Biomedical subjects

O Kadlec

Publications and source records attributed to O Kadlec.

At least 19 recordsLinked to original sources

PubMed1993

The topographical basis and frequency-dependence in the effect of different compounds on neurogenic contractions of the guinea-pig ileum.

The site of action of compounds affecting either Na+/K+ or Ca2+ conductances in nerve terminals was studied in myenteric plexus-longitudinal muscle strips from the guinea-pig ileum. A preparation in a special triple bath was drawn through two rubber membranes, dividing a strip into three segments. Neurogenic stimulation of the oral segment, set up nerve action potentials in the neurons projecting axons up to the aboral segment. These axons, turning into varicose nerve terminals, conducted action potentials aborally across the middle segment (10 mm). Finally, the nerve terminals, extending into the aboral segment, might be also invaded and trigger aboral twitches. Compounds were added, either to the oral segment, to affect the genesis and spread of action potentials in the proximal parts of cholinergic neurons (cell bodies): or they were added to the middle segment to affect propagation of action potentials in axon preterminals and the proximal parts of varicose nerve terminals; or they were added to the aboral segment to affect the propagation in the endings of varicose nerve terminals. As a result, the amplitude of aboral twitches reflected drug effects at each site quantitatively. Interference with Na+/K+ conductance by an elevation of K+ concentration or by cisapride or neuropeptide Y at non-aboral segments modulated the amplitude of aboral twitches evoked by low-frequency stimulation but did not affect post-tetanic potentiation of twitches; on the other hand, changes in Ca2+ concentration of compounds affecting excitatory amino acids receptor system or omega-Conotoxin, when applied to the aboral segment, affected post-tetanic potentiation. Thus the effects of cisapride and neuropeptide Y (NPY) during low-frequency stimulation could be located to axon preterminals or the proximal parts of the terminals and their polarization. On the other hand, a new role for glutamatergic system in post-tetanic potentiation was bound to the endings of varicose nerve terminals with Ca-sensitive component in conduction.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1991

An attempt to localize the site of action of different agents within cholinergic motor neurones of the myenteric plexus-longitudinal muscle preparation of the guinea pig ileum by the triple bath method.

The site of action of cholinergic, adrenergic, peptidergic and opioid agents was studied in myenteric plexus-longitudinal muscle strips from the guinea pig ileum. A preparation in a special triple bath was drawn through two rubber membranes, dividing the strip into three segments. Neurogenic stimulation of the oral segment, set up nerve action potentials also in the neurones projecting axons up to the aboral segment. These axons, turning into varicose nerve terminals, conducted action potentials aborally across the middle segment, that was up to 10 mm wide. Finally, the nerve terminals, extending into the aboral segment, might be also invaded triggering twitches. Agents were added, either to the oral segment, to affect the genesis and spread of action potentials in the proximal parts of cholinergic neurones (cell bodies, axon hillocks, initial segments and axon preterminals) or they were added to the middle segment to affect propagation of action potentials in varicose nerve terminals. As a result, the amplitude of aboral twitches reflected their effects at each site, quantitatively. Noradrenaline and ethylketocyclazocine were more effective at the site of varicose nerve terminals, whereas substance P, acetylcholine and oxotremorine were more effective at the proximal parts; pilocarpine and nicotine were effective at both sites. Changes in membrane polarization might be the final common effect in the mechanism of action of all the stimulatory agents used.

Action Potentials↗

PubMed1991

Non-synaptic cholinergic modulation of neurogenic twitches of the guinea-pig ileum.

The effect of cholinergic and anticholinergic compounds on conduction of neuronal excitation has been studied in myenteric plexus-longitudinal muscle strips from the guinea-pig ileum. A preparation in a special triple bath was drawn through two rubber membranes dividing the strip into three segments. Neurogenic stimulation of the oral segment set up nerve action potentials propagating aborally across the middle segment (10 mm) so that the aboral segment might be also invaded, eventually. Drugs were added to the middle segment to affect neuronal propagation (non-synaptic effects) which was monitored by twitch height of the aboral segment. The application of acetylcholine to the middle segment augmented aboral twitches. The effects of nicotine, pilocarpine and oxotremorine were selectively blocked by (+)-tubocurarine, pirenzepine and atropine, respectively. The effect of acetylcholine was suppressed by pirenzepine and atropine and mimicked by doubling of KCl concentration. The effect of acetylcholine may be thus explained by the facilitated propagation of nerve action potentials in partially depolarized cholinergic terminals via stimulation of muscarinic receptors. The adenylate cyclase system is not directly involved in the mechanism of muscarinic facilitation of neuronal propagation in the terminals; however, it may participate in the modulation of a final common effector mechanism.

