The role of Rho-kinase and calcium ions in constriction triggered by ET-1.

Endothelin-1 (ET-1) is one of the key factors regulating tension of smooth muscles in blood vessels. It is believed that ET-1 plays an important role in pathogenesis of hypertension, and cardiovascular diseases; therefore, research in order to limit ET-1-mediated action is still in progress. The main objective of this paper was to evaluate the role of Rho-kinase in the ET-1-induced constriction of arteries. The analysis also included significance of intra- and extracellular pool of calcium ions in constriction triggered by ET-1. The studies were performed on perfused Wistar rat tail arteries. Concentration response curve (CRC) was determined for ET-1 in the presence of increased concentrations of Rho-kinase inhibitor (Y-27632) and IP3-receptor antagonist (2APB), both in reference to constriction triggered by solely ET-1. Afterwards, the influence of calcium ions present in the perfusion fluid was evaluated in terms of the effect triggered by 2APB and occurring in arteries constricted by ET-1. ET-1, in concentration dependent manner, leads to increase in perfusion pressure. Y-27632 and 2APB lead to shift of the concentration response curve for ET-1 to the right with simultaneously lowered maximum effect. There was no difference in reaction of the artery constricted by ET-1 and treated with 2APB in solution containing calcium and in calcium-free solution. Vasoconstrictive action of endothelin is not significantly dependent on the inflow of extracellular calcium, but it is proportional to inflow of Ca2+ related to activation of IP3 receptors and to Rho-kinase activity.

Therapeutic drug monitoring of digoxin-20 years of experience.

BACKGROUND: Digoxin is the oldest drug used in the pharmacotherapy of heart failure (HF). However, digoxin remains an important therapeutic option for patients with persistent symptoms of HF occurring despite the implementation of standard pharmacotherapy. Digoxin concentration serum (SCD) should equal 1-2ng/ml. The aim of our study was to measure of SCD among the hospitalized patients as well as to determine the selected factors influencing the concentration of the digoxin in the blood. METHODS: The presented research was based on a retrospective analysis including 2149 patients treated with digoxin and hospitalized between 1980 and 2000. Was used for the determination of SCD automatic analyzer TDX ABBOTT GmbH - fluorescence polarization immunoassay (FPIA), with therapeutic range for digoxin of 0.8-2.0ng/ml. RESULTS: Average SCD result in the study population was located within the therapeutic range and amounted 1.06ng/ml (55.7% of patients). Statistically significant differences in digoxin level were observed depending on the way of medicine administration (p=0.000001) and the daily amount (p=0.001). Moreover, statistically significant differences in digoxin level were observed depending on sex (p=0.00002). CONCLUSIONS: An elevated level of digoxin was observed in the case of patients who received the medication both orally and intravenously, together with an increase in the daily amount of digoxin doses. It was confirmed that an elevated digoxin level occurs in the course of treatment in the case of women.

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.

Evaluation of VCAM-1 and ICAM-1 concentration and values of global tests concerning the coagulation system of patients suffering from subarachnoid haemorrage.

INTRODUCTION: The term 'subarachnoid haemorrhage' (SAH) stands for bleeding into the subarachnoid space, regardless of its source. It may be of primary character when the source of bleeding is situated within the subarachnoid space. Subarachnoid haemorrhage is often described as spontaneous bleeding, mainly in order to differentiate it from post-traumatic bleeding. OBJECTIVE: The aim of the study was to evaluate the concentration of ICAM-1 and VCAM-1 in the blood of patients in the early phase following subarachnoid haemorrhage in terms of searching for markers useful in subarachnoid bleeding diagnostics and monitoring a patient's clinical state. MATERIALS AND METHOD: The study comprised 85 patients (47 women, 38 men), aged 29-81 (average 53±12 years), suffering from subarachnoid haemorrhage. The control group comprised 45 healthy people selected according to gender and age corresponding with the experimental group. RESULTS: The study revealed that the concentration of ICAM-1 and VCAM-1 was significantly higher in patients suffering from subarachnoid haemorrhage. Additionally, the concentration of fibrinogen decreased, aPTT was shorter and the concentration of D-dimers increased. The studied parameters did not differ with respect to the age or gender of the patients. It was stated that according to the Hunt and Hess scale, the concentration of ICAM-1 was considerably higher in the group of patients in the most severe neurological state, compared to other patients. It was also observed that the concentration of fibrinogen was significantly higher, aPTT was shorter, and the concentration of D-dimers increased in the afore-mentioned group. CONCLUSIONS: Evaluation of the concentration of adhesion molecules, as well as values of global tests concerning the coagulation system, may serve as a useful diagnostic tool for SAH.

