Viktor Bauer

Effect of N-acetylcysteine on colitis induced by acetic acid in rats.

(1) To verify the proposed role of reactive oxygen species (ROS) in ulcerative colitis, the effect of an antioxidant N-acetylcysteine (NAC) was studied in acetic acid (AA)-induced colonic inflammation. (2) Depending on the dose used, NAC administered intracolonically was found to reduce the extent of colonic damage, along with a decrease in myeloperoxidase (MPO) activity, colonic wet weight and wet/dry weight ratio. (3) NAC attenuated the enhanced vascular permeability and prevented the depletion of colonic reduced glutathione (GSH) caused by AA administration. (4) The findings indicate that NAC may prove beneficial in the treatment of colitis.

Reactive oxygen species induced smooth muscle responses in the intestine, vessels and airways and the effect of antioxidants

Numerous experimental data confirm the importance of reactive oxygen species (ROS) in physiological activities of smooth muscles and in the pathogenesis of various diseases with altered function of smooth muscles. The present study shows that smooth muscles of the intestine, airways and vessels, as well as their epithelium, endothelium and innervations, might be important targets of the ROS action. We demonstrated differences among the actions of various ROS (endogenous, exogenous, produced enzymatically, non-enzymatically) as well as among their actions in different smooth muscle tissues. Our results indicate that ROS are involved in changes in muscle tone, membrane conductance, calcium homeostasis, calcium-dependent processes, as well as in eicosanoid and nitric oxide metabolism. The effects of antioxidative enzymes (superoxide dismutase, catalase), of several drugs of natural origin (e.g. Kampo Medicines) and synthetic agents (e.g. stobadine, nitrosopine, ACE inhibitors) suggest that smooth muscle tissues are useful models to study ROS action and drug intervention in ROS induced injuries.

Effect of desensitization induced by adenosine 5'-triphosphate substance P, bradykinin, serotonin, γ-aminobutyric acid and endogenous noncholinergic-nonadrenergic transmitter in the guinea-pig ileum

The cholinergic and noncholinergic-nonadrenergic (NCNA) excitatory and inhibitory responses of the guinea-pig ileum to transmural nerve stimulation (TNS) were studied. Unlike the contraction induced by histamine and acetylcholine the responses to TNS, ATP, substance P, bradykinin, 5-HT and GABA were not sustained. The contraction and its fading during TNS involved the activation of cholinergic, adrenergic and NCNA neurons. Substance P, 5-HT and ATP desensitization resulted in reduction of the excitatory NCNA response whereas that due to bradykinin attenuated both the excitatory and inhibitory NCNA responses. The desensitization against TNS and the potential transmitters studies was selective except in the case of ATP. The present results suggest that it is unlikely that ATP, bradykinin or GABA would be the NCNA transmitters in the guinea-pig ileum. The cross-desensitization between the excitatory NCNA transmitter on the one hand, and substance P (markedly expressed) and 5-HT (slightly expressed) on the other hand, give further evidence in favor of the possible transmitter role of substance P-like peptide in excitatory NCNA transmission and of the role of 5-HT in the activation of NCNA neurons.

Protection of the vascular endothelium in experimental situations.

Protection of the vascular endothelium in experimental situations One of the factors proposed as mediators of vascular dysfunction observed in diabetes is the increased generation of reactive oxygen species (ROS). This provides support for the use of antioxidants as early and appropriate pharmacological intervention in the development of late diabetic complications. In streptozotocin (STZ)-induced diabetes in rats we observed endothelial dysfuction manifested by reduced endothelium-dependent response to acetylcholine of the superior mesenteric artery (SMA) and aorta, as well as by increased endothelaemia. Changes in endothelium-dependent relaxation of SMA were induced by injury of the nitric oxide radical (·NO)-signalling pathway since the endothelium-derived hyperpolarising factor (EDHF)-component of relaxation was not impaired by diabetes. The endothelial dysfunction was accompanied by decreased ·NO bioavailabity as a consequence of reduced activity of eNOS rather than its reduced expression. The results obtained using the chemiluminiscence method (CL) argue for increased oxidative stress and increased ROS production. The enzyme NAD(P)H-oxidase problably participates in ROS production in the later phases of diabetes. Oxidative stress was also connected with decreased levels of reduced glutathione (GSH) in the early phase of diabetes. After 10 weeks of diabetes, adaptational mechanisms probably took place because GSH levels were not changed compared to controls. Antioxidant properties of SMe1EC2 found in vitro were partly confirmed in vivo. Administration of SMe1EC2 protected endothelial function. It significantly decreased endothelaemia of diabetic rats and improved endothelium-dependent relaxation of arteries, slightly decreased ROS-production and increased bioavailability of ·NO in the aorta. Further studies with higher doses of SMe1EC2 may clarify the mechanism of its endothelium-protective effect in vivo.

