Relaxant Effect Of Acetylcholine Research Articles

Soluble guanylate cyclase chronic stimulation effects on cardiovascular reactivity in cafeteria diet-induced rat model of metabolic syndrome

Metabolic syndrome is linked to an increased risk of cardiovascular complications by a mechanism involving mainly decreased nitric oxide (NO) bioavailability and impaired NO-soluble guanylate cyclase (sGC)- cyclic guanosine monophosphate (cGMP) signalling (NO-sGC-cGMP). To further develop this scientific point, this study aimed to investigate the effects of long-term treatment with BAY 41–2272 (a sGC stimulator) on cardiovascular reactivity of spontaneously hypertensive rats (SHR) as a model of metabolic syndrome. SHR were randomly divided into 3 groups: control group, cafeteria diet (CD)-fed group and CD-fed group treated daily with BAY 41–2272 (5 mg/kg) by gastric gavage for 12 weeks. In vivo measurements of body weight, abdominal circumference, blood pressure and glucose tolerance test were performed. At the end of the feeding period, ex vivo cumulative concentration-response curves were performed on isolated perfused heart (isoproterenol (0.1 nM - 1 μM)) and thoracic aorta (phenylephrine (1 nM–10 μM), acetylcholine (1 nM–10 μM), and sodium nitroprusside (SNP) (0.1 nM–0.1 μM)). We showed that chronic CD feeding induced abdominal obesity, hypertriglyceridemia, glucose intolerance and exacerbated arterial hypertension in SHR. Compared to control group, CD-fed group showed a decrease in β-adrenoceptor-induced cardiac inotropy, in coronary perfusion pressure and in aortic contraction to phenylephrine. While relaxing effects of acetylcholine and SNP were unchanged. BAY 41–2272 long-term treatment markedly prevented arterial hypertension development and glucose intolerance, enhanced the α1-adrenoceptor-induced vasoconstriction, and restored cardiac inotropy and coronary vasodilation. These findings suggest that BAY 41–2272 may be a potential novel drug for preventing metabolic and cardiovascular complications of metabolic syndrome.

Regulation of smooth muscle contractility by the epithelium in rat tracheas: role of prostaglandin E2 induced by the neurotransmitter acetylcholine.

BackgroundPrevious studies have suggested the involvement of epithelium in modulating the contractility of neighboring smooth muscle cells. However, the mechanism underlying epithelium-derived relaxation in airways remains largely unclear. This study aimed to investigate the mechanism underlying epithelium-dependent smooth muscle relaxation mediated by neurotransmitters.MethodsThe contractile tension of Sprague-Dawley (SD) rat tracheal rings were measured using a mechanical recording system. Intracellular Ca2+ level was measured using a Ca2+ fluorescent probe Fluo-3 AM, and the fluorescence signal was recorded by a laser scanning confocal imaging system. The prostaglandin E2 (PGE2) content was measured using an enzyme-linked immunosorbent assay kit.ResultsWe observed that the neurotransmitter acetylcholine (ACh) restrained the electric field stimulation (EFS)-induced contraction in the intact but not epithelium-denuded rat tracheal rings. After inhibiting the muscarinic ACh receptor (mAChR) or cyclooxygenase (COX), a critical enzyme in prostaglandin synthesis, the relaxant effect of ACh was attenuated. Exogenous PGE2 showed a similar inhibitory effect on the EFS-evoked contraction of tracheal rings. Moreover, ACh triggered phospholipase C (PLC)-coupled Ca2+ release from intracellular Ca2+ stores and stimulated COX-dependent PGE2 production in primary cultured rat tracheal epithelial cells.ConclusionsCollectively, this study demonstrated that ACh induced rat tracheal smooth muscle relaxation by promoting PGE2 release from tracheal epithelium, which might provide valuable insights into the cross-talk among neurons, epithelial cells and neighboring smooth muscle cells in airways.

Pristane-induced arthritis in dark Agouti rat is a relevant model for mimicking vascular dysfunction and lipid paradox in rheumatoid arthritis.