Acetylcholine↗

PubMed1991

[Characteristics of the aged surgery patient].

In 32 old people selected at random (16 men and 16 women) indicators of the water and mineral salt balance were investigated as well as renal and hepatic functions, nutritional status, serum insulin, thyroxine and triiodothyronine and in 12 also changes after operation. The findings indicate that it is necessary to ensure clinical and biochemical monitoring as well as proper preparation of old people for a planned surgical operation. Old people must be always considered critical patients and it is important to provide extra preoperative and postoperative care.

Aged↗

PubMed1990

[Nitric oxide--a new and nontraditional transmitter].

NO is obviously identical with the relaxation factor produced by the vascular endothelium (EDRF) and is also the substance responsible for some other biological activities. It is formed in the organism from L-arginine by the action of the enzyme NO synthetase. The main mechanism of action is the activation of the enzyme guanyl cyclase and the result is an increase of the intracellular level of cyclic guanyl monophosphate. Depending on the type of effector cell, either vasodilatation occurs and adhesion is inhibited and the blood platelets coagulate or the cytotoxicity of macrophages increases. With the development of new, more effective inhibitors of NO synthetase there is also the possibility to study the physiological importance of NO in more detail. These new discoveries provide a more profound biochemical and pharmacological basis and perhaps also new indications or preventive possibilities of the known treatment of vascular spasms by nitroderivatives; moreover, there is the possibility to seek new ways in the anti-tumourous and antimicrobial treatment and elsewhere.

Animals↗

PubMed1990

The topographical basis of cholinergic transmission in guinea-pig ileum myenteric plexus.

Myenteric plexus-longitudinal muscle strips were used to study nerve action potential propagation and transmission and their differences between the proximal and the distal regions of cholinergic terminals. Neurogenic twitches of a portion of the strip were evoked by focal electrical stimulation. Twitches mediated by the distal regions of cholinergic nerve terminals were more influenced by drugs affecting Ca2+ "utilization" (Bay K 8644, kappa opiate ligand ethylketocyclazocine, changes in extracellular Ca2+ or Co2+ concentration) in contrast to twitches mediated by proximal regions of these terminals which were more influenced by drugs affecting sodium-potassium spike (tetrodotoxin, dendrotoxin, 4-aminopyridine, tetraethylammonium). Post-tetanic potentiation of twitches was prominent with that portion of the strip where the distal regions of nerve terminals were involved. Drugs interfering with Na+/K+ spikes indiscriminately influenced both the twitch height and post-tetanic potentiation whereas changes in extracellular Ca2+ concentration affected selectively only post-tetanic potentiation. Release of [3H]acetylcholine from pre-labelled strips evoked by 1 Hz continuous stimulation or by train stimulation at 30 Hz was measured selectively from portions containing either proximal and distal or only distal regions of nerve terminals. The release from portions containing the distal regions was relatively higher when evoked by 30 Hz than by 1 Hz. The distal regions of nerve terminals might be thus recruited to participate in transmission by a frequency-dependent process. Nerve impulses were recorded from strands of nerve fibres in the myenteric plexus. At 1 and 5 mm distance from the stimulation focus nerve impulses were completely suppressed by tetrodotoxin. At 5 mm, in some strands the amplitude of nerve impulses was also subject to the effect of drugs affecting Ca2+ "utilization"; facilitation of nerve impulse amplitude during 30 Hz train stimulation was always influenced by drugs affecting Ca2+ "utilization". Propagation of nerve impulses in the distal region of cholinergic nerve terminals was found to be Ca-sensitive and frequency-dependent; this might form the basis for facilitation and post-tetanic potentiation of muscarinic transmission.

