Perfused Tail Artery Research Articles

Modulatory effect of laser irradiation on mastoparan-7-induced contraction.

Mastoparan-7 activates guanine nucleotide-binding proteins (G-proteins) and stimulates both apoptosis and increases in cytoplasmic calcium concentration and may induce smooth muscle contraction. The primary aim of the present study was to evaluate the modulatory effect of laser stimulation on vascular smooth muscle contraction induced by direct stimulation of G-protein with mastoparan-7. Experiments were performed on isolated and perfused tail arteries of Wistar rats. Contraction force in the model was measured by increased levels of perfusion pressure with a constant flow. Irradiation treatment was applied directly to the blood vessels. The laser was applied in increasing doses of 10 mW (E=1.8 J), 30 mW (E=5.5 J) and 110 mW (E=19.8 J). Time of exposure was 3 min for each irradiation. In the laser-stimulated arteries, a significant and dose-dependent decrease was observed. The half maximal effective concentration values were 4.43±2.2x10-8, 2.4±0.56x10-7, 3.2±0.72x10-7 and 7.7±0.3x10-7 M/l in the control and 10, 30 and 110 mW laser irradiation groups, respectively. Significant (P<0.001) changes were identified for all laser treatment groups in comparison with the control. When analyzing the function of calcium ion (Ca2+) stores was analyzed, a significant inhibition of influx from both intra- and extracellular Ca2+ stores was observed. The results from the present study suggested that contraction induced by direct activation of G-protein with mastoparan-7 may by effectively inhibited by laser radiation, and that the effect was associated with an inhibition of Ca2+ influx from both intracellular and extracellular Ca2+ stores.

Common umbilical cord insertion in a monochorionic, monoamniotic twin pregnancy - a case report.

Ischemia and reperfusion remain inseparable elements of numerous medical procedures such as by-pass surgery, organ transplantation or other cardiology and intervention radiology. The contraction of the smooth muscle of the vessel is considered to be one of the basic components leading to impaired perfusion, an increase in the oxygen deficit of the endothelium of the vessel, and subsequently also to tissues vascularized by the vessel.Main aim of this study was to evaluate the effect of ischemia and reperfusion on vascular smooth muscle cells stimulated pharmacologically with mastoparan-7 (direct G-protein activator) in comparison to stimulation of G-protein coupled receptor agonist - phenylephrine, and direct calcium channel activator - Bay K8644.Experiments were performed on isolated and perfused tail artery of Wistar rats. Contraction force in our model was measured by increased level of perfusion pressure with a constant flow.Concentration-response curves obtained for phenylephrine, mastoparan-7 and Bay K8644 presented a sigmoidal relation. Ischemia induced hyporreactivity of vessels, whereas during reperfusion the significant time related hyperreactivity for phenylephrine and mastoparan-7 only but not for Bay K8644. These reactions were secondary to the modulation of calcium influx from intra- and extracellular calcium stores.Results of our experiments suggest that mastoparan-7 significantly induces contraction of vascular smooth muscle cells not only for controls but in the presence of ischemia and reperfusion too. Potential therapeutic applications of the observed reactions are important. They may include regenerative processes within the nervous system, studies on the improvement of blood flow within the microcirculation, or antimicrobial activity. Modulation of the G protein-phospholipase C response may also be an interesting point of action of future drugs modifying the response to stimulation during ischemia in particular, such activities could take place during the transport of organs for transplantation.

Effect of reperfusion on vascular smooth muscle reactivity in three contraction models

