Effects of GABA(B) 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.

Roentgenographic study of ethosuximide-induced functional changes in rat gastrointestinal tract and their modulation by Nivalin in a chronic experiment.

Ethosuximide, a typical antiabsence drug, causes gastrointestinal complaints in the drug-treated patients. In the present study we investigated in an experimental model the functional disturbances occurring in rat gastrointestinal tract (GIT) after a 100-day chronic administration of ethosuximide. Contrast radiographic study of rat gastrointestinal tract was used. The mechanical activity of GIT smooth muscle (SM) preparations was measured using an in vitro isometric technique. The 100-day ethosuximide treatment induced atonia, disturbed peristalsis, and lead to a delay of the contrast material evacuation from the gastrointestinal tract combined with a reduction of the acetylcholine effect on the contractions of GIT smooth muscles in ethosuximide-treated rats. Nivalin cannot eliminate the ethosuximide-induced disturbances in the gastrointestinal tract after a 100-day administration of ethosuximide to the rats. It is thus assumed that Nivalin is not capable of compensating the inhibiting effect of ethosuximide. The authors assume that desensitization of acetylcholine receptors may occur and this reduces the effect of Nivalin action.

Altered bioelectrical and mechanical activities of rat gastric smooth muscle preparations by inhibiting enterocytogenin.

Inhibiting enterocytogenin (IEG), a 4.5 kDa nucleopeptide isolated from pig intestinal mucosa induced dose-dependent alterations in the spontaneous contractile and bioelectric activities of rat gastric smooth muscle when applied at 10(-8) to 10(-4) M. Two separate phases were apparent in the effects observed, an initial contractile phase followed by a relaxation phase. The depolarization and the related contraction were reduced by amiloride and to a lesser extent by nifedipine. This reduction resulted in a corresponding decrease in the magnitude of the subsequent relaxation phase. Charybdotoxin and apamin caused a statistically significant decrease in the hyperpolarization and the magnitude of the relaxation phase and increased the duration of the contractile phase. On a caffeine or noradrenaline background the effects induced by IEG were diminished, suggesting that they are mediated through Ca2+ release from the intracellular Ca2+ stores. We hypothesize that the depolarization induced by IEG involves activation of the voltage-dependent Ca2+ channels with subsequent stimulation of the Ca(2+)-dependent K+ channels and late development of hyperpolarization.

Effect of butyric short-chain fatty acids on the bioelectric and contractile activity of gastrointestinal smooth muscle tissues.

The present study was undertaken to investigate the effect of butyric (C4) short-chain fatty acids on the bioelectric and contractile activity of smooth muscle (SM) tissues from rat and guinea-pig gastrointestinal tracts. The study was conducted in vitro on isolated SM preparations of rat gastric corpus and guinea pig taenia coli. The following methods were used: 1. Recording of bioelectric activity using the single sucrose gap method. 2. Isometric recording of smooth muscle contractility. The results showed that there was potentiation of the spontaneous bioelectric and contractile activities of SM preparations in the presence of butyrate (a salt of the butyrate short-chain fatty acid). This effect was accompanied by an increase of Ca(2+)-influx in the SM cells. The immediate cause for this process was elevation of prostaglandin F2-alpha level in the SM tissues. The present study suggested the following conclusions: 1. Butyric short-chain fatty acid increases the contractility of gastrointestinal SM preparations of experimental animals. 2. This effect is produced by the immediate action of PGF2-alpha on smooth muscles where they are found to have elevated levels in the presence of butyrate.

Effects of ethosuximide on the cerebral vasculature and hemodynamics of rats.

The development of epileptogenic activity has been proven to be closely related to changes in cerebral blood flow. This study was designed to examine the effects of ethosuximide, a widely used anticonvulsant drug, on cerebral hemodynamics. White Wistar rats were treated (p.o.) with 100 mg/kg b.w. ethosuximide. Three hours after administration, changes in cerebral blood flow due to vasodilation were recorded by means of angiography. Using the single sucrose gap method it was found that ethosuximide caused hyperpolarization of smooth muscle sample from rat internal carotid artery by 5.4 +/- 1.6 mV. The hyperpolarization was related to relaxation of smooth muscle tissue of vessels, which was recorded isometrically. Ethosuximide significantly depressed vascular reactions to the vasoconstrictive agents noradrenaline and serotonin. Ethosuximide-induced reaction was not significantly influenced by the Ca2+ antagonist verapamil, but was reduced by caffeine (10(-4) M) and apamine (5.10(-6) M), the latter being a blocker of Ca2+ -dependent K+ channels. The experimental data strongly suggest that changes in bioelectric and contractile activity of arterial smooth muscle samples are a result of Ca2+ -dependent K+ efflux, provoked by calcium which has been derived from intracellular Ca2+ store. These results show that ethosuximide-induced changes in cerebral blood flow are caused by reduced reactivity of smooth muscle tissue and vascular dilatation.