The Modulatory Effect of Ischemia and Reperfusion on Arginine Vasopressin-Induced Arterial Reactions.

Aim of the Study. The purpose of this study was to investigate the impact of ischemia and reperfusion on the resistance of arteries to AVP (arginine vasopressin), with a particular emphasis on the role of smooth muscle cells in the action of vasopressin receptors and the role of the cGMP-associated signalling pathway. Materials and Methods. Experiment was performed on the perfunded tail arteries from male Wistar rats. The constriction triggered by AVP after 30 minutes of ischemia and 30 and 90 minutes of reperfusion was analysed. Analogous experiments were also carried out in the presence of 8Br-cGMP. Results. Ischemia reduces and reperfusion increases in a time-dependent manner the arterial reaction to AVP. The presence of 8Br-cGMP causes a significant decrease of arterial reactivity under study conditions. Conclusions. Ischemia and reperfusion modulate arterial contraction triggered by AVP. The effect of 8Br-cGMP on reactions, induced by AVP after ischemia and reperfusion, indicates that signalling pathway associated with nitric oxide (NO) and cGMP regulates the tension of the vascular smooth muscle cells.

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.

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Rho-kinase inhibitor reduces hypersensitivity to ANG II in human mesenteric arteries retrieved and conserved under the same conditions as transplanted organs.

Rho-kinase and GTP-ase Rho are important regulators of vascular tone and blood pressure. The aim of this study was to investigate the role of Rho-kinase in artery reactions induced by angiotensin II (ANG II) and the effects of ischemia-reperfusion injury as well as the function of intra- and extracellular calcium in these reactions. Experiments were performed on mesenteric superior arteries procured from cadaveric organ donors and conserved under the same conditions as transplanted kidneys. The vascular contraction in reaction to ANG II was measured in the presence of Rho-kinase inhibitor Y-27632, after ischemia and reperfusion, in Ca2+ and Ca2+-free solution. The maximal response to ANG II was reduced after ischemia, while an increase was observed after reperfusion. Vascular contraction induced by ANG II was decreased by Y-27632. Y-27632 reduced vascular contraction after reperfusion, both in Ca2+ and Ca2+-free solution. Reperfusion augments vascular contraction in reaction to ANG II. The Rho-kinase inhibitor Y-27632 reduces the hypersensitivity to ANG II after reperfusion mediated by both intra- and extracellular calcium. These results confirm the role of Rho-kinase in receptor-independent function of ANG II and in reperfusion-induced hypersensitivity.

Effect of pertussis toxin on calcium influx in three contraction models.

Pertussis toxin (PTX) blocks G protein activation and inhibits signal transmission from the activated receptor to effectors that are specific for the G protein-coupled receptor. The aim of the present study was to evaluate the effect of PTX on vascular smooth muscle cells that were stimulated pharmacologically with phenylephrine (α-adrenoceptor agonist), mastoparan-7 (direct G-protein activator) and Bay K8644 (direct calcium channel activator). The changes in perfusion pressure that were proportional to the degree of phenylephrine-induced constriction of rat tail arteries were assessed. Concentration-response curves (CRCs) that were obtained for phenylephrine, mastoparan-7 and Bay K8644 presented a sigmoidal association. A significantly reduced calcium influx to the cytoplasm in the presence of mastoparan-7 resulted in a significant rightward shift of the CRCs with a significant reduction in maximal responses. The presence of PTX did not change mastoparan-7 and Bay K8644-induced contraction, whereas the significant inhibition of phenylephrine-induced contraction was found. The results of the experiments indicated that PTX significantly inhibited phenylephrine-induced contraction of vascular smooth muscle cells by inhibition of calcium influx from the intra- and extracellular calcium space. PTX did not change the smooth muscle contraction that was induced by mastoparan-7 and Bay K8644. The predominant effect of mastoparan-7 may be associated with other binding sites as compared to the G-protein or PTX may bind to other sites than mastoparan-7.