To understand the pathophysiology of cardiovascular (CV) dysfunction in rheumatoid arthritis (RA) is crucial, but limited by the paucity of animal models able to mimic CV impairments. We wanted to determine if the rat model of Pristane-Induced Arthritis (PIA) reproduced cardiometabolic impairments of RA. Dark Agouti rats received an injection of pristane or saline (controls) at day 0. Reactivity to vasoconstrictors and vasodilators was studied in aortic rings and mesenteric arteries at day 28 (acute) and day 120 post-induction (chronic phase). Circulating markers of inflammation, lipid and glucose levels, arthritis and radiographic scores were assessed. In aortic rings, PIA induced a reduced vasoconstriction to phenylephrine and serotonin in both phases of the model. The relaxant effect of acetylcholine was decreased in PIA in acute (P < 0.05) but not in chronic phase. In mesenteric arteries, only the acetylcholine-induced vasorelaxation was impaired in PIA rats in the chronic phase (P < 0.001). Serum interleukin-6 levels were higher, total cholesterol and triglycerides levels were lower in PIA in both phases (P < 0.001) whereas myeloperoxidase activity and blood glucose were unchanged. Adiponectine levels were lower in PIA in acute (P < 0.001) but not in chronic phase. Endothelial function correlated with interleukin-6, total cholesterol levels and arthritis score in aorta but not in mesenteric arteries. As new information, PIA induces endothelial dysfunction in micro-/macro-vascular beds and low lipid levels, like in RA. This model of chronic arthritis might be useful to study CV pathophysiology and to screen new therapeutic options for reducing CV risk in RA.

Pharmacological Study on the Effect of the Aqueous Extract of Mangifera Indicaa Leaves on Vascular Activity of Diabetic Albino Rats

Background: diabetes mellitus is the most common endocrine disease, which is considered one of the most important causes of morbidity and mortality worldwide. Diabetes can affect many different organ systems in the body and can lead to serious complications. These complications can be classified as microvascular or macrovascular. Microvascular complications include nervous system damage, renal system damage and eye damage. Macrovascular complications include cardiovascular disease, stroke and peripheral vascular disease. Objective: it aimed to assess effects of aqueous mango leaves extract on diabetes mellitus. Materials and Methods: aqueous mango leaves extract were assessed for their effects on blood glucose, blood pressure, lipid profiles and body weight in diabetic rats. Also, check out photochemical agents including total phenolics, flavonoids, tannins and antioxidant activity in the aqueous mango leaves extract. Results: aqueous mango leaves extract are rich in total phenols, flavonoides and tannins content, so the antioxidant activity is high. Random blood glucose level and systolic blood pressure were decreased in diabetic rats treated with either aqueous extract of mango leaves or glibenclamide, while, body weight was increased in diabetic rats treated with either glibenclamide or aqueous extract of mango leaves. The contractile responses to norepinephrine were decreased and the relaxant effect of acetylcholine were increased significantly in diabetic rats treated with either glibenclamide or aqueous extract of mango leaves. The treatment of glibenclamide with aqueous mango leaves extract gave the best results with diabetic rats compared to other treatments. Conclusion: aqueous mango leaves extract produced a significant hypoglycemic effect in diabetic rats and improved the diabetes mellitus induced changes in the vascular reactivity, so possibility of its usingas dietary supplements have healthy and therapeuticproperties.

Inhibitors of soluble epoxide hydrolase minimize ischemia-reperfusion-induced cardiac damage in normal, hypertensive, and diabetic rats.

We designed a study to evaluate the cardioprotective effect of two soluble epoxide hydrolase (sEH) inhibitors, 1-(1-propanoylpiperidin-4-yl)-3-(4-trifluoromethoxy)phenyl)urea (TPPU) and trans-4-{4-[3-(4-trifluoromethoxyphenyl)-ureido]cyclohexyloxy}benzoic acid (t-TUCB), in ischemia-reperfusion (IR) model. Cardioprotective effects of the sEH inhibitors were evaluated against IR-induced myocardial damage in hearts from normal, hypertensive, and diabetic rats using Langendorff's apparatus. In addition, the effect of sEH inhibitors on endothelial function was evaluated in vitro and ex vivo using isolated rat thoracic aorta. Ischemia-reperfusion (IR) increased the myocardial damage in hearts from normal rats. IR-induced myocardial damage was augmented in hearts isolated from hypertensive and diabetic rats. Myocardial damage as evident from increase in the activities of lactate dehydrogenase (LDH) and creatine kinase-MB (CK-MB) in heart perfusate was associated with significant decrease in the heart rate and developed tension, and increase in the resting tension in isolated heart. Both sEH inhibitors protected the heart in normal, hypertensive, and diabetic rats subjected to IR injury. The sEH inhibitor t-TUCB relaxed phenylephrine precontracted aorta from normal rats. Relaxant effect of acetylcholine (ACh) was reduced in aortas from diabetic and hypertensive rats compared to normal rats. Pretreatment of sEH inhibitors to diabetic and hypertensive rats increased relaxant effect of ACh on aortas isolated from these rats. Prophylactic treatment with sEH inhibitors decreased myocardial damage due to IR, hypertension and diabetes, and decreased endothelial dysfunction created by diabetes and hypertension. Therefore, inhibitors of sEH are useful probes to study cardiovascular pathology, and inhibition of the sEH is a potential approach in the management of IR-induced cardiac damage and endothelial dysfunction-related cardiovascular disorders.