Disturbances in rat smooth-muscle induced by a substance with fungicide action.

The fungicide substance QAS [N,N,N',N'-tetramethyl-N,N'-di(8,15-dichloropentadeca-5,10- dien)ethylenediamine methylsulphate] has a biphasic effect on the spontaneous electrical and mechanical activity of smooth-muscle samples of rat corpus and guinea-pig taenia coli. During the first phase of QAS application membrane depolarization and increased spontaneous spike frequency were recorded. The tone of the preparations (resting tone) increased transiently. Calcium ion-entry blockers did not affect the contractile effect of QAS, but K(+)-channel blockers and some modulators of the second messenger system abolished or decreased it. During the second phase depolarization increased progressively, spike frequency decreased and the increase in resting tone recorded during the first phase was eliminated. The results reveal that the long-lasting depolarizing effect of QAS (in concentrations used for plant protection) probably inactivates the entry of Ca2+ into the smooth-muscle cells and disturbs Ca2+ homeostasis.

The ethosuximide-induced hyperpolarization of smooth muscle tissues--a cause of functional changes in the gastrointestinal tract of rats--is provoked by CA(2+)-dependent K(+)-efflux.

Ethosuximide is an antiepileptic drug successfully used in the treatment of petit mal especially in childhood. Clinical investigations reveal that ethosuximide has a number of adverse side effects on the gastrointestinal tract (GIT) of patients which may include heaviness, anorexia, pains in the region of the stomach, accompanied sometimes with nausea and vomiting. In the present study we attempt to explain the mechanisms of some of the drug's adverse side effects using an experimental animal model. White rats were employed in the experiments during which they were treated daily with ethosuximide (100 mg/kg) for 100 days. We made use of the following methods in the study: 1. Contrast X-rays study of the gastrointestinal tract. 2. Recording of the bioelectric activity of isolated smooth muscle strips using the sucrose-gap method. 3. Recording of the contractile activity of isolated smooth muscle. Characteristic changes occurring after treatment of rats with ethosuximide include atony of the stomach and the intestines, hypertonus in separate duodenal segments, diminished peristaltic activity, and delayed passage at the 24th hour. The drug inhibits the spontaneous contractile activity of isolated smooth muscle strips from rat gastrointestinal tract. In some duodenal preparations is minimised in the presence of apamin, an inhibitor of Ca2+(-dependent) K+ channels (Ka+(Ca)), while in duodenal preparations this effect may undergo a reversion. In the presence of coffeine the action of ethosuximide on the smooth musculature of rat gastrointestinal tract is reduced significantly. We hypothesis that the observed functional changes in the gastrointestinal tract occur as a result of the hyperpolarizing effect of ethosuximide on the gastrointestinal musculature caused by the outcoming K+(CA)-efflux.

Effect of sodium valproate on the spontaneous contractile and bioelectric activity of smooth muscle fibres isolated from experimental animals.

Experiments were carried out with smooth muscles preparations of 24 rats (gastric corpus) and 36 guinea pigs (gastric corpus and taenia coli). Their contractile responses were recorded isometrically using tensile transducers. The bioelectric activity was determined by the single sucrose-gap method. Depending on the concentration sodium valproate elicits two types of responses from the smooth muscle of gastrointestinal tract of rats and guinea pigs: a contractile response, at concentrations less than 10(-4) g/ml, and a relaxant response, at concentrations higher than 10(-4) g/ml. At concentrations below 10(-4) g/ml sodium valproate induces contractions of the smooth muscle taken from the rat and guinea pig gastrointestinal tract. These contractions can be abolished by indomethacin. It may be concluded, therefore, that the contractile effect of sodium valproate has a prostaglandin basis. At concentrations higher than 10(-4) g/ml, sodium valproate hyperpolarizes the smooth muscle tissues, reduces the frequency and amplitude of the spontaneously generated spike potentials and relaxes the preparations. These effects are blocked by picrotoxin. Sodium valproate in high concentrations increases the endogenous level of the gamma-aminobutyric acid stimulating at the same time the prostaglandin synthesis which is inadequate to compensate the relaxant effect induced by elevated level of the endogenous gamma-aminobutyric acid.

Effect of the butyric short-chain fatty acid on the intracranial pressure and EEG of rabbits.

