NAME and methylene blue, we studied the effects of the drugs upon the NO-cGMP system. In addition, another pathway of vasodilation through membrane prostaglandin metabolism was examined using the membrane cyclooxygenase inhibitor, indomethacine. RESULTS: The following results were obtained. 1. Thiopental sodium (10(-5)M) did not have any effect on the PE induced contractions of aortic rings but midazolam (10(-6)M), propofol (10(-4)M) and ketamine (10(-3)M) significantly (P < 0.05) inhibited the PE induced contractions of aortic rings. 2. Midazolam 10(-6)M and propofol 10(-4)M induced relaxation of aortic rings were recovered with L-NAME pretreatment but ketamine induced relaxation was not recovered with L-NAME. 3. Midazolam 10(-6)M induced relaxation was not recovered with methylene blue pretreatment, but propofol 10(-4)M induced relaxation was recovered with methylene blue. 4. Indomethacine pretreatment induced further relaxation of midazolam or propofol induced relaxation of aortic rings. CONCLUSIONS: Midazolam, propofol and ketamine, but not thiopental sodium, relax rat thoracic aortic rings, and these relaxation effects of midazolam and propofol are endothelium dependent. Cyclooxygenase inhibition is related at least in part to midazolam or propofol induced relaxation, and guanylate cyclase to propofol induced relaxation.

The Effect of Pravastatin on Impaired Endothelium-dependent Relaxation of Isolated Rabbit Aortic Rings Induced by Homocysteine / 中国医师杂志

Objective To explore whether pravastatin protects endothelium against the damage induced by homocysteine (Hcy) in isolated rabbit aorta. Methods Endothelium-dependent relaxation responses to acetylcholine (ACh) of thoracic aortic rings were measured by isometric tension recording before and after aortic rings exposed to Hcy in the absence or presence of pravastatin (PT) to estimate the injury effect of Hcy and the protective effect of pravatatin on rabbit aortic endothelium, respectively. Results Incubation of aortic rings with 1～10mmol/L Hcy for 30min significantly inhibited endothelium-dependent relaxation response to ACh of aortic rings in a concentration-dependent manner. Pre-incubation of aortic rings with 0.3～3mmol/L PT for 15min and co-incubation of aortic rings with 3mmol/L Hcy for another 30min markedly attenuated the inhibition of endothelium-dependent relaxation induced by Hcy in a concentration-dependent manner. Conclusion Pravastatin can improve the impairment of endothelium-dependent relaxation induced by Hcy in isolated rabbit aorta.

Estrogen affects vascular tone differently according to vasoactive substances in ovariectomized Sprague-Dawley rat

The favorable effects of estrogen on cardiovascular diseases can be explained by several mechanisms such as changes in serum lipid profiles and thrombogenecity. Estrogen also affects the vascular tone, but there has been no report in which the effect of estrogen was tested comprehensively for several vasoactive substances, especially after long-term administration. Two weeks after bilateral ovariectomy in 8-week old female Sprague-Dawley rats, placebo or 17 beta-estradiol (E2) pellets (0.5 mg; released over 3 weeks) were implanted subcutaneously. Two weeks after pellet implantation, organ chamber experiments were performed using aortae. Compared with control, E2-treated vessels showed impaired endothelium-dependent relaxation to acetylcholine. E2 enhanced the contraction to norepinephrine and U46619 and had no effect on endothelin-1-induced contraction. In contrast, the contraction to angiotensin (AT)-II was inhibited by E2. Northern blot analysis for AT1 receptor expression using cultured aortic smooth muscle cells showed no difference between control and E2-treated cells, suggesting that AT1 receptor downregulation is not the likely mechanism. These results suggest that E2 affects the vascular tone variably according to vasoactive substances.

Effect of Estrogen Replacement on Vascular Responsiveness in Ovariectomized Spontaneously Hypertensive Rat