Reduction of NO-mediated Relaxing Effects in the Thoracic Aorta in an Experimental Chronic Kidney Disease Mouse Model.

Chronic kidney disease (CKD) is known to frequently cause cardiovascular events. However, it is unclear how renal dysfunction affects the vascular response. We herein studied the effects of renal dysfunction on the aortic behavior in adenine-fed mice, investigating mechanisms underlying the occurrence of cardiovascular events in CKD patients. Biochemical analyses of the plasma creatinine, blood urea nitrogen (BUN) and glucose levels and measurements of the blood pressure were performed using C57BL/6 mice fed with and without an adenine-containing diet. The relaxing effects of acetylcholine (ACh) or sodium nitropurusside (SNP) and effects of NO synthase (NOS) inhibitors on the contractions induced by phenylephrine (PE) were measured in endothelium-intact aortas obtained from both mice. The mice fed 0.25% adenine for four weeks showed greater plasma creatinine and BUN concentrations than the control mice, suggesting that adenine-fed mice are a useful CKD model. Furthermore, ACh relaxed the PE-stimulated, endothelium-intact aortas, the effect of which was less potent in the adenine-fed mice than in the control mice. In contrast, the degree of SNP-induced relaxation of the aortas was the same in the adenine-fed mice and control mice. The α1-adrenergic agonist, PE, induced more potent absolute tension of the endothelium-intact aortas in the CKD model mice than in the control mice, while the NOS inhibitors, N-nitro-L-arginine (LNA) and asymmetric dimethylarginine (ADMA) enhanced the contraction effects of PE in both mice. The findings of this study indicate that spontaneous and stimulated NO release from the endothelium is decreased in the CKD model mouse aorta. The NO-mediated correlation between renal and elastic arterial endothelial dysfunction is suggested to be a cause of cardiovascular events in patients with CKD.

The analysis of transduction mechanisms associated with an acute action of homocysteine on isolated rat femoral artery.

The present study was undertaken in order to examine transduction mechanism involved in the single application of 100 μM homocysteine (Hcy) on isolated rat femoral artery (RFA) rings equilibrated on the basal tone; to establish if a single application of 100 μM Hcy alters contractile effect of phenylephrine (Phe), or oppositely the relaxant effect of acetylcholine (ACh) or bradykinin (BK) after 60-min-long incubation of 100 μM Hcy; and finally to identify morphological changes on the vascular wall after a 24-h-long incubation of 100 μM Hcy. Hcy produced contractile response of intact RFA, which was increased after endothelial denudation, while decreased by urapidil (an α1 receptor blocker), nifedipine (a voltage-gated L-type Ca++ channel blocker) or indomethacin (a cyclooxygenase inhibitor). The initial RFA contraction evoked by Phe was further increased by the single addition of Hcy, which was not the case when ouabain (an inhibitor of Na+/K+-ATPase) was preincubated. After 60-min-long incubation of Hcy relaxant actions of ACh and BK were unaltered, equieffective and equipotent. A 24-h-long incubation of RFA rings with Hcy produced an impairment of vascular endothelium, expressed as a minor or more pronounced interruption of endothelial cells.

