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Biomedical subjects

V Bauer

Publications and source records attributed to V Bauer.

At least 55 records · Page 3Linked to original sources
PubMed1988

Action of histamine on nerve mediated responses of the guinea-pig ileum.

The effect of histamine on the responses of the guinea-pig ileum to stimulation of intramural nerves and to some potential nonadrenergic, noncholinergic (NANC) neurotransmitters was analysed. During sustained tonic histamine contraction, electrical stimulation of all intramural nerves elicited a biphasic response (contraction followed by after-relaxation) and application of ATP and bradykinin caused relaxation of the ileum in contrast to their contractile effect on basal tension. Histamine reduced contractile and augmented relaxatory NANC responses, and prevented capsaicin from producing any contractile effect and from significantly influencing the NANC contractions. The present results suggest that, besides its direct effect, histamine activates intramural nerve fibres, mainly the sensory ones, and unmasks NANC relaxation thus modifying the mechanical activity.

Animals↗
PubMed1988

Action of pentacaine on gastric acid secretion.

The action of pentacaine, a new prospective antiulcer drug with gastric cytoprotective activity, on gastric acid secretion was analysed and compared with the action of other antisecretory drugs. The drugs were given orally or intraduodenally to Wistar rats after pylorus ligation. The gastric acid secretion was studied under basal or stimulated (histamine, pentagastrin, carbachol) conditions. Oral administration of pentacaine, oxethazaine and procaine, in contrast to atropine, had no influence either under basal or stimulated conditions. However, intraduodenal administration of pentacaine significantly suppressed both the basal and stimulated gastric secretion. The present study suggests that the mechanism of antisecretory activity of pentacaine differs from that of anticholinergic and antihistaminergic drugs.

Animals↗
PubMed1988

Calcium and the activation of the alpha 1-adrenoceptors in the guinea-pig taenia caeci.

1. The actions of phenylephrine (0.1-100 mumol l-1) and methoxamine (0.1-100 mumol l-1) were compared with that of adrenaline (0.01-10 mumol l-1) using the single sucrose gap method and mechanical recording in the guinea-pig taenia caeci. Drugs were applied for variable periods of time. 2. The characteristics of the inhibitory effects of alpha-adrenoceptor agonists were the same when exposure time did not exceed 5 min. When the exposure was prolonged, in contrast to the sustained effects of adrenaline (0.1-3 mumol l-1), phenylephrine and methoxamine (1-10 mumol l-1) produced a transient inhibitory action. 3. During the delayed recovery phase of phenylephrine, adrenaline preserved its ability to suppress the spontaneous electrical and mechanical activities of the taenia both when phenylephrine was replaced by adrenaline or when adrenaline was applied in addition to phenylephrine. All the above effects were found in untreated preparations, as well as during blockade of muscarinic cholinoceptors by atropine (1.4 mumol l-1), beta-adrenoceptors by propranolol (3 mumol l-1) and release of endogenous catecholamines by guanethidine (2.5 mumol l-1). 4. In the presence of phorbol 12,13-dibutyrate adrenaline ceased to be effective, while the inhibitory action of phenylephrine was converted to a contraction. 5. In calcium-free conditions in the presence of EGTA (0.4 mmol l-1) the initial hyperpolarization induced by adrenaline and phenylephrine was significantly reduced and with repeated applications of the agonists the inhibitory response disappeared. Similar results were obtained using tissues treated with nifedipine (1 and 10 mumol l-1). When caffeine (30mmolI 1) was present in the calciumfree solution the alpha-agonists studied were unable to produce any membrane potential changes. 6. The present results imply that the inhibitory effect of alpha-adrenoceptor agonists is mediated by the opening of potassium channels, which are activated by calcium derived from an intercellular source supplied from the extracellular space via a nifedipine-sensitive mechanism.

Animals↗
PubMed1988

Effect of calcium entry blockade on the actions of phenylephrine on the taenia of the guinea pig caecum.