BackgroundIschemia and reperfusion remain inseparable elements of numerous medical procedures such as by-pass surgery, organ transplantation or other cardiology and intervention radiology. The contraction of the smooth muscle of the vessel is considered to be one of the basic components leading to impaired perfusion, an increase in the oxygen deficit of the endothelium of the vessel, and subsequently also to tissues vascularized by the vessel.Main aim of this study was to evaluate the effect of ischemia and reperfusion on vascular smooth muscle cells stimulated pharmacologically with mastoparan-7 (direct G-protein activator) in comparison to stimulation of G-protein coupled receptor agonist - phenylephrine, and direct calcium channel activator - Bay K8644. Material and methodsExperiments were performed on isolated and perfused tail artery of Wistar rats. Contraction force in our model was measured by increased level of perfusion pressure with a constant flow. ResultsConcentration-response curves obtained for phenylephrine, mastoparan-7 and Bay K8644 presented a sigmoidal relation. Ischemia induced hyporreactivity of vessels, whereas during reperfusion the significant time related hyperreactivity for phenylephrine and mastoparan-7 only but not for Bay K8644. These reactions were secondary to the modulation of calcium influx from intra- and extracellular calcium stores. ConclusionsResults of our experiments suggest that mastoparan-7 significantly induces contraction of vascular smooth muscle cells not only for controls but in the presence of ischemia and reperfusion too. Potential therapeutic applications of the observed reactions are important. They may include regenerative processes within the nervous system, studies on the improvement of blood flow within the microcirculation, or antimicrobial activity. Modulation of the G protein-phospholipase C response may also be an interesting point of action of future drugs modifying the response to stimulation during ischemia in particular, such activities could take place during the transport of organs for transplantation.

Anti-atherogenic properties of resveratrol: 4-week resveratrol administration associated with serum concentrations of SIRT1, adiponectin, S100A8/A9 and VSMCs contractility in a rat model.

Resveratrol (3, 4', 5-trihydroxy-trans-stilbene) is a natural, non-flavonoid polyphenol that exerts protective properties against atherosclerosis-associated endothelial dysfunction and senescence. The present study aimed to assess the influence of resveratrol on vascular contractility and molecular factors including sirtuin-1 (SIRT1), adiponectin and calprotectin (S100A8/A9) that are considered to be important elements of atherogenesis. A total of 17 male rats were divided into a control and treatment group and administered resveratrol or a placebo. Pharmacometrics were performed on an isolated and perfused tail artery. Serum SIRT1, adiponectin and S100A8/A9 levels were quantified using an ELISA assay. The level of SIRT1 in the control and treatment groups at time 0 was 4.26 and 4.45 ng/ml, respectively. SIRT1 in the control and treatment groups following 2 weeks of treatment was 4.59 and 6.86 ng/ml, respectively (P<0.05) and following 4 weeks of treatment was 4.15 and 6.38 ng/ml, respectively (P<0.05). The level of adiponectin in the control and treatment groups at time 0 was 1.24 and 1.21 ng/ml, respectively. Following 2 weeks of treatment, the level of adiponectin in the control and treatment groups was 1.22 and 1.2 ng/ml, respectively (P>0.05) and following 4 weeks of treatment was 1.26 and 1.58 ng/ml, respectively (P<0.05). The S100A8/A9 level in control and treatment groups at time 0 was 0.39 and 0.33 ng/ml, respectively. The level of S100A8/A9 in control and treatment groups following 2 weeks of treatment was 0.37 and 0.35 ng/ml, respectively (P>0.05) and following 4 weeks of treatment was 0.34 and 0.32 ng/ml, respectively (P>0.05). EC50 values obtained for phenylephrine in resveratrol-pretreated arteries were significantly higher than controls in the presence and absence of A7-hydrochloride (P<0.05). The results of the present study indicate a significant increase in the concentration of SIRT1 and adiponectin in the resveratrol-pretreated group (P<0.05). S100A8/A9 serum concentrations remained unchanged. Reactivity of resistant arteries was significantly reduced for resveratrol-pretreated vessels and this effect was partially independent of phosphodiesterase (PDE1). Additionally, there was a synergistic interaction observed between resveratrol and the PDE1 inhibitor.

Resveratrol Increases Serum BDNF Concentrations and Reduces Vascular Smooth Muscle Cells Contractility via a NOS-3-Independent Mechanism

