Valentin I. Turiiski

Calcium-independent tacrine-induced relaxation of rat gastric corpus smooth muscles

Tacrine, a non-competitive reversible acetylcholinesterase and butyrylcholineserase inhibitor, caused a concentration-dependent tonic contraction of gastric smooth muscle preparations in the concentration range 1 x 10(-7) mol/L - 1 x 10(-5) mol/L, whereas concentrations higher than 2 x 10(-5) mol/L induced a biphasic effect; a short-time contraction was followed by a prolonged relaxation. To shed some light on the mechanism underlying this untypical relaxation, the amplitude of mechanical reactions caused by tacrine were compared with those of tacrine in the presence of atropine, ipratropium, metrifonate, TTX, nifedipine, D-600, caffeine, apamin, and charybdotoxin. The results obtained revealed that the relaxation was neither cholinergic in nature, nor mediated by the influence of the drug on intramural neuronal structures. It was not influenced by processes inducing changes in cytosolic Ca2+ levels. This assumption was confirmed by experiments with permeabilized muscle preparations that were pre-contracted in a solution with pCa 5.5. Tacrine relaxed the smooth muscles in spite of the constant intracellular Ca2+ concentration resulting from the permeabilization. These findings argue that tacrine at concentrations higher than 2 x 10(-5) mol/L has a desensitizing effect on the contractile apparatus of gastric corpus smooth muscle preparations towards Ca2+.

Comparative X-Ray study of galantamine and tacrine on the evacuatory function of rat gastrointestinal tract

A The acetylcholinesterase inhibitors galantamine and tacrine are used to treat Alzheimer’s disease. However, these compounds also affect the gastrointestinal (GI) tract. Here, we compared and analyzed both the effects of galantamine-and tacrine on the evacuatory kinetics of the GI tract in rats. Rats were untreated (n=15) or treated with galantamine (one daily dose of 1 mg/kg per os for 21 days; n=17) or tacrine (one daily dose of 0.5 mg/kg per os for 21 days; n=13) and evacuatory kinetics were assessed using radiological methods. Galantamine initially slowed and then accelerated evacuation, which is characteristic of the majority of cholinesterase inhibitors and is a result of the endogenous acetylcholine accumulated in the GI tissues. In the tacrine-treated rats the contrast medium was kept in the stomach and cecum and its evacuation time was reliably increased. These results indicate that when administered for 20 days, galantamine and tacrine have different effects on motor and evacuatory function in the GI tract of rats, because at certain levels of the tract the tacrine-action is dominated by specific non-cholinergic and non-anticholinesterase mechanisms.

Comparing hyoscine and drotaverine effects on colon in CT colonography

Hyoscine and drotaverine effectiveness was compared for the purposes of achieving optimum distension following insufflation in CT colonography. The in vitro effects of hyoscine and drotaverine on tone and contractility of SM preparations isolated from different areas of human colon were studied by isometric registration of contractile activity. Both medications have a relaxing effect on SM preparations and inhibit their spontaneous contractions. The drotaverine-induced effects were reliably more marked than the hyoscine-induced ones. CT colonography was performed in 70 patients who were injected with equal doses of either hyoscine (n=32) or drotaverine (n=38). The degree of drug-induced distension in both groups was determined by measuring the lumen of the colon on a 2D reconstruction. In most colon areas the width of the distended lumen was greater in the drotaverine-treated patients. We concluded that drotaverine can be used as a means to facilitate colonic distension.

Participation of cAMP in tacrine-induced gastric smooth muscle relaxation

Tacrine, a well-known acetylcholinesterase inhibitor, applied in concentrations higher than 2×10−5 mol/l promoted Ca2+-independent relaxation of rat gastric smooth muscles in experiments in vitro. The relaxation was not cholinergic and was a result of influence of tacrine over intracellular signaling pathways regulating smooth muscle contraction/relaxation. The nature of this untypical muscle relaxation was studied by using smooth muscle strips isolated from rat stomach. Their bioelectrical and mechanical responses were recorded after treatment with tacrine and different activators or blockers of intracellular pathways involved in muscle contractility. Following the activation of adenylate cyclase with 1×10−6 mol/l forskolin and increase in the concentration of cyclic adenosine monophosphate (cAMP) after application of 4×10−5 mol/l SQ22536, a significant decrease in the muscle relaxation was observed. Theophylline (2×10−4 mol/l), a phosphodiesterase inhibitor, had no effect on the amplitude of tacrine-induced relaxation. The latter was also reduced by inhibition of protein kinase A (PKA) with 5×10−6 mol/l KT5720. These findings support the assumption that tacrine promoted smooth muscle relaxation through PKA-induced phosphorylation and inhibition of myosin light chain kinase activity. The reduction of spike-linked Ca2+ influx provoked by tacrine was probably a secondary contributing process, associated with an influence of increased cAMP level on Ca2+ channels.