Influence of celecoxib on the vasodilating properties of human mesenteric arteries constricted with endothelin-1.

The mitogenic and vasoconstrictive properties of the vascular system are attributed to endothelin-1 (ET-1). ET-1 serum concentration increases in a number of pathological conditions, particularly in those associated with blood vessel constriction. ET-1 is also associated with the underlying pathomechanisms of primary pulmonary hypertension, arterial hypertension and eclampsia. The aim of this study was to compare the vasodilating properties of selected phosphodiesterase (PDE) inhibitors and celecoxib in human mesenteric arteries constricted with ET-1, and investigate the role of the endothelium in relaxation. Perfused human mesenteric arteries were collected and stored under the same conditions as organs for transplantation. The mesenteric arteries (with and without the endothelium) were constricted by the addition of ET-1 and treated with one of the following: sildenafil (PDE5 inhibitor), zaprinast (PDE5 and 6 inhibitor), rolipram (PDE4 inhibitor) and celecoxib [cyclooxygenase-2 (COX-2) inhibitor]. Based on the observed changes of the perfusion pressure, concentration response curves (CRCs) were prepared for the respective inhibitors and the EC50 (concentration causing an effect equal to half of the maximum effect), pD2 (negative common logarithm of EC50) and relative potency (RP) were calculated. The results suggested that all the inhibitors triggered a concentration-dependent decrease in the perfusion pressure in isolated human superior mesenteric arteries with endothelium constricted by the addition of ET-1. In the arteries without endothelium, CRCs for celecoxib and rolipram were shifted to the right without a significant decrease in the maximum dilating effect. Moreover, CRCs for sildenafil and zaprinast were shifted to the right with a simultaneous significant decrease in the maximum dilating effect and with an increased inclination angle in reference to the concentration axis. In the presence of the endothelium, all of the evaluated PDE inhibitors, as well as celecoxib, reduced the reactivity of the mesenteric arteries caused by ET-1. Sildenafil indicated the lowest efficacy in the presence of the endothelium, but showed a higher potency compared to that of the other compounds. Removing the endothelium significantly reduced the vasodilating efficacy of PDE5 and 6 inhibitors and a statistically significant influence on the vasodilating efficacy of PDE4 inhibitor and celecoxib was observed. The high vasorelaxing efficacy of celecoxib at the background of the PDE inhibitors was observed, not only in the presence, but also in the absence of the endothelium and may be evidence for the relaxation induced by this COX-2 inhibitor in the cAMP- and cGMP-dependent pathways.

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.

Role of endothelium, acetylocholine and calcium ions in Bay K8644- and KCl-induced contraction.

The aim of this study was to establish the involvement of acetylcholine (Ach) and calcium ions in modulating contractions induced by Bay K8644 (an agonist of calcium channels located in the cell membrane) and KCl (at depolarizing concentrations), and also to examine the importance of the vascular endothelium in the activity of Bay K8644. The study was performed on perfused Wistar rat tail arteries. Contraction induced by Bay K8644 with the participation of intracellular (in calcium­free physiological salt solution, FPSS) and extracellular (in physiological salt solution, PSS, following the emptying of the cellular Ca2+ stores) pools of Ca2+ and the addition of nitro-L-arginine (L­NNA; nitric oxide synthase inhibitor) or 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (ODQ; an inhibitor of soluble guanylyl cyclase) was studied. In addition, the effect of Ach on the contraction response was analyzed and the results were compared with the depolarizing action of KCl. The effects of 8Br­cGMP on the artery contraction induced by Bay K8644 prior to and following removal of the endothelium were compared. Bay K8644 and KCl in PSS induced vascular contraction, which was reduced with the addition of Ach. The spasmolytic Ach action did not occur in the presence of L­NNA and ODQ. 8Br­cGMP reduced the contraction of arterial walls (with and without endothelium) induced by Bay K8644. The increase in vascular tone induced by Bay K8644 and KCl was independent of the intracellular calcium ion pool. The relaxant effect of Ach on the responses stimulated by Bay K8644 and KCl indicated the participation of nitric oxide in modulating the reactivity of the arteries to the factors examined, resulting in an influx of Ca2+ into the cell.