Severe Hypoxia Inhibits Prostaglandin I2 Biosynthesis and Vasodilatory Responses Induced by Ionophore A23187 in the Isolated Rabbit Ear

The present study was designed to test the hypothesis that lack of oxygen in severely hypoxic tissue may inhibit arachidonic acid oxygenation and thereby result in an inhibition of eicosanoid synthesis. Hypoxia was induced in the isolated rabbit ear, and arachidonate metabolism and peripheral resistance of the preparation were monitored simultaneously. Severe hypoxia completely inhibited the biosynthesis of prostaglandin I2 induced by ionophore A23187 and converted the vasodilatory response observed under normoxia into vasoconstriction. The cyclooxygenase 1 inhibitor SC560 (1 µmol/l) effectively inhibited the normoxic prostaglandin I2 biosynthesis, while the cyclooxygenase 2 inhibitor DFU (1 µmol/l) did not. Neither SC560 nor DFU affected normoxic vasodilatory responses, indicating no involvement of prostanoids. The nitric oxide (synthase inhibitor Nω-nitro-L-arginine methyl ester (100 µmol/l) converted the vasodilation into vasoconstriction, similar to what was observed under hypoxia, suggesting that the hypoxia-mediated conversion might occur due to the inhibition of nitric oxide.

Hypoxia-induced inhibition of calcium channels in guinea-pig taenia caeci smooth muscle cells

1 The effects of hypoxia on whole‐cell current in single smooth muscle cells and on a high K+‐induced contraction of strips of the guinea‐pig taenia caeci were studied. 2 In physiological salt solution (PSS) and K+‐based pipette solution, hypoxia (PO2= 20 mmHg) reversibly inhibited both the inward Ca2+ current (ICa) and outward Ca2+‐activated K+ current (IK(Ca)) components of the whole‐cell current. 3 In PSS and Cs+‐based pipette solution, hypoxia reversibly suppressed ICa by 30 ± 5% at 0mV. 4 When Ba2+ was used as a charge carrier, the IBa was suppressed by hypoxia in a potential‐dependent manner, with the maximum of 40 ± 7% at +10mV. Alterations of concentrations of egta, GDBβS or ATP in the pipette solution did not change the inhibitory effects of hypoxia on ICa and IBa. 5 In PSS with 2 mm CaCl2 replaced by CoCl2, hypoxia did not affect the Ca2+ influx‐independent potassium current. 6 In cells voltage clamped at ‐20 mV hypoxia reversibly inhibited the spontaneous transient outward currents. 7 The response of high K+‐contracted taenia caeci to hypoxia was composed of an initial rapid relaxation followed by a small transient contraction and slow relaxation. The transient contraction was blocked by atropine (1–10 μm), while relaxations were unaffected by atropine and guanethidine (10 μm). 8 The results show that hypoxia reversibly inhibits ICa and secondarily suppresses IK(Ca) due to decreased Ca2+ influx through Ca2+ channels. 9 It is suggested that inhibition of ICa was responsible for the rapid relaxation, whereas transient contraction may have been due to release of acetylcholine from nerve terminals upon hypoxia.

ROLE OF EXTRA- AND INTRACELLULAR CALCIUM IN THE CONTRACTILE ACTION OF AGONISTS IN THE GUINEA-PIG ILEUM

SummaryThe effects of Ca2+-channel blockers (nifedipine and verapamil), EGTA, caffeine or the removal of external Ca2+ on the contractile action of different agonists and transmural electrical stimulation were examined in isolated segments of the proximal and terminal part of the guinea-pig ileum. The effects of agonists and nerve stimulation on membrane potential were also studied by means of the sucrose gap method. Acetylcholine-elicited contractions in both parts and noradrenaline-as well as histamine-induced contractions in the terminal part of the ileum were composed of an initial phasic and a sustained tonic component. Single pulse transmural nerve stimulation elicited smooth muscle twitches, whereas addition of CaCl2 to the tissue bath containing Ca2+-free and high-K+ medium elicited a sustained contraction. Both verapamil and nifedipine were more potent in inhibiting the tonic phase of the responses to the agonists or CaCl2 than inhibiting the phasic contractions elicited by transmural nerve stimulation, acetylcholine or noradrenaline. The excitatory junction potentials (e j.p.s.) as well as smooth muscle twitches were reduced only by high nifedipine concentrations. The effects of acetylcholine on membrane potential and input membrane resistance were affected minimally by the omission of extracellular Ca2+, while the contractions gradually disappeared on repetitive agonist application in the absence of external Ca2+ and were blocked by caffeine preexposure. In Ca2+-free solution noradrenaline and histamine partially reduced each others motor effect, while neither of them changed the contractile action of acetylcholine, yet the contraction induced by noradrenaline was prevented and that of histamine significantly reduced by preexposure to acetylcholine. These results suggest that the potency of acetylcholine to release Ca2+ from its caffeine-sensitive intracellular stores is much higher than that of histamine and noradrenaline.