BACKGROUND: Although postmenopausal estrogen replacement therapy is known to reduce cardiovascular mortality, the mechanism is not clear yet. Furthermore, the effect of estrogen on vascular tonus is reportedly variable according to the animal models, vascular beds and agonists used. MATERIALS AND METHOD: Bilateral ovariectomies were performed in 12 week-old, 18 spontaneously hypertensive rats (SHR) and 18 normotensive Wistar-Kyoto rats (WKY). Rats were divided into three groups according to the dose of 17beta-estradiol (E 2 ) pellets implanted subcutaneously two weeks after ovariectomy: control (no implantation), low-dose (0.5 mg) and high-dose (5 mg) E 2 replacement group. Two weeks after pellet implantation, organ bath experiments were performed using descending thoracic aortae. For endothelium-dependent relaxation, acetylcholine (10(-9) -3x10(-6) M) was cumulatively added into the vessels precontracted with 10(-7) M norepinephrine (NE). For vasoconstrictor responses, cumulative concentration-contraction curves were constructed in quiescent vessels using NE (10(-9) -10(-5) M), U46619 (10(-9) -3x10(-6) M), endothelin-1 (10(-10) -10(-7) M). In addition, contraction to angiotensin II (10(-7) M) was also obtained. Serum 17beta-estradiol levels were measured by radioimmunoassay. Blood pressure was measured by tail-cuff method in some SHRs before ovariectomy and after placebo/E 2 replacement. RESULTS: Endothelium-dependent relaxation to acetylcholine was impaired in WKY treated with 5 mg E 2 (pIC 50 : control vs 5mg E 2 : 7.75+/-0.13 vs 7.27+/-0.16: n=6: p<0.05). No significant effect was noted in SHR. Contraction to angiotensin II was inhibited by low-dose E 2 in WKY and high-dose E 2 in SHR (% of the contraction to 60 mM KCl: WKY: control vs 0.5 mg E 2 : 39+/-5 vs 25+/-2: SHR: control vs 5 mg E 2 : 34+/-4 vs 22+/-2: n=6 and p<0.05 in WKY and SHR). In contrast, NE-induced contraction was enhanced by E 2 replacement (both low- and high-dose) in WKY and SHR (WKY: control vs 0.5 mg E 2 vs 5 mg E 2 : AUC: 280+/-24 vs 387+/-26 vs 374+/-25: maximal contraction: 137+/-8 vs 166+/-8 vs 162+/-3: pD 2 : 7.63+/-0.11 vs 8.17+/-0.13 vs 8.13+/-0.13: SHR: control vs 0.5 mg E 2 vs 5 mg E 2 : AUC: 265+/-17 vs 349+/-16 vs 406+/-19: maximal contraction: 152+/-6 vs 181+/-9 vs 203+/-16: pD 2 : 7.45+/-0.13 vs 7.91+/-0.08 vs 8.04+/-0.04: n=6 and p<0.05 between control and treated groups in WKY and SHR for all parameters). Contraction to U46619 was enhanced by E 2 replacement in SHR (control vs 0.5 mg E 2 : AUC: 478+/-30 vs 574+/-23: maximal contraction: 181+/-9 vs 230+/-10: n=6: p<0.05 for both parameters). Maximal contractile response to endothelin-1 was also enhanced in SHR (control vs 0.5 mg E 2 vs 5 mg E 2 : maximal contraction: 165+/-7 vs 189+/-7 vs 199+/-8: n=6 and p<0.05 between control and treated groups) but not in WKY. Blood pressure was not different between placebo and E 2- treated SHR (171+/-2 vs 174+/-4 mmHg). CONCLUSION: In WKY, chronic high-dose estrogen replacement impairs endothelium-dependent relaxation to acetylcholine.: low-dose estrogen replacement does not affect endothelium-dependent relaxation in SHR and WKY. Estrogen replacement enhances the contraction to most of the contractile agonists tested except angiotensin II in both WKY and SHR. These results suggest that estrogen replacement affect the vascular tonus differently according to the vasoactive substances and/or hormones without significant effect on blood pressure.

The involvement of K+ channels and the possible pathway of EDHF in the rabbit femoral artery

Experiments were designed to characterize the cellular mechanisms of action of endothelium-derived vasodilator substances in the rabbit femoral artery. Acetylcholine (ACh, 10(-8)-10(-5) M) induced a concentration-dependent relaxation of isolated endothelium-intact arterial rings precontracted with norepinephrine (NE, 10(-6) M). The ACh-induced response was abolished by the removal of endothelium. NG-nitro-L-arginine (L-NAME, 10(-4) M), an inhibitor of NO synthase, partially inhibited ACh-induced endothelium-dependent relaxation, whereas indomethacin (10(-5) M) showed no effect on ACh-induced relaxation. 25 mM KCl partially inhibited ACh-induced relaxation by shifting the concentration-response curve and abolished the response when combined with L-NAME and NE. In the presence of L-NAME, ACh-induced relaxation was unaffected by glibenclamide (10(-5) M) but significantly reduced by apamin (10(-6) M), and almost completely blocked by tetraethylammonium (TEA, 10(-3) M), iberiotoxin (10(-7) M) and 4-aminopyridine (4-AP, 5 x 10(-3) M). The cytochrome P450 inhibitors, 7-ethoxyresorufin (7-ER, 10(-5) M) and miconazole (10(-5) M) also significantly inhibited ACh-induced relaxation. Ouabain (10(-6) M), an inhibitor of Na+, K(+)-ATPase, or K(+)-free solution, also significantly inhibited ACh-induced relaxation. ACh-induced relaxation was not significantly inhibited by 18-alpha-glycyrrhetinic acid (18 alpha-GA, 10(-4) M). These results of this study indicate that ACh-induced endothelium-dependent relaxation of the rabbit femoral artery occurs via a mechanism that involves activation of Na+, K(+)-ATPase and/or activation of both the voltage-gated K+ channel (Kv) and the large-conductance, Ca(2+)-activated K+ channel (BKCa). The results further suggest that EDHF released by ACh may be a cytochrome P450 product.