Role of nitric oxide and cGMP in the modulation of vascular contraction induced by angiotensin II and Bay K8644 during ischemia/reperfusion.

Vascular smooth muscle tone changes under the influence of numerous contracting and relaxing factors. The purpose of the present study was to determine the modulating effect of ischemia and reperfusion (I/R) on contraction triggered by angiotensin II (ANG II) and Bay K8644 as well as to investigate the importance of nitric oxide (NO) and cGMP in these reactions. Experiments were performed on isolated and perfused Wistar rat tail arteries. The contraction triggered by ANG II and Bay K8644 with the use of intracellular (in calcium-free physiological salt solution; FPSS) and extracellular (in physiological salt solution; PSS) pools of calcium ions after I/R and in the presence of sodium nitroprusside (SNP), (8)Br-cGMP, an endothelial NO synthase (NOSe) inhibitor (L-NG-nitroarginine methyl ester; L-NAME) or ODQ [an inhibitor of soluble guanylyl cyclase (GC)] was evaluated. ANG II triggered contraction in FPSS and PSS, but Bay K8644 only in PSS. Ischemia reduced and reperfusion intensified the response of the artery to ANG II, but did not change the action of Bay K8644. SNP and (8)Br-cGMP reduced the response of the vessels to ANG II and did not change the modulating effect of ischemia, but reduced the intensifying action of reperfusion on contraction caused by the presence of ANG II. SNP lowered the action of Bay K8644 in PSS. In PSS, L-NAME and ODQ intensified the action of ANG II, eliminating the reducing effect of ischemia on the contraction caused by ANG II, but did not influence the intensifying reaction caused by reperfusion. L-NAME and ODQ did not influence the action of Bay K8644. I/R modulated the contraction of arteries triggered by ANG II, but did not influence the response to Bay K8644. The intra- and extracellular pools of calcium ions mediate the action of ANG II, but Bay K8644 stimulated contraction only with participation of calcium ions flowing into the cell. Control of the vascular smooth muscle tone associated with the action of NO and cGMP is subject to modulation under conditions of I/R.

Role of acetylcholine and calcium ions in three vascular contraction models: Angiotensin II, phenylephrine and caffeine.

The aim of this study was to determine the role of acetylcholine and calcium ions in modulating the vascular contraction induced by angiotensin II (ANG II), phenylephrine (PHE) and caffeine. The study was performed on perfunded Wistar rat tail arteries. The contraction caused by ANG II, PHE and caffeine with the participation of intracellular [in free physiological salt solution (FPSS)] and extracellular [in physiological salt solution (PSS), after emptying the cellular stores] pools of calcium ions and the addition of L-NNA (NOSe inhibitor) or ODQ (GC inhibitor) was studied. Then the effect of acetylcholine on the contraction responses was analyzed. ANG II, PHE and caffeine induced an increase in perfusion pressure in PSS and FPSS. Acetylcholine reduced the contraction resulting from the presence of ANG II and PHE, but not caffeine. L-NNA and ODQ abolished the spasmolytic action of acetylcholine. Both pools of calcium ions mediated the action of ANG II and PHE, and caffeine induced the contraction with the participation of calcium released from intracellular stores. The spasmolytic effect of acetylcholine on responses stimulated by ANG II and PHE indicates the participation of nitric oxide in modulating the reactivity of the arteries on the studied agonists of the metabotropic receptors. No observed acetylcholine effect on caffeine suggests that the pathway associated with nitric oxide does not interfere with the contraction induced by the ryanodin receptor.

Role of calcium and calmodulin in reaction of gastric fundus contraction.