The interaction between phenylephrine and calcium entry blockers was studied on the taenia of the guinea-pig caecum using the double sucrose gap method. Sustained hyperpolarization, relaxation and attenuation of evoked electrical and mechanical activity were induced by non-cumulative addition of phenylephrine (0.1 to 250 mumol.1-1) for 2 to 4 min. When the alpha 1-adrenoceptor agonist was applied for a prolonged period (20 to 60 min) the initial inhibitory response gradually disappeared both at room temperature and at 32 degrees C. The renewed action potentials were accompanied by a positive afterpotential. The initial hyperpolarization and its delayed recovery in course of the phenylephrine effect were significantly reduced in calcium-free medium containing EDTA (2 mmol.1-1), after pretreatment with nifedipine (0.1 to 1 mumol.1-1), verapamil (10 to 100 mumol.1-1) or procaine (0.5 to 2 mmol.1-1). In contrast sodium nitroprusside (10 to 100 mumol.1-1) which produced biphasic changes similar to those of phenylephrine, did not affect the initial and delayed phase of phenylephrine action. Ba2+(5 mmol.1-1) could substitute for Ca2+ in the generation of action potentials but could not substitute for Ca2+ in the mechanisms responsible for the initial and delayed recovery phase of phenylephrine effects. In the presence of La3+ and Mn2+ (0.5 to 3 mmol.1-1) the phenylephrine effects were reduced. In contrast, in the presence of extracellular Ca2+, pretreatment with Mg2+ (12 mmol.1-1) or Ba2+ (5 mmol.1-1) did not affect the action of phenylephrine. It is concluded that activation of alpha 1-adrenoceptors results in the release of Ca2+ from an intracellular store, which leads to the opening od TEA-sensitive potassium channels, causing the initial phase of alpha 1-adrenoceptor action. Ca2+ is loaded into this intracellular store by entering the cell through the potential sensitive calcium channels. Although the mechanisms responsible for the delayed phase could not be clarified, its dependence on the presence of the initial phase is apparent.

Action Potentials↗
PubMed1987

The effects of methylxanthines, ethymizol, ephedrine and papaverine on guinea pig and dog trachea.

The study was aimed to compare the effects of pentoxyphylline, aminophylline, choline theophyllinate and ethymizol on guinea pig and dog trachea with those of theophylline, papaverine and ephedrine. The effects of these drugs on the basal tension, on dose-response curves for muscle contraction produced by histamine and on cAMP level were investigated in guinea pig trachea, together with their influence on the resting and histamine-evoked mechanical and membrane activities of dog trachea. Like papaverine, pentoxyphylline did not alter the resting membrane potential, although it relaxed both tracheal preparations, and it antagonised the effects histamine and raised the cAMP level of the smooth muscle. The effects of ethymizol were similar to those of theophylline and its water soluble derivatives (aminophylline and choline theophyllinate). Whereas, ephedrine although it decreased the basal tension and inhibited histamine-evoked responses, also elicited substantial hyperpolarization of the smooth muscle membrane with no effect on the cAMP level. These findings are consistent with the hypothesis that cAMP has an important role in the action of some bronchodilator drugs; however, it is concluded that the possibility of contributing of their action on membrane potential to their action needs to be considered. The similarity of the potencies of ethymizol and pentoxyphylline to that of classical bronchodilators in inhibiting contraction of guinea pig and dog tracheal smooth muscle suggests that they may have a therapeutic value.

Animals↗
PubMed1987

The action of adrenoceptor agonists and antagonists on the guinea pig and dog trachea.

The action of beta- and alpha-adrenoceptor agonists (isoprenaline, orciprenaline, noradrenaline, phenylephrine and ephedrine) and antagonists (propranolol, metipranolol, exaprolol, BL 445 and phentolamine) on the resting tension and cAMP level of the guinea pig and the mechanical and electrical activities of the dog trachea were studied. By activating beta 2-adrenoceptors, isoprenaline and orciprenaline relaxed the smooth muscle, elevated the membrane potential and attenuated the excitatory effect of histamine on membrane potential and muscle tension. Noradrenaline and phenylephrine, acting on alpha 1-receptors, did not affect the membrane potential and increased the basal tension of the dog trachea only insignificantly. Ephedrine, in high concentrations, however, hyperpolarized the smooth muscle membrane and relaxed the dog trachea, while it did not alter the cAMP level in the guinea pig preparations. It is, therefore unlikely that alpha 1-adrenoceptors play a major role in the excitation of the dog trachea under resting conditions whereas the participation of alpha 2-receptors in the mechanisms of adrenergic relaxation could not be ruled out. All the beta-adrenoceptor antagonists studied enhanced the action of low isoprenaline concentrations and competitively antagonized it in high concentrations. The order of their antagonistic potency in the guinea pig trachea was as follows: metipranolol greater than propranolol = exaprolol greater than or equal to BL 445. It was suggested that metipranolol and exaprolol are nonselective beta-adrenoceptor antagonists, similarly as propranolol, whereas BL 445 shown some beta 1-selectivity. In contrast to their antagonistic effects on the membrane activities and muscle tension, both histamine and isoprenaline increased the level of cAMP in smooth muscle cells and, when present simultaneously, their effect was additive. The mechanism of histamine-induced cAMP level elevation and the possible involvement of different subcellular compartments in the action of isoprenaline and histamine in relation to the contraction-relaxation cycle is discussed.