Resveratrol is a polyphenol that presents both antineuroinflammatory properties and the ability to interact with NOS-3, what contributes to vasorelaxation. Brain-derived neurotrophic factor (BNDF), a molecule associated with neuroprotection in many neurodegenerative disorders, is considered as an important element of maintaining stable cerebral blood flow. Vascular smooth muscle cells (VSMCs) are considered to be an important element in the pathogenesis of neurodegeneration and a potential preventative target by agents which reduce the contractility of the vessels. Our main objectives were to define the relationship between serum and long-term oral resveratrol administration in the rat model, as well as to assess the effect of resveratrol on phenylephrine- (PHE-) induced contraction of vascular smooth muscle cells (VSMCs). Moreover, we attempt to define the dependence of contraction mechanisms on endothelial NO synthase. Experiments were performed on Wistar rats (n = 17) pretreated with resveratrol (4 weeks; 10 mg/kg p.o.) or placebo. Serum BDNF levels were quantified after 2 and 4 weeks of treatment with ELISA. Contraction force was measured on isolated and perfused tail arteries as the increase of perfusion pressure with a constant flow. Values of serum BNDF in week 0 were 1.18 ± 0.12 ng/mL (treated) and 1.17 ± 0.13 ng/mL (control) (p = ns). After 2 weeks of treatment, BDNF in the treatment group was higher than in controls, 1.52 ± 0.23 ng/mL and 1.24 ± 0.13 ng/mL, respectively. (p = 0.02) Following 4 weeks of treatment, BDNF values were higher in the resveratrol group compared to control 1.64 ± 0.31 ng/mL and 1.32 ± 0.26 ng/mL, respectively (p = 0.031). EC50 values obtained for PHE in resveratrol pretreated arteries were significantly higher than controls (5.33 ± 1.7 × 10−7 M/L versus 4.53 ± 1.2 × 10−8 M/L, p < 0.05). These results show a significant increase in BDNF concentration in the resveratrol pretreated group. The reactivity of resistant arteries was significantly reduced for resveratrol pretreated vessels and this effect was partially NOS-3 independent.

2,4,6-Trimethyl-N-[3-(trifluoromethyl)phenyl]benzenesulfonamide increases calcium influx in lipopolisaccharide-pre-treated arteries.

It has been demonstrated that 2,4,6-trimethyl-N-[3-(trifluoromethyl)phenyl]benzenesulfonamide (m-3M3FBS) activates phospholipase C (PLC) and stimulates apoptosis in smooth muscle cells, which may increase vascular reactivity. The primary aim of the present study was to evaluate the physiological effects of the direct stimulation of PLC by m-3M3FBS on vascular smooth muscle reactivity in arteries pre-treated with lipopolysaccharides (LPS) as a model of septic shock. Experiments were performed on isolated and perfused tail arteries of Wistar rats. The contraction force in the model was measured by assessing increases in perfusion pressure at a constant flow. Parameters describing the concentration-response curves (CRCs) obtained for phenylephrine and arginine-vasopressin in the presence of LPS confirmed a decrease in vessels reactivity. In comparison with the controls, m-3M3FBS treatment caused a significant increase in LPS-untreated as well as pre-treated arteries. Furthermore, in the presence of m-3M3FBS, calcium influx from intra- as well as extracellular calcium stores was significantly higher for LPS-untreated and pre-treated arteries. The results of the present study suggested that m-3M3FBS significantly increased the reactivity of vascular smooth muscle cells pre-treated with LPS by increasing the calcium influx from intra- and extracellular calcium stores. Further studies investigating this mechanism are required to evaluate whether this pathway may be a potential therapeutic strategy to treat sepsis.

Effect of 2,4,6-trimethyl-N-[3-(trifluoromethyl)phenyl]benzene-sulfonamide on calcium influx in three contraction models.

2,4,6-Trimethyl-N-[3-(trifluoromethyl)phenyl]benzenesulfonamide (m-3M3FBS) activates phospholipase C and stimulates apoptosis; however, in smooth muscle cells it may increase the perfusion pressure. The main aim of the present study was to evaluate the physiological effect of direct stimulation of phospholipase C on vascular smooth muscle reactivity using three contraction models. Experiments were performed on the isolated and perfused tail artery of Wistar rats. The contraction force in the present model was measured by an increased level of perfusion pressure with a constant flow. Concentration-response curves (CRCs) obtained for phenylephrine, arg-vasopressin, mastoparan-7 and Bay K8644 presented a sigmoidal association. In comparison to the control curves, CRCs in the presence of m-3M3FBS were significantly shifted to the left except for Bay K8644. Analyses of calcium influx suggest that in the presence of m-3M3FBS the calcium influx from intra- and extracellular calcium stores was significantly higher. The results of the present experiments suggest that m-3M3FBS significantly increases the reactivity of vascular smooth muscle stimulated with metabotropic receptors or G-protein by an increase in calcium influx from intra- and extracellular calcium stores. The current knowledge regarding the apoptotic pathway shows the significance of calcium ions involved in this process, thus, m-3M3FBS may induce apoptosis by an increase of cytoplasmic calcium concentration; however, simultaneously, the use of this mechanism in therapy must be preceded by a molecular modification that eliminates a possible vasoconstriction effect.