In the present study we followed the changes in the intracranial pressure and EEG activity of rabbits caused by the butyric short-chain fatty acid infused as an 0.2 M solution at the rate of 12 ml/h. Changes in the rabbit's normal EEG of paroxysmal nature were initially observed, followed by a rise of intracranial pressure as a result of the edema that developed in the brain. Pretreatment of the animals with an inhibitor of the prostaglandin (PG) synthesis (indomethacin, i.v. 10 mg/kg b.w.) prevented the appearance of paroxysms. The intracranial pressure increased in the presence of indomethacin, but there was a tendency towards reduction of the maximal value reached in the control animals. We conclude that the PG system participates to a varying degree in the genesis of the butyrate-induced changes in the bioelectric cerebral activity and intracranial pressure.

Effects of the medium chain octanoic fatty acid on the contractile activity of vascular smooth muscle tissues.

Multiple elevation of the octanoic fatty acid level in human sera is often observed in some hepatic diseases which are accompanied by cardiovascular disorders, hypotension, and increased cardiac stroke volume. Different experiments reveal the hypotensive effect of octanoate. The present study investigates the octanoate action on the bioelectric and contractile activity of vascular smooth muscle tissues. Octanoate is shown to cause hyperpolarization of smooth muscle cells, reduction of spike potential frequency, and relaxation of vascular muscles. These effects are inhibited by indomethacin, which proves their prostaglandin nature. Octanoate action on stomach smooth muscle strips is inhibited by SC 19220, a specific competitive inhibitor of the contractile action of prostaglandins E2 and F2 alpha on the same tissues in vitro. Using thin-layer chromatography two PG fractions were isolated from arterial blood of octanoate treated rats and from a control group of rats. These fractions have identical chromatographic characteristics with those of PGE2 and PGF2 alpha. The level of the PG fraction with Rf value similar to that of PGE2 is significantly increased in octanoate treated animals while the other fraction tends to decrease.

Effects of the butyric short-chain fatty acid on the bioelectric brain activity of rabbits.

The effects of the butyric short-chain fatty acid, an agent with proved comagenic action, on the bioelectric brain activity of rabbits was studied. In all monopolar leads, paroxysms were recorded which manifested themselves 15 to 30 minutes after the infusion of butyrate. The analysis used F2 exogenic prostaglandins and indomethacin, an inhibitor of prostaglandin synthesis. It was found that the system for prostaglandin synthesis plays a role in the effects of butyrate.

Influence of short-chain fatty acids on vascular tone.

Results from research on the influence of short-chain fatty acids (SCFA) (C3-C6) on vascular tone are reported. Isolated vascular smooth muscle strips were studied in vitro and the arterial blood pressure of guinea-pigs injected with SCFA was taken. On the basis of results from these first two methods, the level of PG F2 alpha was determined by radioimmunoassay. The experiments indicate that in vitro the SCFA have spasmogenic effects which are blocked by indomethacin and aspirin and which are reduced by the inhibitor of the activating effect of PG F2 alpha, PG E2, and PG I2-SC19220. The effects of SCFA on smooth muscle strips used as a bioassay are analogous to the effects of PG F2 alpha on the same tissue. The injection of butyric acid into guinea-pigs causes hypertension which is not manifest if indomethacin pretreatment is carried out. Radioimmunoassay results indicate that the level of PG F2 alpha in the blood of animals treated with butyric acid is significantly increased.

The effect of octanoic fatty acid on the cardiovascular system of the guinea pig.

The aim of the study was to clarify the role of octanoic acid (OA) in the development of cardiovascular disorders occurring in some liver diseases associated with high OA levels in blood serum. The effect of OA (caprylic acid) on the functional state of the cardiovascular system was studied in guinea pig by means of the thermodilution method and ultrasound Doppler echography. It was found that, as a result of its inotropic action, OA decreases arterial pressure and vascular resistance while increasing cardiac output. The effect of OA can be inhibited by the administration of indomethacin, a fact suggesting the prostaglandin system plays a role in the mechanism of cardiovascular action of OA. This hypothesis represents a new concept regarding the pathogenesis of the hyperdynamic cardiovascular syndrome in liver cirrhosis and hepatic encephalopathy.

The impact of butyric acid on the cardiovascular system.

The influence of sodium salt of butyric acid (C4H7NaO2) on the functional state of the cardiovascular system was studied on 12 guinea-pigs and 15 rabbits by the thermodilution method. The following parameters were determined: cardiac output (CO), arterial blood pressure (AP), total peripheral vascular resistance (TPVR), and in rabbits the heart rate (HR). It was found that butyric acid induces significant changes in TPVR, which correlate with changes in CO and AP. These changes could to a considerable extent be prevented by the administration of indomethacin. Haemodynamic changes induced by butyric acid are primarily connected with changes in vascular tonus, induced by the action of F2 alpha prostaglandins whose synthesis is intensified by the influence of butyric acid.