Acetylcholine↗

PubMed1990

Non-junctional modulation of neurogenic twitches of the guinea-pig ileum by some peptides and other compounds in the triple bath.

The effects of some neuropeptide transmitter candidates and of some other neurotoxins or drugs on conduction of neural excitation were studied in myenteric plexus-longitudinal muscle strips from the guinea-pig ileum. A preparation in a special triple bath was drawn through two rubber membranes dividing the strip into three segments. Neurogenic stimulation of the oral segment set up nerve action potentials propagating aborally across the middle segment so that the aboral segment might also be invaded. Drugs were added to the middle segment to affect neuronal propagation (non-junctional effects) which was monitored by twitch amplitude of the aboral segment. The application of bradykinin and cromakalim did not affect aboral twitches although strong contractile and relaxatory effects were observed when the drugs were applied directly to the aboral segment; no neurogenic effects thus manifested. Capsaicin and neurotensin, when applied both to the middle and aboral segments, elevated the tone of the preparations accompanied with a decrease in twitch amplitude; these effects may have been due to neurogenic stimulation and release of other motor neurotransmitters. The application of VIP, apamin and dendrotoxin to the middle as well as to the aboral segments augmented aboral twitches, which might be at least partly due to facilitation of nerve action potential propagation in nerve terminals of cholinergic motor fibres.

Action Potentials↗

PubMed1990

[A rational diagnostic program for hypertension in children].

Early screening of subjects liable to develop cardiovascular diseases is one of the main tasks of preventive cardiology of child age. The authors present a rational programme for the screening and diagnostic of hypertension in children, its aim being to differentiate primary and the most frequent secondary forms of hypertension; this will create prerequisites for its adequate treatment (non-pharmacological and pharmacological) as well as for dispensarization. Review.

Adolescent↗

PubMed1989

Interactions of neurogenic responses of longitudinal and circular muscle in the guinea-pig ileum.

The relationship between neurogenic responses of longitudinal and circular muscle was studied by measuring contractions and EMG or nonadrenergic, non-cholinergic (NANC) relaxations and NANC inhibitory junction potentials in different preparations of the guinea-pig ileum. NANC relaxation of longitudinal muscle was observed also without any preceding or concomitant circular muscle contraction ruling out the possibility that the latter might be the cause of the NANC relaxation. Circular muscle twitches or powerful contractions were absent if there was no preceding neurogenic or myogenic excitation of longitudinal muscle; in preparations with myenteric plexus-longitudinal muscle layers removed only small residual responses were seen although still under neurogenic influences. Thus excitation of longitudinal muscle seemed a prerequisite for synchronized and powerful contractions of circular muscle to occur. Cholinergic contraction and NANC relaxation of longitudinal muscle evoked by field stimulation were partly inhibited if the submucous plexus was also present suggesting the involvement of a more complex neuronal circuitry in these responses.

Adenosine Triphosphate↗

PubMed1987

The topography of cholinergic transmission in the mechanism of drug action at muscarinic synapses of the guinea-pig ileum.

The pharmacology of cholinergic neurogenic responses evoked by the participation of only the endings of axon terminals was compared to that of responses evoked by participation of the more proximal parts of the terminals also. Myenteric plexus-longitudinal muscle strips of the guinea-pig ileum were drawn through narrow orifices in 2 rubber membranes dividing a bath into 3 separate compartments. Oral segments were stimulated electrically by single impulses or by trains and local neurogenic contractions were evoked. The contractions of the aboral segment due to nerve impulses transmitted from the oral segment via the middle segment were also recorded. The opioid ligands ketocyclazocine and [D-Ala2,MePhe4,Met(O)5-ol]enkephalin and noradrenaline inhibited the twitches of the aboral segment evoked by oral segment stimulation more than the local twitches of the oral segment when these agents were applied directly to the respective compartments. The twitches of the aboral segment were also inhibited by the application of these drugs into the middle compartment adjusted to 10 mm width. Verapamil and the alkaline earth metal ions cobalt and lanthanum had similar effects. 4-Aminopyridine increased twitch amplitude more in the aboral segment than in the oral segment when applied directly; similar effects in the aboral segment were seen when the agents were applied to the middle compartment. The action of atropine, papaverine, d-tubocurarine and prostigmine did not discriminate between twitches in the oral and aboral segment when applied directly and all drugs except prostigmine were without effect when applied to the middle compartment.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1987

Role of substance P in post-tetanic potentiation in myenteric plexus-longitudinal muscle preparations; the effect of substance P-antagonist.