Cyclosporine-A, but not tacrolimus significantly increases reactivity of vascular smooth muscle cells.

Application of cyclosporine-A (CsA) or tacrolimus is associated with numerous side effects. One of the main reasons for restricting usage of CsA is hypertension. In tacrolimus treated subjects the frequency of these phenomena is significantly lower. The known molecular mechanism of action of tacrolimus and cyclosporine-A seems to be the same, thus we decided to compare modulatory effect of drugs on vascular smooth muscle contractility. Experiments were performed on isolated and perfused tail artery of Wistar rats. Contraction force was measured by increased degree of perfusion pressure with a constant flow rate. Concentration-response curves for agonist in the presence CsA were significantly shifted to the left with increase in maximal responses. This effect was due to increased calcium influx from extracellular calcium stores whereas there were no significant changes in calcium influx in the presence of tacrolimus; concentration-response curve was comparable to controls. Our results strongly support the idea that main difference between effects on smooth muscle contractility of calcineurin-dependent immunosuppressants: CsA and tacrolimus is related to the different level of extracellular calcium influx to the cytoplasm. The elucidation of these mechanisms may permit the identification of new therapeutic strategies against CsA-induced hypertension.

Effect of phospholipase C inhibition on vascular smooth muscle contraction

Phospholipase C is the key enzyme responsible for the hydrolysis of membrane phospholipids phosphatidylinositol 4,5-bisphosphate (PIP 2 ) to two intracellular transmitters - diacylglycerol (DAG) and inositol triphosphate (IP 3 ). PLC activation of smooth muscle leads to an increase in the concentration of IP 3 and DAG which initiates the increase in the concentration of calcium ions into the cytoplasm as a result of the flow from the intracellular and then from extracellular pool. Main aim of this study was to evaluate the effect of PLC inhibitor U-73122 on vascular smooth muscle contraction stimulated pharmacologically with phenylephrine (PHE, α 1 -adrenoceptor agonist) and arg-vasopressin (AVP, vasopressin receptor agonist). Material and methods. Experiments were performed on isolated and perfused tail artery of Wistar rats. Contraction force in our model was measured by increased level of perfusion pressure with a constant flow. Results. Reactivity of vascular smooth muscle cells to PHE (10 -9 - 10 -3 M/L), and AVP (10 -10 – 10 -4 M/L), in the control group and in the presence of U-73122 – phospholipase C inhibitor at concentrations 1, 3 and 10 μM/l was analyzed. EC 50 values calculated for PHE and AVP were 7.52 (±0.97) x10 -8 M/L and 1.84 (±0.6) x10 -8 M/L, respectively. The concentration-response curves obtained for PHE and AVP in the presence of U-73122 were shifted to the rightward with a decrease in maximal responses. In the presence of U-73122 the significant and dose dependent reduction in perfusion pressure was found for both agonists for calcium influx from intracellular calcium stores and from extracellular space. Conclusion. Results of our experiments suggest that in the presence of phospholipase C inhibitors, contraction induced by G-protein coupled receptors activation may by effectively inhibited by reduction in calcium influx from intra and extracellular calcium stores.

Modulatory effect of sodium nitroprusside and 8Br-cGMP on mastoparan-7 induced contraction

I n t r o d u c t i o n . Mastoparan-7 activates G-protein and stimulates apoptosis, but in smooth muscle cells leads to increase in perfusion pressure. Main a i m of this study was to evaluate the modulatory effect of 8Br-cGMP and sodium nitroprusside on vascular smooth muscle contraction induced by direct stimulation of G-protein with mastoparan-7. Ma t e r i a l a n d m e t h o d s . Experiments were performed on isolated and perfused tail artery of Wistar rats. Contraction force in our model was measured by increased level of perfusion pressure with a constant flow. R e s u l t s . Concentration-response curves obtained for mastoparan-7 presented an sigmoidal relation. In presence of SNP and 8Br-cGMP the significant and dose dependent leftward shift with significant reduction in maximal responses was present. Moreover, analyzing function of calcium stores the significant inhibition of influx from both, intra- and extracellular calcium stores was present. C o n c l u s i o n . Results of our experiments suggest that contraction induced by direct activation of G-protein with mastoparan-7 may by effectively inhibited in the presence of donors of nitric oxide such as sodium nitroprusside and in the presence of 8Br-cGMP.