BACKGROUND: The subject of this study is determination of the influence of calmodulin and calcium on gastric fundus smooth muscle contraction. During experiments, the author tested the influence of a serotonin receptor agonist, serotonin (5-HT), causing smooth muscle contraction. MATERIAL/METHODS: Testing was conducted on tissues isolated from rat's stomach. Male Wistar rats with weight between 220 g and 360 g were anesthetized by intraperitoneal injection of urethane (120 mg/kg). The stomach was dissected, and later the gastric fundus was isolated. Tissue was placed in a dish for insulated organs with 20 ml in capacity, filled with Krebs fluid. Results contained in the study are average values ± SE. In order to determine statistical significance, the principles of receptor theory were used (Kenakin modification). RESULTS: According to conducted tests, we can deduce that 8 Br cGMP stops the reaction of gastric fundus smooth muscle contraction induced by serotonin. The use of 8Br-cGMP in the range of concentrations between 10 and 300 µM leads to reduction of maximum effect from 100% to 46%. Similar changes were obtained after the use of guanylate cyclase activator (CG) - YC-1. Curves for the contractile activity of serotonin along with an increase of concentration YC-1 are shifted to the right, and the maximum effect of reaction decreases. Increasing concentrations of flunarizine, a calmodulin antagonist, in a concentration-dependent way blocks binding between calcium and calmodulin, and at the same time leads to the shift of concentration-effect curves for serotonin to the right and a decrease of maximum reaction. Increasing concentrations of ODQ, a guanylate cyclase inhibitor lead to statistically significant shift of the curves to the left, decrease of EC(50) value and simultaneous increase of maximum reaction to serotonin. CONCLUSIONS: According to conducted testing, serotonin causes gastric fundus smooth muscle contraction dependent on concentration. Reaction of contraction induced by serotonin is stopped by a calmodulin antagonist, flunarizine. In addition, experiments confirmed participation of cyclical nucleotides in blocking reaction of gastric fundus contraction.

Role of M1 receptor in regulation of gastric fundus smooth muscle contraction.

BACKGROUND: The subject of this study is determination of the influence of drugs on gastric fundus smooth muscle contraction induced by activation of muscarinic receptors M1. Experiments tested interactions between a receptor agonist, carbachol and muscarinic receptor antagonists, atropine and pirenzepine. MATERIAL/METHODS: Testing was conducted on tissues isolated from rat's stomach. Male Wistar rats with weight between 220 g and 360 g were anesthetized by intraperitoneal injection of urethane (120 mg/kg). The stomach was dissected, and later the gastric fundus was isolated. Tissue was placed in a dish for insulated organs with 20 ml in capacity, filled with Krebs fluid. Results contained in the study are average values ± SE. In order to determine statistical significance, the principles of receptor theory were used (Kenakin modification). RESULTS: According to tests, carbachol, in concentrations ranging between 10(-8) M to 10(-4) M, in a dosage-dependent way induces gastric fundus smooth muscle contraction. Presented results indicate that carbachol meets the conditions posed to full agonists. On the other hand, atropine, a non-selective muscarinic receptor antagonist, causes a concentration-dependent shift of concentration-effect curve (for carbachol) to the right, maintaining maximum reaction. According to analysis of the curve determined, we can deduce that atropine meets the conditions posed to competitive antagonists. The use of pirenzepine, a competitive receptor agonist M1, causes shift of concentration-effect curve (for carbachol) to the right, maintaining maximum reaction. CONCLUSIONS: From the testing conducted on the preparation of the gastric fundus we can deduce that atropine causes shift of concentration-effect curves for carbachol to the right. A similar effect is released by pirenzepine, selectively blocking muscarinic receptors of M1 type. The results indicate that in the preparation of the gastric fundus smooth muscle, M1 type receptors occur also postsynaptically.

The role of the endothelium in the regulation of vascular smooth muscle cell contractions induced by angiotensin II after ischemia and reperfusion.