N G-Monomethyl-l-arginine and NG-nitro-l-arginine inhibit endothelium-dependent relaxations in human isolated omental arteries

The L-arginine analogues NG-monomethyl-L-arginine (L-NMMA, 10(-4) M) and NG-nitro-L-arginine methyl ester (L-NAME, 10(-4) M), which specifically inhibit the synthesis of nitric oxide from L-arginine, significantly reduced acetylcholine-induced endothelium-dependent relaxations in rings of human omental arteries. The inhibitory potency of L-NMMA and L-NAME was similar. Addition of L-NMMA or L-NAME to the organ bath did not induce any significant changes in the resting tension of the tissues. The effects of L-NMMA were reversed by L-arginine (3 x 10(-4) M). The L-NMMA enantiomer, D-NMMA (10(-4) M), did not influence either the basal tone of the preparation or the relaxing effects of acetylcholine. Arterial relaxations induced by sodium nitroprusside (10(-6) M) were not influenced by incubation with L-NMMA or L-NAME. These results suggest that endothelium-dependent relaxations in human omental arteries are mediated by the endogenous and substrate-specific generation of nitric oxide from L-arginine.

Investigation of the effects of Prosopis farcta plant extract on Rat's aorta

Ischemic heart diseases are the most common causes of death in the developed and developing societies. Because vegetable based medications have lower side effects and are well adapted to body’s physiology, a global trend to use these kinds of medications for cardiovascular diseases is increasing. To investigate the effect of Prosopis farcta plant extract (P. F. P. E) on rat’s thoracic aorta. P. farcta plant extract was firstly prepared. Then 2 cm of rat’s thoracic aorta was dissected and was divided into 4 pieces of 5 mm. After contraction of these pieces by phenylephrine (1 µm), different dosages of plant extraction (0.5, 1 and 2 mg/ml) were examined and the effect of P. F. P. E on rat’s aorta with and without endothelium layer was measured. Different dosages of P. farctaextract (1 and 2 mg/ml) at the presence and absence of L- NAME (a nitric oxide synthetase inhibitor) was examined. P. farcta plant extract showed a dose dependent relaxing effect on contracted aorta. The relaxing effect of P. F. P. E on aorta with endothelium was more significant than that on aorta without endothelium in the different dosages (p < 0.05). The relaxing effect of P. F. P. E in the presence of L- NAME was reduced significantly (p < 0.05). The relaxing effect of P. F. P. E was more than that by acetylcholine (p < 0.05). Relaxing effect of acetylcholine was inhibited by atropine but it did not show any effect on the relaxing effect of P. F. P. E (p < 0.001). P. farcta plant extract showed a dose dependent as well as an endothelium dependent relaxing effect on thoracic aorta in rats. Endothelium layer showed an important role in the relaxing effect of P. F. P. E on rat’s aorta. Also nitric oxide had a significant role on the relaxing effect of P. F. P. E. Key words: Aorta, endothelium layer, prosopis farcta, relaxing effect.

The Effect of Experimental Diabetes on the Twenty‐Four‐Hour Pattern of the Vasodilator Responses to Acetylcholine and Isoprenaline ın the Rat Aorta

The aim of this study was to investigate whether time‐dependent variations in the relaxant effect of acetylcholine, an endothelium‐dependent vasorelaxant via muscarinic receptors, and isoprenaline, a nonselective β‐adrenoceptor agonist in rat aorta, are influenced by streptozotocin (STZ)‐induced experimental diabetes. Adult male rats were divided randomly into two groups: control and STZ‐induced (STZ, 55 mg/kg, intraperitoneal) diabetes. The animals were synchronized to a 12∶12 h light‐dark cycle (lights on 08∶00 h) and sacrificed at six different times of day (1, 5, 9, 13, 17, and 21 hours after lights on; HALO) eight weeks after STZ injection. The in vitro responsiveness of thoracic aorta rings obtained from control and diabetic rats to acetylcholine (10−9–10−5 M) and isoprenaline (10−10–10−3 M) was determined in six different times. EC50 (the concentration inducing half of the maximum response) values and maximum responses were calculated from cumulative concentration‐response curves of the agonists and were analyzed with respect to time and STZ treatment. Treatment, time, and interactions between treatment and time were tested by two‐way analysis of variance (ANOVA). To analyze differences due to biological time, one‐way ANOVA was used. STZ treatment did not significantly change EC50 values or maximum responses for both agonists. There were statistically significant time‐dependent variations in the EC50 values for isoprenaline and maximum responses for both acetylcholine and isoprenaline in control groups by one‐way ANOVA, but significant time‐dependent variations disappeared in the aortas isolated from STZ‐induced diabetic rats. The vasodilator responses to acetylcholine and isoprenaline failed to show any significant interaction (treatment×time of study) between STZ treatment and time of sacrifice in both EC50 values and maximum responses by two‐way ANOVA. These results indicate there is a basic temporal pattern in the responses to acetylcholine and isoprenaline in rat aorta which continues in diabetes. It is shown for the first time that experimental diabetes does not change the 24 h pattern of responses to acetylcholine and isoprenaline, and that time‐dependent variations in the responses to these agonists disappear in diabetic animals. Although further studies are required to define the underlying mechanism(s) of these findings, results suggest that experimental diabetes can modify the time‐dependent vasorelaxant responses of rat aorta. This may help to understand the circadian rhythms in cardiovascular physiology and pathology or in drug effects in diabetes.