Direct regulation of vascular smooth muscle contraction by mastoparan-7

Mastoparan-7 (mas-7) is a basic tetradecapeptide isolated from wasp venom, which activates guanine nucleotide-binding regulatory proteins (G-proteins) and stimulates apoptosis. In smooth muscle cells, mas-7 leads to an increase in the perfusion pressure. The main aim of this study was to evaluate the physiological effect of the direct stimulation of G-proteins in comparison to the typical stimulation of receptors in vascular smooth muscle cells (VSMCs). Experiments were performed on the isolated and perfused tail artery of Wistar rats. The contraction force in our model was measured by an increased level of perfusion pressure with a constant flow. The concentration response curves (CRCs) obtained for mas-7 were sigmoidal. In comparison to the curves for phenylephrine and vasopressin, the mas-7 curve was significantly shifted to the right with a significant reduction in maximal response. Mas-7 significantly increased the perfusion pressure for the intra- and extracellular calcium (Ca2+) influx to the cytoplasm. The presence of the pertussis toxin (PT) did not affect the mas-7-induced contraction. In comparison to phenylephrine and vasopressin, all the values of perfusion pressure following stimulation of the G-proteins by mas-7 were significantly lower. The results of our experiments suggested that mas-7 significantly induces the contraction of VSMCs. The binding site for mas-7 is different from that for PT; thus, PT does not affect VSMC contraction. The tissue effect of this stimulation is comparable to the stimulatory effect of partial agonists. Current knowledge regarding the apoptosis pathway reveals the significance of Ca2+ ions involved in this process. Therefore, mas-7 may induce apoptosis through an increase in the cytoplasmic Ca2+ concentration; however, the use of this mechanism in anticancer therapy must be preceded by a molecule modification that eliminates the vasoconstrictive effect.

Imidazole-induced contractility of vascular smooth muscle cells in the presence of U-73122, ODQ, indomethacin and 7-nitroindazole

The aim of the study was to assess the impact of modulating factors on vascular smooth muscle cells reactivity. Vascular resistance was induced by the administration of increasing concentrations of imidazole. The experiments were performed on isolated and perfused tail artery of Wistar rats (weight 250 g - 350 g). Rats were been narcotized by urethane (intraperitoneal injection) at a dose of 120 mg/kg, stunned and then sacrificed by cervical dislocation. In the following investigation classical pharmacometric methods were used. Relationships between concentration-response curves (CRCs) for imidazole observed in the presence of ODQ [(1H-(1,2,4)oxadiazolo-[4,3-a]quinoxalin-1-one)], 7-nitroindazole and indomethacin were analyzed. Imidazole-induced contractility of vascular smooth muscle cells was independent from alpha-adrenergic receptors and PLC activity. Reactivity of VSMCsinduced by imidazole, was significantly changed in the presence of ODQ and 7-nitroindazole.

Calcium blockers inhibit cyclosporine A-induced hyperreactivity of vascular smooth muscle cells

Cyclosporine belongs to the group of the most commonly used immunosuppressants. Hypertension occurs in approximately 30% of patients treated with this drug. However, the pathogenesis of this occurrence has not been explained to date. The purpose of our study was to clarify the mechanisms leading to the evolution of hypertension induced by cyclosporine A (CsA). We examined the changes in transmission within receptors and around the receptors. We also aimed to elucidate the mechanisms responsible for averting arterial hyperresponsiveness induced by the drug. Experiments were performed on isolated and perfused tail arteries of Wistar rats. Tissues surrounding the artery were removed and the proximal segment (length of 2-3 cm) was used for cannulation. Cannulated arteries were placed in a 20-ml glass chamber (vertical position). The contraction force in our model was measured by an increased degree of perfusion pressure with a constant flow rate (approximately 1 ml/min). The results showed that in the presence of CsA, the concentration-response curves/phenylephrine (PHE) curve shifted to the left. Cyclosporine increased the reactivity of the arteries to PHE. This effect was directly linked to the increase in the receptor reserve. The analysis of the reactivity of vascular smooth muscle showed that CsA increased the influx of calcium ions from the extracellular to the intracellular area. No difference was found between the contraction triggered by Bay-K8644 in the presence of CsA and the control probe. The increase in perfusion pressure induced by CsA was blocked by L-type calcium channel blockers (nifidipine and diltiazem). The results from our experiments show that CsA increases the reactivity of vessels to the effect of catecholamines. CsA also enhances signal transmission between G-protein coupled receptors (GPCRs) and calcium channels. The activation of protein kinase C also plays a significant role in this process. Our results suggest that the best choice for the pharmacotherapy of hypertension induced by CsA would be calcium channel antagonists.