In this study, we investigated smooth muscle cell contractions induced by angiotensin II (ANG II) in blood vessels with or without endothelium after ischemia/reperfusion. Experiments were done on tail arteries, with or without endothelium, of perfused male Wistar rats. We analyzed the influence of ANG II on vascular contractions in the presence of sodium nitroprusside or 8Br-cGMP and after ischemia/reperfusion using classical pharmacometric methods. Vascular contractions induced by ANG II were decreased by sodium nitroprusside and 8BrcGMP. Reductions in maximal response and increases in EC(50) values after ischemia were observed only in vessels with endothelium. After reperfusion, increases in maximal response and decreases in EC(50) values were observed. Decreases in ANG II induced vascular contractions on caused by ischemia involves the presence of endothelium, synthesis of nitric oxide and activation of cGMP. The increase in the reaction to ANG II that is induced by reperfusion is independent of the endothelium.

The role of calcium in modulating the reactivity of the smooth muscle cells during ischemia/reperfusion. Part 1.

BACKGROUND: Calcium ions regulate the function of cells in many ways, acting as first messengers of intercellular information and second messengers of intracellular information. Changes in cytoplasmic calcium levels depend on calcium influx from the extracellular space or calcium release from cellular stores. Increase in calcium ion concentration takes place in pathological situations, such as ischemia. In the present study the roles of calcium and G protein in contraction induced by angiotensin II (agonist of the metabotropic receptor AT1), phenylephrine (agonist of alpha1-adrenergic metabotropic receptor), and Bay K8644 (a calcium channel agonist) after ischemia/reperfusion were investigated. MATERIAL/METHODS: Experiments were performed on perfused male Wistar rats' tail arteries. Contraction induced by angiotensin II, phenylephrine, and Bay K8644 mediated by intracellular or extracellular calcium after ischemia/reperfusion and in the presence of the blocker of G protein Bordetella pertussis toxin (P 7208) was analyzed. RESULTS: Ischemia reduced while reperfusion augmented the response of vascular smooth muscle cells to angiotensin II and phenylephrine, but they did not change the effects of Bay K8644. P 7208 decreased the effects of phenylephrine mediated by intracellular and extracellular calcium and reduced the reactions of angiotensin II mediated only by intracellular calcium, but did not change the effects of Bay K8644. CONCLUSIONS: Ischemia/reperfusion modulates vascular contraction induced by angiotensin II and phenylephrine. Both intracellular and extracellular calcium ions mediate the contraction induced by angiotensin II and phenylephrine. The results suggests that G protein modulates the effects of angiotensin II mediated by intracellular calcium ions while it plays a role in the reactions of phenylephrine mediated by calcium coming from both sources, intracellular and extracellular.

The role of calcium in modulating the reactivity of the smooth muscle cells during ischemia/reperfusion. Part 2.

BACKGROUND: Damage of transplanted organs during reperfusion is still a problem that prompts the search for new drugs able to diminish the risk of graft rejection. The aim of this study was to examine the influence of antioxidant system on the contraction of arteries induced by angiotensin II during ischemia/reperfusion and to determine the role of intracellular and extracellular calcium ions under these conditions. MATERIAL/METHODS: The experiments were performed on male Wistar rats' tail arteries. The effects of angiotensin II on vascular tone were examined after ischemia/reperfusion in the presence of catalase or aminotriazole. To determine the role of intracellular and extracellular Ca(2+), the experiments were performed in Ca(2+)-free PSS and PSS. RESULTS: Angiotensin II increased perfusion pressure in both Ca(2+)-free PSS and PSS. After ischemia, the reactions induced by angiotensin II were lower, while after reperfusion they were higher. In the presence of catalase the effects induced by angiotensin II were lower and in the presence of aminotriazole higher. CONCLUSIONS: Ischemia inhibits and reperfusion augments the perfusion pressure induced by angiotensin II. The results confirm the vasoprotective effect of catalase and the destructive influence of aminotriazole in modulating the reactions of vascular smooth muscle cells to ANG II after ischemia/reperfusion. These results suggest that the antioxidant system plays a role in modulating the reactions induced by angiotensin II after ischemia/reperfusion and that reperfusion disturbs the balance between antioxidants and the production of reactive oxygen species.