A role of substance P in post-tetanic potentiation in the myenteric plexus-longitudinal muscle preparation of the guinea-pig ileum was investigated by means of substance P-antagonist, (D-Pro2, D-Trp7,9)-substance P. After the addition of substance P-antagonist (10(-7)-10(-5) mol x l-1) a dose-dependent reduction of post-tetanic potentiation of neurogenic twitches was observed. Post-tetanic potentiation was actually abolished in the presence of 10(-5) mol x l-1 substance P-antagonist. It has been shown previously by our group that post-tetanic potentiation is reduced in preparations desensitized by substance P; this, together with our present results supported the hypothesis that the release of substance P-like compounds during tetanic stimulation played a key role in the mechanism of post-tetanic potentiation.

Animals↗

PubMed1987

The topography and dynamics of cholinergic transmission in the myenteric plexus-smooth muscle preparation of the guinea-pig ileum; the effect of ketocyclazocine, a kappa opiate ligand.

Output of acetylcholine (ACh), neurogenic electromyogram (NEMG) and contractions of guinea-pig ileum preparations were studied during stimulation by high-frequency trains of impulses. Under control conditions the output of ACh per impulse after 2nd to 4th impulses during train stimulation (30 Hz) was higher by 20-40% than the level of ACh output during the first impulse. In the presence of ketocyclazocine (KTZ, 80 nmol x l-1) the output of ACh evoked by the first impulse was more effectively inhibited than that after impulses 2 to 4 so that the increase was higher (80-170%). NEMG, a direct consequence of the localized action of released transmitter (ACh), was recorded in the longitudinal muscle 4 and 10 mm aborally from the focal stimulation site. The incidence of NEMG responses was higher at the proximal than at the distal site and was proportional to the number of impulses in a train (100 Hz). At the distal site KTZ suppressed the appearance of NEMG responses to single impulses whereas at the proximal site its effect was much less; and so was its effect at either site during train stimulation. It is concluded that in the course of train stimulation, sites of transmission more distant from the stimulation focus were recruited, and consequently the secretion of ACh in succeeding impulses was enhanced. KTZ might preferentially inhibit the propagation of excitation by the very first impulse.

Acetylcholine↗

PubMed1986

Interactions between the duration of stimulation and noradrenaline on cholinergic transmission in the myenteric plexus-smooth muscle preparation.

Output of acetylcholine (ACh), electromyogram (EMG) recordings and contractions of myenteric plexus-longitudinal muscle strip preparations from the guinea-pig ileum were studied during stimulation by single impulses or by trains (30 Hz; 2 to 128 impulses) under control conditions and in the presence of noradrenaline (NA). During supramaximal stimulation NA (2.5 microM) inhibited both contractions of the smooth muscle and the release of ACh evoked by single impulses more effectively than those evoked by train stimulation so that in a train of 4 impulses the output of ACh per impulse after the 2nd to 4th impulses was 69 to 104% higher than the output after the 1st impulse. During submaximal stimulation, contractions and ACh release evoked by single impulses were almost completely inhibited by NA. The neurogenic EMG, a direct consequence of the localized action of released transmitter (ACh), was recorded in the longitudinal muscle 4 and 10 mm aborally from the focal stimulation site. The incidence of the neurogenic response was much higher at the proximal (4 mm) than at the distal (10 mm) site and was proportional to the number of impulses in a train (100 Hz). NA inhibited propagation of the neurogenic response evoked by single impulses whereas its effect during train stimulation was less. It is concluded that in the course of train stimulation, sites of transmission more distant from the stimulation focus was recruited, and consequently the secretion of ACh in succeeding impulses was enhanced. NA could interfere with this process; it might inhibit the invasion by action potentials of cholinergic nerve terminal varicosities, thereby reducing the release of ACh.