Nitric oxide-releasing aspirin inhibits vasoconstriction in perfused tail artery of normotensive and spontaneously hypertensive rats

The aim of this study was to investigate the capacity of the 2-(acetyloxy)benzoic acid 3-(nitrooxymethyl)phenyl ester (NCX 4016), a nitric oxide (NO)-releaser derivative of aspirin, to decrease blood pressure in spontaneously hypertensive rats (SHR) and to counteract the adrenergic vasoconstriction in perfused tail artery of these animals. Oral treatment for 10 consecutive days with NCX 4016 (100 μmol/kg) in SHR and their genetic controls Wistar Kyoto (WKY) rats resulted in a reduction of blood pressure in SHR but not in WKY rats. In SHR, the NCX 4016 treatment increased the serum nitrite/nitrate and diminished the serum thromboxane B 2, whereas aspirin did not change blood pressure but abolished the serum thromboxane B 2. Perfused tail arteries excised from vehicle-treated SHR exhibited a significant impairment of endothelium-dependent vasorelaxant function. These vessels, prepared from SHR or WKY rats treated orally with NCX 4016 (10, 30 and 100 μmol/kg for 7 consecutive days), revealed a dose-dependent decrease in vasoconstriction in response to transmural nerve stimulation and norepinephrine, whereas aspirin was ineffective. Furthermore, in tail arteries of both SHR and WKY rats treated orally with NCX 4016 (100 μmol/kg for 7 consecutive days), the cGMP increased significantly. In conclusion, NCX 4016, by releasing NO and increasing cGMP in vascular tissue, reduces sympathetic-mediated vasoconstriction in resistance vessels and lowers blood pressure in SHR.

Ouabain changes arterial blood pressure and vascular reactivity to phenylephrine in L-NAME-induced hypertension.

Ouabain is an endogenous compound that has been associated with the genesis and maintenance of hypertension. This compound inhibits the Na+ pump activity, which leads to an accumulation of intracellular Na and ultimately might increase vascular tone. In nanomolar concentrations, it enhances vasopressor responses to phenylephrine in some vascular beds from normotensive and hypertensive rats. However, it is not known whether this action of ouabain is a common mechanism for all models of hypertension. The aim of this work was to determine whether ouabain can alter pressor responses to phenylephrine in rats with Nomega-nitro-l-arginine methyl ester (L-NAME)-induced hypertension. In anesthetized rats, ouabain (0.18 microg/kg, i.v.) increased arterial blood pressure in L-NAME-treated rats but not in controls. Ganglionic blockade by hexamethonium (5 mg/kg, i.v.) prevented the increase in arterial blood pressure produced by ouabain in L-NAME-treated rats. Additional studies using isolated perfused tail artery preparations were performed to investigate which factors are involved in the action of ouabain in L-NAME-treated rats. The effects of 10 nM ouabain on the vasoconstrictor actions of phenylephrine were determined on preparations with intact or damaged endothelium or in the presence of tetraethylammonium (a K+-channel blocker). Ouabain reduced pressor actions of phenylephrine in preparations with an intact endothelium. However, after endothelial damage or infusing tetraethylammonium, the response to phenylephrine was increased after ouabain. In tails from L-NAME-treated rats, the functional activity of the Na, K+-ATPase was reduced, and 10 nM ouabain did not produce any further reduction. In conclusion, in this model of hypertension, a low dose of ouabain (0.18 microg/kg) increased arterial blood pressure in vivo probably as a result of increased sympathetic tone. However, this effect was not accompanied by an enhanced action of phenylephrine on the tail vascular bed with an intact endothelium. The results suggest that this was due to the release of an endothelium-derived K+-channel opener.