Adrenergic alpha-Agonists↗
PubMed1987

The effect of local anaesthetics on noncholinergic-nonadrenergic (NCNA) responses of the gut.

The newly synthesized carbamate local anaesthetics (heptacaine and BK-141) affected the NCNA responses of different segments of the guinea-pig small (jejunum, ileum) and large (colon, taenia coli) intestine in a similar manner to the classic local anaesthetics (procaine and trimecaine). The sensitivity of NCNA responses to the action of local anaesthetics was, in order: primary contraction greater than rebound contraction greater than primary relaxation. The action of the carbamate local anaesthetics resembled that of trimecaine more than that of procaine. The results presented suggest that different Ca2+ channels participate in primary and rebound contraction and that local anaesthetics affect the receptor-operated Ca2+ channels in lower concentrations than the voltage-dependent ones.

Action Potentials↗
PubMed1986

Effect of desensitization induced by adenosine 5'-triphosphate, substance P, bradykinin, serotonin, gamma-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.

Adenosine Triphosphate↗
PubMed1986

Localized thyroid plasmacytoma.

Two cases of localized thyroid plasmacytoma are described and the literature is reviewed. In most cases the tumors arise in thyroid glands with lymphocytic thyroiditis. Thyroidectomy with regional lymph node biopsy seems to be the initial treatment of choice. Postoperative irradiation appears to be indicated in cases with residual thyroid tissue remaining and in those with documented regional nodal involvement.

Aged↗
PubMed1986

Evidence that sensory neurons participate in the non-cholinergic, non-adrenergic contractile response of the guinea-pig ileum.

The possible role of non-cholinergic, non-adrenergic (NCNA) nerves in responses of the guinea-pig terminal ileum to transmural nerve stimulation (TNS) and that of sensory nerves in NCNA responses were investigated. The action of acetylcholine was almost abolished in the presence of histamine, whereas the contractions elicited by TNS were changed to frequency-dependent contraction followed by a secondary relaxation. Guanethidine did not alter the contractions or secondary relaxations. Atropine abolished the action of acetylcholine and transiently suppressed the responses to low (up to 2 Hz) and attenuated (by about 50%) those to high (4 to 20 Hz) frequency stimulation. The remaining complex NCNA response was the sum of the excitatory and inhibitory responses. During desensitization to capsaicin, and in its presence, the NCNA contractions were reduced, whereas the relaxations were not significantly enlarged. The present results suggest that besides the cholinergic innervation, the excitatory and inhibitory NCNA innervation also participates in the responses of the guinea-pig ileum to TNS even without suppression of cholinergic and adrenergic transmission, and that the sensory nerves are, at least to some extent, involved in the NCNA excitatory response.

Animals↗
PubMed1986

The non-adrenergic non-cholinergic innervation and transmission in the small intestine.

An attempt has been made to summarize the present knowledge on the non-adrenergic non-cholinergic (NANC) transmission in the small intestine. The paper presents old and recent findings as well as the author's own results on the basic characteristics of the NANC mechanical and membrane potential changes. Further the sensitivity of NANC transmission to different influences, such as elevation or reduction of the muscle tension and membrane potential level, drug actions, desensitization of receptors, etc. are elucidated. The nature of the putative NANC neuromediator/s (purines, peptides, etc.) in the small intestine is discussed.

Adenine Nucleotides↗
PubMed1986

The effects of some carbamate local anaesthetics on the guinea-pig ileum.

The action of some carbamate local anaesthetics, pentacaine, BK-52 and heptacaine, was compared in the guinea-pig ileum with that of classic local anaesthetics, procaine and trimecaine. Contractions of the ileum were evoked by transmural stimulation, nicotine, acetylcholine, noradrenaline, histamine, K+ and Ba++. Although the evoked contractions were inhibited by all the local anaesthetics, there was a marked difference in their ability to influence the smooth muscle activation induced by different stimuli. The differences among the IC50 values were slight in the case of pentacaine, moderate in the case of trimecaine and BK-52 and large in the case of procaine and heptacaine. It is suggested that besides their effects on the unmyelinated autonomic nerves, the carbamate local anaesthetics studied can also affect the smooth muscle membrane, similarly to the classic agents. The mechanism of their direct effect is discussed.