Angiotensin II type 1 receptor antagonism improves endothelial vasodilator function in L-NAME-induced hypertensive rats by a kinin-dependent mechanism

This study was designed to investigate the ability of a chronic blockade of angiotensin II type 1 receptors with losartan to reverse the endothelial dysfunction present in N-nitro-L-arginine methyl ester (L-NAME)-treated hypertensive rats and the possible dependence of this effect on bradykinin B2-receptor activation. Rats treated with L-NAME alone (60 mg/kg per day for 8 weeks) or with L-NAME + losartan, L-NAME + icatibant (a bradykinin B2-receptor antagonist) and L-NAME + losartan + icatibant were studied. Losartan, icatibant or losartan + icatibant were co-administered with L-NAME during the last 4 weeks of the experiment. Endothelial nitric oxide synthase gene expression in aortic tissues, plasma nitrite/nitrate concentrations, the relaxant effect of acetylcholine on norepinephrine-precontracted aortic rings and 6-keto-PGF1alpha release from aortic rings were used as markers of the endothelial function. Rats treated with L-NAME alone and L-NAME + icatibant showed, as compared with untreated animals, a clear-cut increase in systolic blood pressure and a decrease of all the markers of endothelial function evaluated. In L-NAME-rats, administration of losartan reduced the systolic blood pressure and restored endothelial nitric oxide synthase gene expression, plasma nitrite/nitrate levels, the relaxant activity of acetylcholine on aortic rings and the generation of 6-keto-PGF1alpha from the aortic tissues. Co-administration of icatibant with losartan blunted the stimulatory effect of losartan on the markers of endothelial function evaluated. These results demonstrated that losartan is capable of reversing the endothelial vasodilator dysfunction in L-NAME-induced hypertensive rats, and that the beneficial effect of losartan is mediated by bradykinin B2-receptor activation.

Vasorelaxant effects of the chronic treatment with melatonin on mesenteric artery and aorta of spontaneously hypertensive rats.

To investigate the effect of a chronic treatment with melatonin on arterial pressure and a possible improvement of the vascular muscarinic and NO synthase (NOS) pathways in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. Mean arterial pressure (MAP), systolic (SBP), diastolic blood pressure (DBP), and heart rate (HR) were evaluated in conscious rats treated with 30 mg/kg per day of melatonin during 4 weeks. Changes in MAP were evaluated following an intravenous injection of the NOS inhibitor N-omega-nitro-L-arginine methyl ester (L-NAME). Relaxant effects of acetylcholine (Ach), sodium nitroprusside (SNP), and the calcium ionophore A23187 were examined on mesenteric beds and aortic rings with or without treatment with melatonin. Melatonin produced a significant reduction of MAP, SBP, DBP and HR in SHR (P < 0.05). L-NAME increased the MAP of melatonin-treated SHR by the same magnitude as that of WKY rats which was significantly higher than that of non-treated SHR (P< 0.05). Melatonin treatment improved the maximal relaxation of mesenteric arteries to A23187 in SHR (P < 0.001) to the WKY level and caused a slight increment in Ach- and A23187-induced vasodilations in aorta from SHR and WKY rats (P < 0.05). The present study showed that melatonin exerted a bradycardic and an antihypertensive action in SHR. The enhancement by melatonin of the endothelium-dependent vasodilation (Ach and/or A23187) in mesenteric artery and aorta from SHR and WKY rats and the higher increase in MAP following L-NAME treatment in melatonin-treated SHR suggest the contribution of an improved vascular NOS pathway activity in the hypotensive effect of melatonin.