Effects of GABAB receptor antagonists on spontaneous and on GABA-induced mechanical activity of guinea-pig smooth muscle preparations

The majority of GABA(B) receptor antagonists have been based on alterations of the acidic moiety of gamma-aminobutyric acid (GABA) or baclofen, such as the first selective antagonist phaclofen. More recently, a new structural class of compounds derived by p-alkyl substitution in the phosphinic analog of GABA, such as CGP35348 (3-amino-propyl-(diethoxymethyl)-phosphinic acid), have been introduced as GABA(B) receptor antagonists. The present study examine the influence of a series of structurally related phosphinic acid analogues on mechanical activity and their effect on GABA-induced reactions in ileal smooth muscle. In our experiments, GABA exerted a biphasic contractile-relaxation effect with pronounced dose-dependent characteristics. 3-[[1-(S)-(3,4-Dihydrophenyl) ethyl]amino]-2-(S)-hydroxy-propyl]-(phenylmethyl)-phosphinic acid hydrochloride (CGP55845A) induced prolonged relaxation without changing the phasic activity of the ileum preparations. [3-[1-R-[[2-(S)-hydroxy-3-[hydroxy-4-methoxyphenyl]-methyl]-phosphinyl]-propyl]-aminoethyl]-benzoic acid (CGP62349) did not change the mechanical activity of smooth muscle preparation. Trans 3-[6-[[Cyclo hexylmethyl-hydroxy-phosphinyl]-methyl]-3-morpholinyl]-benzoic acid (CGP71982) itself induced smooth muscle contractions. GABA(B) receptor antagonists decreased concentration-dependently the relaxation phase of the action of GABA from 50% to 90%. Their effect on the contractile phase of the action of GABA was quite different-CGP55845A decreased it dose-dependently, whereas CGP62349 and CGP71982 did not change it significantly. These findings prompted us to assume that the GABA(B) receptor antagonists studied, being phosphinic analogues, probably act on GABA(B) receptors in guinea-pig ileum smooth muscles.

Biochemical Changes in Experimental Rat Model of Abdominal Compartment Syndrome

Abstract Background: Increased intra-abdominal pressure (IAP) causes tissue ischemia, subsequent hypoxia, and impairment of normal tissue metabolism. Elevation of IAP above 20 mmHg leads to progression of abdominal compartment syndrome (ACS) that is associated with organ dysfunction or failure not previously manifested. Aim: To evaluate the eff ects of diff erent grades and time of exposure to IAP on biochemical parameters and oxidative stress in organs aff ected by ischemia using previously developed rat model. Results: Three experimental groups exposed to diff erent IAP and time frames were tested for liver, kidney, and pancreas injury by measuring the activities of tissue specifi c enzymes in blood serum. Elevated activities of aspartate aminotransferase, pancreatic amylase, lipase, and higher concentrations of D-lactate, urea, and creatinine were found in some of the experimental groups compared to a control group of animals not subjected to increased IAP. Increased levels of biomarkers of oxidative stress as well as decrease in concentration of the major cellular antioxidant glutathione indicated the presence of oxidative injury as a result of elevated IAP. Conclusions: The developed rat model is appropriate to study the mechanism and manifestation of tissue injury during diff erent grades of elevated IAP but also to test approaches aimed to attenuate the detrimental eff ects of ACS. This study also underlines the necessity of using not a single but a set of biochemical parameters in order to assess the severity of tissue injury during elevated IAP and progression to ACS.