Effects of chronic and acute aminoguanidine treatment on tail artery vasomotion in ageing rats.

1. This study was designed to evaluate the effects of aminoguanidine, a selective inhibitor of the inducible isoform of nitric oxide synthase (iNOS), on the reactivity and intracellular calcium ([Ca(2+)](i)) mobilization induced by noradrenaline in the perfused tail artery from aged WAG/Rij rats. Global mean internal diameter was 350+/-15 microns and wall thickness 161+/-3 microns. The influence of the endothelium on these responses was also analysed. The intracellular dye fura-2 for [Ca(2+)](i) measurements was used. 2. Noradrenaline-induced vasoconstriction decreased progressively from 3 to 20 and 30 months. Removal of the endothelium attenuated vasoconstriction in 20 and 30 month-old rats (P<0.05) but not in young rats. 3. Chronic administration of aminoguanidine (50 mg kg(-1) day(-1), p.o.) to WAG/Rij rats from 20 to 30 months enhanced (P<0. 01) the [Ca(2+)](i)-sensitivity of noradrenaline-induced vasoconstriction. 4. Aminoguanidine (300 microM) in vitro significantly shifted the concentration-vasoconstriction curve to noradrenaline to the left (P<0.01) in denuded vessels from both 20 and 30 month-old rats. The acute inhibitory effect of aminoguanidine was also observed after chronic aminoguanidine treatment. Aminoguanidine failed to modify vasoconstriction in the presence of the endothelium. 5. Acute aminoguanidine (300 microM) treatment did not modify vasoconstriction induced by noradrenaline in young rats. 6. Quantification of iNOS mRNA expression in tail arteries from 3 and 20 month-old WAG/Rij rats showed that expression was enhanced (x2.1, P<0.01) with age. 7. These results suggest that an inflammatory process develops in the media of the rat tail artery with age and that the subsequent increase in non-endothelial iNOS activity attenuates noradrenaline-induced vasoconstriction.

Active Immunization Against Endothelin-1 is Associated With a Decrease in Plasma Endothelin-1 and Changes in Vascular Reactivity

Summary: Exogenous endothelin-1 (ET-1) or high concentrations of the peptide in pathological conditions have marked effects on vascular reactivity. In order to evaluate the role of endogenous ET-1 we investigated responsiveness of conduit (aorta) and of resistant-like (tail artery) vessels in ET-1-deficient rats. Elimination of circulating ET-1 was achieved by active immunization of Wistar rats with a peptide-haemocyanin conjugate (anti-ET-1 group), leading to a marked reduction in plasma level of the peptide in comparison with that of vehicle-treated animals (control group): 1.9 fmol/ml vs 4.9 fmol/ml, respectively. The immunization was associated with a slight elevation of mean arterial pressure, whereas heart rate remained unchanged. In the anti-ET-1 group rings of isolated aorta displayed reduced sensitivity to ET-1: EC50 = 6.57 nM vs 2.95 nM in the control group. Tail arteries of the ET-1-deficient rats showed diminished responses to ET-1, the maximal rise in perfusion pressure: +5.2 mmHg vs +13.6 mmHg in the control group. After immunization, rings of isolated aorta displayed no changes in endothelium-dependent relaxation to acetylcholine (Ach, EC50 = 0.20 μM vs 0.35 μM in the control group), whereas experiments on perfused tail artery showed a twofold reduction in Ach effects. Thus, depletion of circulating ET-1 induces slight changes in haemodynamics associated with altered vessel responsiveness to vasoactive substances.

Active immunization against endothelin-1 is associated with a decrease in plasma endothelin-1 and changes in vascular reactivity.