Study of Garlic Extracts and Fractions on Cholesterol Plasma Levels and Vascular Reactivity in Cholesterol-Fed Rats

Garlic is known for its pharmacologic and nutritional properties. In previous studies, garlic elicited a reduction in plasma levels of lipids by inhibiting hepatic cholesterol synthesis. The aim of this study was to investigate in an in vivo model the effects of garlic extract and some fractions on cholesterol levels and vascular reactivity in cholesterol-fed rats. Rats were fed a cholesterol-enriched diet for 16 wk and were divided into 10 groups as follows: control and hypercholesterolemic diet groups, 4 groups fed frozen garlic fractions and 4 groups fed raw garlic fractions with different doses. Blood samples were obtained to analyze HDL and LDL cholesterol levels. After treatment, rats were killed. The heart, liver and kidneys were weighed; the aorta was isolated, mounted in organ chambers and vascular reactivity was tested. Plasma concentration of cholesterol was 58 mg/dL (100%) at the beginning of the study and increased to 102 mg/dL (153%; hypercholesterolemic group) at the end of the treatment. Plasma total cholesterol decreased in all groups treated with garlic; moreover, this effect was higher in rats fed raw garlic fractions and extracts. LDL decreased significantly with respect to the hypercholesterolemic group in all groups treated with garlic fractions and extracts (P: < 0.01); however, an increase in HDL was found in those treated with frozen fractions and extracts. The liver:body weight ratio decreased in all treated groups. The relaxing effect of acetylcholine (ACh) was enhanced in arteries contracted with noradrenaline (NE). These data suggest that garlic fractions could prevent diet-induced hypercholesterolemia and vascular alterations in the endothelium-dependent relaxation associated with atherosclerosis.

The effects of histamine on the isolated mouse uterus.

1. A study is made of the contractile and relaxant effects, and mechanism of action, of histamine on isolated uterus from mice treated with diethylstilboestrol, employing acetylcholine and adrenaline as contractile and relaxant standard agents. 2. Concentration-response curves for histamine agonists were obtained in the absence and presence of selective histaminergic blocking drugs (clemizole, ranitidine and thioperamide) and indomethacin. A number of experiments were carried out in uterus from reserpinised mice. Concentration-response curves for acetylcholine and adrenaline were also obtained in the absence and presence of their selective antagonist (atropine and propranolol). 3. In isolated oestrogenised mouse uterus, histamine and acetylcholine produced a concentration-related contractile response. When the uterus was precontracted with KCl, histamine at lower doses produced a slight contraction, though in the presence of clemizole it induced concentration-related relaxation, reminiscent of that produced by adrenaline. Atropine and propranolol antagonised the contractile and relaxant effects of acetylcholine and adrenaline, respectively. 4. In isolated uterus from reserpinised mice, histamine and 2-pyridylethylamine, but not 4-methylhistamine, produced a concentration-related contractile response. Ranitidine potentiated the contractile effect of histamine, though clemizole--in the presence of ranitidine--competitively antagonised the contractile effect of histamine (pA2 = 10.50 +/- 0.81). The concentration-relaxant curve of histamine in the presence of clemizole was not modified by ranitidine or indomethacin, but shifted to the right with thioperamide. The same displacement was also observed in the presence of clemizole plus ranitidine. 5. In mouse isolated uterus, histamine mainly produced contraction mediated by histamine H1-receptors, though the existence of histamine H2- or H3-receptors mediating relaxation could not be excluded.

Effect of Time on Endothelium-Dependent Relaxations in Mice and Rat Thoracic Aortas

Temporal variations in the endothelium-dependent relaxant effects of acetylcholine (ACh) in mice and histamine (HA) in rat thoracic aorta have been studied. The relaxations induced by higher concentrations of ACh and HA were significantly dependent on the time the tissues were obtained. However, neither EC 50 (the concentration inducing half of the maximum response) values for ACh and HA, nor K B (antagonist dissociation constant) values for atropine and diphenhydramine were found to be statistically significant depending upon the time of obtaining aorta preparations. These results show that the in vitro responsiveness of mice and rat thoracic aortas to endothelium-dependent relaxant effects of ACh and HA, respectively, changes over a 24-h period. These variations might be dependent on a temporal rhythm in post-receptor events, i.e., guanylate cyclase-cGMP-phosphodiesterase system which mediates responses to endothelium-derived relaxing factor(s).