Acetylcholine↗

PubMed1986

The influence of immune status on the in vitro sensitivity of serotoninergic receptors in the rat stomach strip.

Serotoninergic contractions of the rat stomach strip were evoked and EC50 determined. In preparations from control animals MDP, 50 mumol/l, decreased EC50 or sensitized the preparation. In the strips from animals where adjuvant arthritis was induced, higher sensitivity to 5-HT was observed and the sensitizing effect of MDP was retained. In the strips from animals pretreated with cyclophosphamide or in the terminal stage of tumor growth lower sensitivity to 5-HT, which could be further decreased by MDP, were noticed. These opposite effects in serotoninergic reactions were tentatively linked with the modulation of the immune status in vivo.

Acetylmuramyl-Alanyl-Isoglutamine↗

PubMed1985

How far from the stimulation site in myenteric plexus-longitudinal muscle preparations the neurogenic cholinergic contraction can be evoked?

Neurogenic contractions of a segment of myenteric plexus-longitudinal muscle strip preparations from the guinea-pig ileum were evoked. The site of electric stimulation was separated from the contracting segment by a gap preventing the spread of muscle action potentials set up in other regions. The width of the separating gap (2-20 mm) indicated the length of nerve fibers that could conduct impulses across and trigger cholinergic contractions behind the gap; it was more than 12 and less than 16 mm. Transmission of excitation was more effective in the aboral direction compared to the oral direction and was not apparently affected by noradrenaline nor by substance P.

Animals↗

PubMed1984

The topography of posttetanic potentiation in guinea-pig ileum.

The myenteric plexus-longitudinal muscle preparation of the guinea-pig ileum offers, by its anatomical arrangement, the possibility of studying a new aspect of posttetanic potentiation (PTP); its topography. Evidence was sought and obtained that during PTP more distal junctional sites of cholinergic nerve terminals may be recruited into the transmitter secretion process.

Acetylcholine↗

PubMed1984

Post-tetanic potentiation at the nerve-muscle junction in the longitudinal muscle of the guinea-pig ileum. Possible role of substance P.

The effect of short tetanic stimulation (30 Hz for 25 s) on the following twitch responses of the myenteric plexus-longitudinal muscle preparation of guinea-pig ileum to electric stimulation (0.1 Hz) was investigated in the presence of naloxone and indomethacin. Post-tetanic potentiation (PTP) of the twitches observed in control experiments was abolished in preparations desensitized by substance P but it was not affected in preparations desensitized by serotonin or pretreated with methysergide. Immediately after 5 min tetanic stimulation a decreased sensitivity to substance P but unchanged sensitivity to serotonin were observed. Electromyogram (EMG) of the longitudinal muscle layer was picked up 4 and 10 mm aborally from the stimulation site in response to 1 to 16 impulse trains delivered at 100 Hz. In control conditions only the longer trains triggered this neurogenic response at the distal recording site. In the presence of substance P but not serotonin facilitation occurred so that the distal site was frequently recruited to respond with an EMG even to single impulses. A substance P-like compound rather than serotonin may be a candidate for the neuromodulator or neurotransmitter substance involved in PTP and changes in the response topography of muscarinic transmission.

Animals↗

PubMed1984

Possible role of prostaglandins in post-tetanic potentiation at the nerve-muscle junction in the longitudinal muscle strip of guinea-pig ileum.

The effect of tetanic stimulation on the twitch responses of the longitudinal muscle-myenteric plexus preparation of the guinea-pig ileum to electrical stimulation was investigated in the presence of naloxone. Under this condition, or after the addition of PGE2, twitch contractions were maximal and no potentiation of twitches following tetanus was observed. In the presence of indomethacin (1 mumol litre-1) twitches were diminished and post-tetanic potentiation (PTP) was manifested. PTP was seen with indomethacin concentrations of 1 to 20 mumol litre-1 or after simultaneous addition of diphloretin phosphate (16 mumol litre-1). Thus it seems unlikely that the effect of prostaglandins released during tetanic stimulation would be of key importance for the manifestation of PTP. Rather it is thought that a decrease in the release of acetylcholine from motor nerve terminals, and consequently smaller twitches in the presence of indomethacin, offer favourable conditions for PTP.

Acetylcholine↗