Effects of the Novel High-affinity 5-HT(1B/1D)-receptor Ligand Frovatriptan on the Rat Carotid Artery

Abstract Background: In blood vessels 5-HT stimulates sympathetic nerves, the endothelium and vascular smooth muscle cells. Triptans are specific anti-migraine drugs and they activate the serotoninergic 5HT1b/d receptors causing vasoconstriction of the cerebral vessels. Aim: To evaluate the effect of frovatriptan on isolated rat carotid artery. Methods: Contractile activity of the preparations was registered isometrically. Krebs solution (pH = 7.4) was used for washing smooth muscle (SM) preparations aerated with 95% O2 and 5% CO2 at 37°C. The 60-minute adaptation of tone level of preparations was taken as a starting tone and the changes such as contraction or relaxation were calculated using it. Results: Frovatriptan (1×10-6 mol/l - 1×10-5 mol/l) induced a contraction, but at higher concentrations it caused relaxation of the carotid artery. The L-norepinephrine contractile reaction was enhanced in the presence of frovatriptan. In the presence of 5-HT2 receptor antagonist, methysergide, frovatriptan increased the relaxation. In the presence of the specific α-1 receptor antagonist, prazosin, the frovatriptan-induced relaxation decreased. Conclusion: The observed contractile effect of frovatriptan is probably associated with the main effect of the drug - activation of the serotoninergic 5HT1B /1D receptors causing vasoconstriction of the cerebral vessels and their anti-migraine effect. At higher concentrations, frovatriptan, most likely via some non-specific mechanism, could activate the following intracellular chain reaction: stimulation of α1D could activate eNOS which may increase in the concentration of NO which results in the final effect of relaxation.

Tacrine-induced tachyphylaxis in gastric smooth muscles

Tacrine is a medication applied in cases of mild to moderate dementia in Alzheimer’s disease. By blocking acetylcholinesterase activity the drug increases the concentration of acetylcholine, whose effects influence the functions of different organs and systems of the body. The effect of tacrine on smooth muscle preparations isolated from rat stomach was studied by isometric registration of muscle contractility. Our investigations found a specific significant systematic decrease in the strength of consecutive tacrine-induced contractions of smooth muscle preparations, a phenomenon known as tachyphylaxis. The tacrineinduced tachyphylaxis was significantly inhibited by SQ22536 (inhibitor of adenylate cyclase activity), by blockers of nitric oxide synthase and KT5823 (inhibitor of protein kinase G). The process was not influenced by cyclopiazonic acid (specific blocker of sarco/endoplasmic reticulum Ca2+-ATPase,) and atropine (blocker of M-cholinergic receptors). We hypothesize that the overlapping and different time-development of the two opposing processes: smooth muscle contraction caused by acetylcholinesterase inhibition and tacrine-induced relaxation influenced by synthesis of nitric oxide, results in tachyphylaxis.

Sensitizing Effect of Tacrine on M-Cholinergic Receptors in Gastric Smooth Muscle of Rats

Sensitizing Effect of Tacrine on M-Cholinergic Receptors in Gastric Smooth Muscle of Rats Aim: To find if tacrine exerts a sensitizing effect on the cholinergic receptors of gastric smooth muscles, and study some of the mechanisms inducing it and measure the relative intensity of tacrines effects on contractile activity. Material and methods: Isometric recording of the mechanical activity of gastric smooth muscle preparations; determination of acetyl-cholinesterase activity in smooth-muscle tissue homogenates using Ellmans method. Results: We found that the threshold concentration for tacrine not reducing the acetylcholinesterase activity and not having an effect on the smooth muscle preparations was 1×10-8 mol/l. This concentration, however, significantly increased the acetylcholine-induced contraction compared with the controls, after the smooth-muscle tissue was incubated for 60 or 100 min. Treating smooth-muscle preparations with tacrine in a concentration of 5×10-6 mol/l triggered a contraction induced by the drugs anti-cholinesterase activity. A secondary contraction was induced after 38.6 ± 5.6 min. There was no secondary contraction after the control acetylcholine-induced effect. Atropine (1×10-6 mol/l) inhibits this effect. Preliminary treatment of smooth muscle preparations with hexamethonium (1×10-6 mol/l) did not change significantly the intensity of the first phase of tacrine-induced contraction and shifted in time the appearance of the second contractile phase. Conclusion: Tacrine has a sensitizing effect on M-cholinergic receptors; it occurs after a long incubation of the gastric smooth muscles with the drug and is manifested as a secondary contraction which is shifted in time and is significantly inhibited by atropine. Проявления сенсибилизирующе-го действия tacrine на м-типа холинергические рецепторы в гладкой желудочной мускулатуре крысы Цель: Изучить наличие сенсибилизирующего действия tacrine на холинергические рецепторы в желудочных гладких мышцах, изучить также и некоторые механизмы, вызывающие это действие, как и отно-сительную силу его эффекта на сократительную активность. Методы: Изометрическое регистрирование меха-нической активности желудочных гладкомышечных препаратов; определение ацетилхолинестеразной активности в гомогенатах гладкомышечной ткани по методу ЕПтап. Результаты: Как пороговая концентрация tacrine, не редуцирующая ацетилхолинестеразной активности и не оказывающая влияния на сократительную ак-тивность гладкомышечных препаратов определена концентрация 1×1 (У8 то 1/1. Она, однако, достоверно повышает ацетилхолин-индуцированную контрак-цию по отношению к контрольной через 60 или 100 min. инкубации гладкомышечной ткани. Воздействие на гладкомышечные препараты посредством 5×1 0~6 mol/l tacrine провоцирует контракцию, выз-ванную антихолинестеразным действием лекар-ства. Через 38.6 - 5.6 min развивается второй контрактилъный процесс. При контрольном аце-тилхолин-индуцированном эффекте подобный второй контр актилъный процесс отсутствует. В присутствии atropine (lxl 0~6 mol/l) эффект не проявляется. Предварительное воздействие на гладкомышечные препараты lxl 0~6 mol/l hexametho- титом не изменяет достоверно силу первой фазы tacrine индуцированной контракции и отодвигает во времени появление второй контрактилъной фазы. Заключение: Tacrine обладает сенсибилизирующим эффектом на М-типа холинергические рецепторы, проявляющимся после продолжительной инкубации с помощью лекарства и проявляется в виде второй, отодвинутой во времени, контракции, которая достоверно ингибируется атропином (atropine).