Impaired endothelium-dependent relaxation by adrenomedullin in monocrotaline-treated rat arteries

The effects of adrenomedullin were evaluated in isolated vascular rings from rats treated with monocrotaline (60 mg/kg, s.c.) causing pulmonary hypertension and right ventricular hypertrophy within 3 to 4 weeks. Sham animals (NaCl-treated rats) were used for comparison. The relaxing effects of adrenomedullin (10 −8 M) and acetylcholine (10 −6 M) were determined in thoracic aorta and pulmonary artery rings precontracted with phenylephrine (10 −7 M). In sham animals, adrenomedullin caused significant vasorelaxation of aorta and pulmonary artery although of different amplitude (24±3% and 40±2%, respectively). A greater relaxation was observed in response to acetylcholine. Monocrotaline-treated rats exhibited a reduction in adrenomedullin relaxation in pulmonary artery (54 and 68% loss of effect, at 3 and 4 weeks, respectively, P<0.01 vs. sham) and comparable reductions in acetylcholine responses. The decrease in adrenomedullin relaxing effect was less pronounced in aorta than in pulmonary artery, suggesting a distinct tissue sensitivity to monocrotaline. In contrast, the relaxing effect of acetylcholine on aorta was decreased at 4 weeks (36% reduction, P<0.01 vs. sham). In this model, the adrenomedullin-induced relaxation of the pulmonary artery was impaired due to a severe endothelial dysfunction which may contribute partly to the evolving pathophysiological process.

Papaverine-induced and endothelium-dependent relaxation in the isolated rat aortic strip.

In the present study, we aimed to obtain further evidence in favour of the hypothesis that nitric oxide (NO) is a major mediator of endothelium-dependent vasorelaxation and to clarify whether NO plays a role in papaverine-induced vasorelaxation. The relaxant effects of acetylcholine (Ach), acidified NaNO2 or papaverine were investigated on isolated helical strips of the rat thoracic aorta precontracted with phenylephrine in an organ bath containing Krebs solution aerated with 95% O2 and 5% CO2. The relaxation was quantified as % peak reduction of phenylephrine contracture. Saponin abolished the relaxant effects of Ach completely whereas it had no effect on the responses to acidified NaNO2 or papaverine. NG-nitro-L-arginine (L-NOARG) reduced the effects of Ach significantly, but it was ineffective on the relaxation induced by acidified NaNO2. The inhibitory action of L-NOARG was partly restored by L-arginine, but not by D-arginine. Hemoglobin, hydroxocobalamin and hydroquinone exhibited significant inhibition on the relaxation evoked by Ach and acidified NaNO2. L-NOARG, hydroxocobalamin and hydroquinone caused only limited but significant decrease in the relaxation due to papaverine. This phenomenon was also observed by increasing phenylephrine concentration leading to an enhancement in the contraction. Our findings strongly support the view that Ach-induced relaxation of rat aorta strips is mediated by free NO released from the endothelium and the results suggest that NO may indirectly contribute to papaverine-induced relaxation.

Chronic hypoxia differentially alters the responses of pulmonary arteries and veins to endothelin-1 and other agents

The effects of chronic hypoxia on the responses of rat large pulmonary arteries and veins to vasoactive agents have been examined. Endothelin-1-induced contractions of pulmonary arteries and pulmonary veins were reduced by chronic hypoxia. In contrast, chronic hypoxia augmented sarafotoxin 6c-induced contractile responses in pulmonary veins but not in pulmonary arteries. Chronic hypoxia augmented the constrictor effect of phenylephrine in pulmonary arteries, but not in pulmonary veins. The thromboxane receptor agonist, U46619 (9,11-dideoxy-9 α,11 α-epoxy-methanoprostaglandin f 2α) contracted pulmonary arteries and pulmonary veins, and although maximal responses were not altered in chronically hypoxic preparations, the EC 50 value in pulmonary arteries was increased following chronic hypoxia. The relaxant effects of acetylcholine and isoprenaline on pulmonary arteries were potentiated by chronic hypoxia. In contrast, ionomycin-mediated relaxations of pulmonary arteries and pulmonary veins were reduced, while sodium nitroprusside-induced relaxation of pulmonary arteries and veins were not altered by chronic hypoxia. Previous studied have looked primarily at the effects of chronic hypoxia on pulmonary arteries. This data provides evidence that chronic hypoxia also causes selective changes in the reactivity of large pulmonary veins.