Exogenous endothelin-1 (ET-1) or high concentrations of the peptide in pathological conditions have marked effects on vascular reactivity. In order to evaluate the role of endogenous ET-1 we investigated responsiveness of conduit (aorta) and of resistant-like (tail artery) vessels in ET-1-deficient rats. Elimination of circulating ET-1 was achieved by active immunization of Wistar rats with a peptide-haemocyanin conjugate (anti-ET-1 group), leading to a marked reduction in plasma level of the peptide in comparison with that of vehicle-treated animals (control group): 1.9 fmol/ml vs 4.9 fmol/ml, respectively. The immunization was associated with a slight elevation of mean arterial pressure, whereas heart rate remained unchanged. In the anti-ET-1 group rings of isolated aorta displayed reduced sensitivity to ET-1: EC50 = 6.57 nM vs 2.95 nM in the control group. Tail arteries of the ET-1-deficient rats showed diminished responses to ET-1, the maximal rise in perfusion pressure: +5.2 mmHg vs +13.6 mmHg in the control group. After immunization, rings of isolated aorta displayed no changes in endothelium-dependent relaxation to acetylcholine (Ach, EC50 = 0.20 microM vs 0.35 microM in the control group), whereas experiments on perfused tail artery showed a twofold reduction in Ach effects. Thus, depletion of circulating ET-1 induces slight changes in haemodynamics associated with altered vessel responsiveness to vasoactive substances.

Effect of angiotensin II receptor blockade on the interaction between enalaprilat and doxazosin in rat tail arteries.

1. Previous work has shown that enalaprilat, an inhibitor of angiotensin-converting enzyme (ACE), potentiated the actions of alpha 1-adrenoceptor antagonists; it was hypothesized that angiotensin II (AngII) modulated the activity of alpha 1-adrenoceptors. This hypothesis was tested in Sprague-Dawley rat isolated perfused tail arteries using the AT1 receptor antagonist losartan and the AT2 receptor antagonist PD123319. 2. Losartan had no alpha 1-adrenoceptor antagonist effects at concentrations below 1 mumol/L. Similarly, losartan (0.1 mumol/L) had no effect on the alpha 1-adrenoceptor antagonist action of doxazosin (1, 10 nmol/L) nor on the potentiation of doxazosin by enalaprilat (1 mumol/L). 3. PD123319 (0.1 mumol/L) had no alpha 1-adrenoceptor antagonist effect but altered the mode of action of the alpha 1-adrenoceptor antagonist doxazosin: PD123319 changed doxazosin from a competitive to a non-competitive antagonist, as evidenced by the reduced slope of the dose-response curve for the alpha 1-adrenoceptor agonist phenylephrine. 4. These results suggest that AngII can modulate alpha 1-adrenoceptor function in rat tail arteries via an indirect action at AT2 receptors. However, the present results do not rule out the involvement of bradykinin, endothelin or prostaglandin in the modulation of alpha 1-adrenoceptor function by angiotensin II.

Vascular and cardiac effects of DV-7028, a selective, 5-HT2-receptor antagonist in rats.

The effect of 5HT2A-receptor antagonist DV-7028 (3-[2-[4-(4-fluorobenzoyl)piperidin-1-yl]ethyl]-6,7,8,9-tetrahydro - 2H-pyrido[1,2,-a]-1,3,5-triazine-2,4(3H)-dione maleate on the rat cardiovascular system was evaluated. DV-7028 (0.1 and 1.0 mg/kg), given intravenously, caused a significant, dose-dependent decrease in mean arterial blood pressure in anesthetized normotensive rats. In vagotomized rats, administration of DV-7028 resulted in a reduction of mean blood pressure, but this effect was less prominent than that seen in nonvagotomized rats. Intravenous administration of DV-7028 induced bradycardia, which was almost completely abolished by vagotomy. In pithed rats, bradycardia and hypotension were not demonstrated after DV-7028 administration. In pithed rats, serotonin administered intravenously caused a dose-dependent increase in blood pressure. In this experimental model, DV-7028 inhibited the pressor effects of serotonin at doses of 0.01 and 0.1 mg/kg, which caused neither hypotension nor bradycardia in anesthetized rats. DV-7028 strongly inhibited the pressor effects of serotonin in the isolated perfused hindlegs of the rat (IC50 = 0.032 +/- 0.004 microM) and caused a concentration-dependent, almost parallel shift to the right of the concentration-response curve to serotonin for its pressor effect in the rat perfused tail artery (pA2 value for DV-7028 was 7.92, a slope 0.94). These data demonstrate that DV-7028 exhibits 5-HT2A-receptor antagonistic property in the rat cardiovascular system. Besides this peripheral action, DV-7028, when applied in high doses, exerts hypotension and bradycardia via an unknown site and mechanism.