Effect of elevated intra-abdominal pressure on the contractile activity and reactivity of smooth muscle tissue from rat gastrointestinal tract to galantamine and drotaverine (No-Spa).

Effect of Elevated Intra-Abdominal Pressure on the Contractile Activity and Reactivity of Smooth Muscle Tissue from Rat Gastrointestinal Tract to Galantamine and Drotaverine (No-SPA) Aim: The aim of the present study was to determine the nature and intensity of changes in the contractile activity and reactivity of gastrointestinal smooth muscle tissue in conditions of increased intra-abdominal pressure. Methods: A method for recording isometric contractions of isolated smooth muscle preparations from gastric corpus, duodenum and sigmoid colon of rats was used. Results: Two groups of rats were used in the study - control animals and animals with elevated abdominal pressure. It was established that pressure of 25 mmHg for 60 min did not cause statistically significant change in the tone and parameters of the spontaneous contractions in all preparation types, as well as in their reactivity to drotaverine (no-spa). Statistically significant increase in the strength of the tonic effects of galantamine (1.10-6 - 1.10-3 mg/ml) was found in all types of smooth muscles preparations isolated from rats with increased abdominal pressure compared with preparations from the control rats. Conclusions: The statistically significant increase in the galantamine-induced effects on smooth muscle preparations is associated with increase in the contractile effectiveness of acetylcholine. M-type cholinergic receptors are predominantly involved in the processes, probably sensibilized from processes activated by the increased intra-abdominal pressure. Влияние повышенного интра-абдоминального давления на сократительную активность и реактивность гладкой мускулату ры гастроинтестинального трак та крысы к Galantamine Drotaverine (No-Spa) Цель: Установить характер и силу изменений, вызванных повышением интраабдоминалъного дав ления на сократительную активность гастро-интестиналъной мускулатуры. Методы: Использован метод регистрации изо метрических сокращений изолированных гладко-мышечных препаратов, взятых от gastric corpus, duodenum и sigmoid colon крысы. Результаты: Обследовано две группы крыс (кон трольная и с повышенным интраабдоминальным давлением). Установлено, что давление 25 mm Hg в течение 60 min значимо не изменяет тонус и параметры спонтанных сокращений всех видов препаратов, как и их реактивность по отношению к drotaverine (no-spa). Наблюдается достоверное нарастание силы тонических эффектов galan-tamine (1.10~6 - 1.10~3 mg/ml) при различных типах гладкомышечных препаратов, изолированных от крыс с повышенным интраабдоминальным давлением, по отношению к силе контрольных препаратов. Заключение: Достоверно увеличенная сила galantamine-индуцированных эффектов на гладкомышечныепрепараты связана с нарастанием контрактилъной эффективностиacetylcholine. В процессы включены в основном М-типа холинергические рецепторы, по всей вероятности сенсибилизированные про цессами, спровоцированными повышенным интра абдоминальным давлением.