Effects of Nitric Oxide Synthesis Inhibition on the Blood Pressure Response to Bradykinin in Rats / 대한신장학회잡지

Bradykinin has been known to elicit a pressor effect when administered centrally, and a depressor effect when administered peripherally. The present study was aimed at investigating whether the blood pressure response to bradykinin is dependent on the endogenous generation of nitric oxide (NO). Effects of NG-nitro-L-arginine methyl ester (L-NAME) on the pressor and depressor responses to intracerebroventricularly and intravenously injected bradykinin (5nmol/rat), respectively, were examined in anesthetized rats. Neither the pressor response nor the depressor response was affected by acute parenteral treatment with L-NAME. The pressor and depressor effects of bradykinin were also noted in rats chronically supplemented with L-NAME in drinking water for 4 weeks. Bradykinin caused a relaxation of the isolated thoracic aorta in vitro, which was not affected in the presence of L-NAME. However, bradykinin failed to cause a relaxation of the aorta isolated from rats chronically treated with L-NAME. These findings suggest that endogenous generation of NO may not completely account for the blood pressure responses to bradykinin in rats.

Endothelium dependent Effects of Halothane and Sevoflurane on Isolated Rabbit Aortic Vascular Rings / 대한마취과학회지

This study was aimed to elucidate the endothelium-dependent vascular effects of halothane and sevoflurane on rabbit aortic rings at two conventional concentrations(high induction and low maintenance concentration in human). Isometric tenslon was recorded in isolated aortic rings. Preparations of rabbit thoracic aorta were suspended in Krebs' buffer and aerated with 95% O2 and 5% CO2. One set of the rings had intact endothelium and the other set of the rings had endothelium mechanically denuded. In the first experiments, the rings were precontracted with norepinephrine(NE) of 10-7 M. After tension was stabilized in 10~15 minutes following NE, halothane(1, 2%) or sevoflurane(2, 4%) was bubbled with O2/CO2 gas mixture at increasing concentrations. In the second experiment, O2/CO2 gas mixture only(control rings), halothane 2% or sevoflurane 4 % with O2/CO2, gas mixture was bubbled for 10(-7) minutes prior to and during contraction with NE of 10M. After tension was stabilized following NE, acetylcholine(10(-8)-10(-6) M) was added cumulatively. In the third experiment, the procedure was as same as the second experiment except for that acetylcholine(10(-8)-10(-6) M) was substitued for nitroglycerin (10(-9)-10(-6) M) . The present study demonstated that both of halothane and sevoflurane at high concentration caused a vasoconstriction to 110.7+/-4.2% and 122.4+/-8.4% in vascular rings with intact endothelium, and 106.1+/-1.9% and 118.3+/-3.5% in vascular rings with denuded endothelium, respectively, compared to each control value of 100%. Furthermore, halothane and sevoflurane attenuated the acetylcholine induced relaxing response in NE-precontracted vascular rings with intact endothelium, but did not affect any change of tension in vascular rings with denuded endothelium. Halothane and sevoflurane did not attenuate the nitroglycerin induced relaxing response in NE-precontracted vascular rings with both intact and denuded endothelium. In conclusion, halothane and sevoflurane at high concentration has vasoconstrictory effects on vascular smooth muscles in rabbit aortic rings regardless of presence of endothelium and also attenuated the endothelium-dependent relaxation.

Effects of Na+, K(+)-pump inhibitors on acetylcholine-induced relaxation in the rabbit aorta

The purpose of this study was to investigate the effects of inhibitors of the Na+, K(+)-pump and membrane depolarizing agents on endothelium-dependent acetylcholine-induced relaxation in the rabbit thoracic aorta. Aortic rings were prepared from the rabbit descending thoracic aorta and the contractility of the ring was measured in various conditions such as application of ouabain, exposure to K(+)-free Krebs-Henseleit solution and high K+. Ouabain or exposure to K(+)-free Krebs-Henseleit solution inhibited acetylcholine or sodium nitroprusside-induced relaxation. KCl also inhibited the acetylcholine or sodium nitroprusside-induced relaxation. These results suggest that the Na+, K(+)-pump may play a role in endothelium-dependent acetylcholine-induced relaxation.

Effects of Long-term Antihypertensive Treatment on the Function of Endothelium- dependent Relaxation in Spontaneously Hypertensive Rats / 第二军医大学学报

The effects of long-term treatments with 7 antihypertensive agents on the functions of endothelium-dependent relaxation were studied in spontaneously hypertensive rats (SHR). It was found that captopril, atenolol and dihydrochlorothiazide (DHT) could prevent the endothelium in SHR from impairing, but tetrandrine, nitrendipine, prazosin and dihydralazine could not. The improvement of the function of endothelium-dependent relaxation was not related to the blood pressure lowing.