ATP-sensitive potassium channels in cultured arterial segments.

Organ cultures of arteries have been used to study growth responses, proliferation, and contractility. However, the function of specific-ion channels in cultured arteries has not been investigated. ATP-sensitive K+ (KATP) channels play an important role in the control of arterial tone. The goal of this study was to determine the functional state of KATP channels in arteries kept in culture. Segments from rabbit mesenteric arteries were cultured in for 2-7 days. To explore the properties of KATP channels, the effects of KATP-channel modulators and other vasoactive substances on isometric force, density, and modulation of KATP currents in single smooth muscle cells isolated from cultured vessels were examined. Isometric contractions were measured with a resistance-vessel myograph. Whole cell KATP currents were recorded with the patch-clamp technique. Membrane capacitance and KATP-current density in single smooth muscle cells from freshly dissected (control) and cultured arteries were not altered. At -60 mV, glibenclamide-sensitive currents in the presence of the K(+)-channel opener pinacidil were -4.7 +/- 1.2, -4.7 +/- 0.6, and -4.6 +/- 0.7 pA/pF for control and 2- and 4-day arteries, respectively. Inhibitory modulation of KATP currents in arterial smooth muscle also remained intact for 4 days in culture; the vasoconstrictor histamine (10 microM) reduced glibenclamide-sensitive currents in the presence of pinacidil by 61.2 +/- 2.8, 42.4 +/- 10.1, and 41.2 +/- 6.1% for control and 2- and 4-day arteries, respectively. Pinacidil relaxed control and cultured arteries (1-7 days) in a dose-dependent manner. Half-maximal effective concentrations of pinacidil were 0.42, 0.24, 0.23, and 0.51 microM for control and 2-, 4-, and 7-day arteries, respectively, whereas maximal relaxations to pinacidil were 62.9, 47.5, 37.5, and 55.7% for control and 2-, 5-, and 7-day arteries, respectively. Histamine, norepinephrine, and serotonin constricted cultured arteries, although responses to histamine and norepinephrine diminished by 30-50% after 5 days in culture. The relaxant effect of acetylcholine was not maintained in cultured arteries. Sodium nitroprusside, however, effectively relaxed arteries cultured for 2-7 days. The data indicate that with the culture model described, KATP channels in arterial smooth muscle remained functional and contractile responses in arterial segments were maintained for up to 7 days. These results suggest that this approach can be used to study either long-term regulation of KATP channels or the role of this channel type in growth responses.

The effect of oophorectomy on mechanical properties of rabbit cerebral and coronary isolated small arteries

OBJECTIVE: Our purpose was to study the effect of oophorectomy on the passive and active mechanical characteristics of rabbit small cerebral and small coronary arteries. STUDY DESIGN: Ring preparations of small cerebral and small coronary arteries from rabbits that had undergone oophorectomy and sham operation were mounted on myographs 6 weeks after operation. Experiments were performed as follows. (1) concentration-response relations for vasopressin (10 -11 to 10 -7 mol/L), U46619 (10 -10 to 10 -6 mol/L), 5-hydroxytryptamine (10 -7 to 10 -5 mol/L), and endothelin (10 -13 to 10 -7 mol/L); (2) relaxing effects of acetylcholine (10 -8 to 10 -4 mol/L); (3) length-tension relations after addition of high potassium (124 mmol/L), vasopressin (10 -7 mol/L), and a mixture composed of potassium (124 mmol/L), vasopressin (10 -7 mol/L), and prostaglandin F 2α (10 -5 mol/L); (4) calculation of vessel morphologic features and determination of hydroxyproline as a measure of collagen content. RESULTS: Oophorectomy did not influence basal tone, relaxant effects of acetylcholine, vessel morphologic features, elastic characteristics, or hydroxyproline content of the vessels. However, in cerebral arteries at a normalized lumen diameter, oophorectomy induced a marked increase in the force development after stimulation with agonists but not after depolarization with high potassium. The reason for this was a leftward shift in the active length-tension curves (vasopressin activation). In coronary arteries none of these changes were seen after oophorectomy. CONCLUSION: These data demonstrate that withdrawal of ovarian hormones changes the position of the active length-tension curve for pharmacomechanical but not electromechanical coupling of small cerebral arteries without interference with the elastic characteristics of these vessels. (Am J Obstet Gynecol 1996;175:1272-80.)