Effect of illuminated nifedipine, a potent antioxidant, on intestinal and vascular smooth muscles

1 The effects of nifedipine (Nif) and its illuminated nitroso product nitrosopine (NTP) were investigated on lipid peroxidation, KC1 elevated smooth muscle tension, and ionic currents of single smooth muscle cells. 2 Illumination of Nif at 400–700 nm within 24–48 h changed it completely to a potent antioxidant, NTP. 3 Nif relaxed the KCl‐induced contractions of guinea‐pig taenia caeci and rat aorta and reduced the amplitude of the evoked inward Ca2+ current of taenia caeci cells in a concentration‐dependent manner. NTP (up to 100 μm) was ineffective in this respect. Pretreatment by NTP (10 μm) did not affect the actions of Nif. 4 The evidence suggests that NTP, generated by day‐light illumination from Nif, exerts antioxidant activity but is devoid of voltage‐dependent Ca2+ channel (VDC) blocking property and does not interfere with the action of Nif on the smooth muscle cell membrane VDC.

Pharmacological studies with beta-adrenoreceptor blocking agents I. Effect on the smooth muscle of the taenia coli of the guinea pig.

Abstract The action of new beta-blockers of VUFB series (VUFB 6502, VUFB 8102, VUFB 8227, and trimepranol) (Fig. 1) was analyzed in smooth msucle of guinea pig taenia coli by the double sucrose-gap method. All the studied beta-blockers increased the spontaneous spike activity without changes in membrane potential. The amino-analogues (VUFB 8101, VUFB 8102, VUFB 8227) as well as practolol were found to be 50 to 100 times less active than the oxy-derivatives (VUFB 6502 and Trimepranol) for the inhibition of spike activity, muscle relaxation and membrane hyperpolarization evoked by isoprenaline. None of the studied compounds had a pronounced alpha-blocking activity. The structure-activity relationship of the studied compounds was discussed.

Effects of reactive oxygen species and neutrophils on endothelium-dependent relaxation of rat thoracic aorta

Effects of reactive oxygen species and neutrophils on endothelium-dependent relaxation of rat thoracic aorta Reactive oxygen species (ROS) are produced in different metabolic processes including the respiratory burst of neutrophils accompanying local inflammation. The aim of this study was to analyze the effects of N-formyl-methionyl-leucyl-phenylalanine (FMLP)-activated neutrophils, isolated from the guinea pig peritoneal cavity, on isolated rings of a large (conduit) artery, the rat thoracic aorta. FMLP-activated neutrophils enhanced the basal tension increased by α1-adrenergic stimulation. In phenylephrine-precontracted aortae, they elicited marked contraction, while in noradrenaline-precontracted rat aortal rings they caused a biphasic response (contraction-relaxation). To eliminate interaction of activated neutrophils with catecholamines, in the subsequent experiments the basal tension was increased by KCl-induced depolarization. Activated neutrophils evoked a low-amplitude biphasic response (relaxationcontraction) on the KCl-induced contraction. Not only the acetylcholine- and A23187-induced relaxations but also the catalase sensitive hydrogen peroxide (H2O2) elicited contractions were endothelium-dependent. Even though the acetylcholine-induced relaxation was changed by activated neutrophils and by the ROS studied, their effects differed significantly, yet none of them did eliminate fully the endothelium-dependent acetylcholine relaxation. The effect of activated neutrophils resembled the effect of superoxide anion radical (O2•-) produced by xanthine/xanthine oxidase (X/XO) and differed from the inhibitory effects of Fe2SO4/H2O2-produced hydroxyl radical (•OH) and H2O2. Thus O2•- produced either by activated neutrophils or X/XO affected much less the endothelium-dependent acetylcholine-activated relaxation mechanisms than did •OH and H2O2. In the large (conduit) artery, the effects of activated neutrophils and various ROS (O2•-, •OH and H2O2) seem to be more dependent on muscle tension than on endothelial mechanisms.