Anesthetics, Local↗
PubMed1986

Carbamate-induced rhythmic activity in the guinea-pig ileum.

The action of newly synthesised basic esters of alkoxy-substituted derivatives of phenylcarbamic acid was compared with that of procaine and trimecaine in the guinea-pig small intestine. Some of the carbamate local anaesthetics, in concentrations high enough to markedly suppress cholinergic twitches, elicited regular rhythmic activity of the guinea-pig ileum. This effect of the carbamates was dependent on the position of the alkoxysubstituent and was independent of the basic group (pyrrolidine, piperidine or perhydroazepine) present. Only the ortho-substituted derivatives were active. It was also found that the rhythmic activity evoked was of myogenic origin, produced by rhythmic undulations of the sodium-pump activity, accompanied by a potential-dependent change in Ca2+ permeability. It is suggested that the mechanism by which carbamates reveal this endogenous rhythm in the guinea-pig ileum could be a selective block of noncholinergic, nonadrenergic innervation or the TEA-like activity of carbamates.

Anesthetics, Local↗
PubMed1986

The effect of carbamate local anaesthetics on vascular smooth muscle.

The effect of carbamate local anaesthetics (pentacaine and heptacaine) on contractile responses induced by transmural nerve stimulation, exogenous noradrenaline (NA) and KCl, as well as on noradrenaline-induced Ca2+ mobilization, were investigated in isolated rabbit blood vessels under isometric conditions. Pentacaine and heptacaine inhibited the neurogenic contractions and those elicited by exogenous NA and KCl. The neurogenic contractions were more sensitive to the local anaesthetics than those evoked by exogenous NA. The onset of inhibition was slow and developed gradually. This inhibition was concentration-dependent and continued for several hours in spite of repeated washings of the vessels. Pretreatment of the vascular preparations with pentacaine and heptacaine reduced NA- and Ca2+-induced contractions in Ca2+-free K+-depolarizing solution. The Ca2+-contracted vessels were also relaxed by the anaesthetics studied. It is suggested that carbamate local anaesthetics inhibit not only neuronal conductance but also Ca2+ entry into the vascular smooth muscle cells and NA-induced release of intracellular Ca2+.

Anesthetics, Local↗
PubMed1985

Effects of 3,4-diaminopyridine and tetraethylammonium on the pre- and post-junctional alpha-adrenoceptor mediated inhibitory actions of noradrenaline in the guinea-pig ileum.

The effects of potassium channel blockers, 3,4-diaminopyridine (DAP) and tetraethylammonium (TEA) were studied on the pre- and post-junctional alpha 2-adrenoceptor mediated effects of noradrenaline in the guinea-pig proximal ileum. Both DAP (4 to 500 mumol l-1) and TEA (0.3 to 3 mmol l-1) transiently increased the basal tension of the ileum. However, DAP also increased the amplitude of the smooth muscle twitches evoked by transmural nerve stimulation, whereas TEA marginally depressed them. Atropine (2 mumol l-1) antagonized the contractions induced by DAP but did not affect the similar effects of TEA. On the other hand, DAP restored the smooth muscle twitches depressed by atropine, while TEA did not. DAP, in a concentration-dependent manner, reduced or abolished the prejunctional inhibitory alpha 2-adrenoceptor mediated effect of noradrenaline, whereas TEA (up to 3 mmol l-1) was almost ineffective. The postjunctional inhibitory alpha 2-adrenoceptor mediated effect of noradrenaline was attenuated even at the smallest TEA concentration used (0.3 mmol l-1) and its postjunctional stimulatory alpha 1-adrenoceptor mediated effect was unmasked. However, DAP, was only marginally effective, even at the highest concentrations used (100 and 500 mumol l-1). From these results it would appear that in both the pre- and post-junctional inhibitory alpha 2-adrenoceptor mediated actions of noradrenaline in the guinea-pig ileum the primary step might be an increased potassium conductance. However, the potassium channels on the neuronal and the smooth muscle membrane have different sensitivities to DAP and TEA.

4-Aminopyridine↗