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Biomedical subjects

O Kadlec

Publications and source records attributed to O Kadlec.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1984

Smooth muscle stimulation by an immunomodulatory compound muramyl dipeptide: does it involve serotoninergic system?

Contractions evoked by muramyl dipeptide (MDP), a synthetic compound possessing immunostimulatory properties, were studied in several isolated nerve-smooth muscle preparations. The contractions by micromolar concentrations of MDP were evoked either by direct interaction with smooth muscle (rat stomach strip) or at least partly indirectly via neurogenic stimulation (guinea pig ileum); the effect was stereospecific since the MDP-D was not active. The insensitivity of the preparations to serotonin (5-HT), either inherent (vas deferens) or after 5-HT antagonists or after desensitization to 5-HT, prevented or markedly reduced the contractile activity by MDP. On the other hand, a nanomolar concentration of MDP enhanced the sensitivity of the rat stomach strip to 5-HT.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1984

An interaction of endogenous and exogenous opiates in the guinea-pig isolated ileum.

In the myenteric plexus-longitudinal muscle preparation of the guinea-pig ileum an interaction of exogenously applied opiates with posttetanic inhibition was studied. The electric tetanic stimulation (30 Hz) evoking the release of endogenous opioids resulted in an inhibition of neurogenic cholinergic twitch contractions (0.1 Hz) of the same preparation. This posttetanic inhibition was largely attenuated or even reversed into potentiation if tested in the presence of ketocyclazocine (40 nmol/l) or pentazocine (0.3 and 3 mumol/l) and also methionine-enkephalin (0.2 and 2 mumol/l) or morphine (1 mumol/l) while it was not affected in the presence of leucine-enkephalin (2 mumol/l) or D-Ala2-D-Leu5-enkephalin (40 and 400 nmol/l). An involvement of kappa- and mu-opiate receptors in the action of the endogenous mediator(s) of posttetanic inhibition is suggested.

Acetylcholine↗
PubMed1983

Posttetanic potentiation at the neuromuscular junction of the guinea-pig ileum longitudinal muscle strip: influence of calcium, temperature, ouabain and hexamethonium.

The effect of tetanic stimulation on the twitch responses of the longitudinal muscle-myenteric plexus preparation of the guinea-pig ileum was investigated. In the presence of naloxone plus indomethacin twitch contractions following tetanus were potentiated. This posttetanic potentiation (PTP) of twitches was absent after reducing calcium concentration (0.6 mmol/l) in the bath or lowering bath temperature (22 degrees C); doubling calcium concentration (5 mmol/l) enhanced PTP. The addition of ouabain (0.8-5 mumol/l) prevented PTP; following the washout of ouabain the time course of PTP was prolonged. Hexamethonium (0.5 mmol/l) did not prevent PTP. The results suggest that similarly to the situation at nicotinic synapses of the striated muscle the mechanism of PTP at this muscarinic synapse might be associated with changes in calcium distribution. Moreover, the effect of ouabain might suggest the importance of electrogenic sodium pumping from and hyperpolarization of cholinergic nerve terminals after tetanus.

Animals↗
PubMed1982

The analysis of post-tetanic potentiation in guinea-pig ileum longitudinal muscle strip.

The effect of tetanus on the twitch responses of the longitudinal muscle-myenteric plexus preparation of the guinea-pig ileum to electrical stimuli was investigated in the presence of naloxone and indomethacin. Naloxone was used to prevent post-tetanic twitch inhibition due to the release of endogenous opiate ligands, and indomethacin to diminish pretetanic twitch height. Twitch contractions following tetanus were potentiated in the presence of both drugs. The optimal stimulation parameters for the manifestation of post-tetanic potentiation (PTP) were determined; tetanic stimulation: 30 Hz for 25 s. supramaximal impulse intensity; twitches: 0.04 Hz, low impulse intensity. PTP was also obtained when indomethacin was replaced by noradrenaline or adenosine, i.e. by drugs whose mechanism of action also includes a presynaptic effect. Postsynaptic changes in contractility cannot fully account for the observed PTP of twitches judging from the smaller effect of tetanus on acetylcholine-evoked contractions. The hypothesis of a presynaptic origin of PTP at this muscarinic synapse was corroborated in the experiments where acetylcholine stores were labelled with [3H] choline and the release of the label was increased during PTP. Furthermore, a bioassay showed that the output of endogenous acetylcholine in the post-tetanic interval was increased in the presence of naloxone plus indomethacin but not in their absence. The fact that PTP was also observed in the absence of any drug, if the tetanic stimulation was short (10 s) and of low impulse intensity, suggested its possible physiological significance.

Acetylcholine↗
PubMed1981

Posttetanic inhibition in the guinea - pig ileum by endogenous opiate ligands; effects of cold storage of the preparations and of the age of experimental animals.

Naloxone-sensitive inhibition of neurogenic twitch contractions was induced by tetanic stimulation of the myenteric plexus-longitudinal muscle preparation of the guinea-pig ileum. In preparations stored in the cold for more than 2 days, the inhibition disappeared and in some preparations posttetanic potentiation was manifested, instead. Thus enkephalinergic neurones are more sensitive to the effect of cold storage than cholinergic neurones. The naloxone-sensitive posttetanic inhibition was developed in newborn animals but in animals older than 3 years a naloxone-resistent component appeared.

Acetylcholine↗
PubMed1979

Post-tetanic potentiation in the innervated smooth muscle preparation of the guinea-pig ileum.

The phenomenon of posttetanic potentiation of electrically evoked twitch contractions in the myenteric plexus-longitudinal muscle of the guinea-pig ileum was observed when (1) post-tetanic inhibition had been prevented by naloxone, an opiate receptor antagonist, and (2) the twitches had been diminished by indomethacin, an inhibitor of prostaglandin synthesis. The origin of posttetanic potentiation at this muscarinic synapse appeared to be presynaptic.

Acetylcholine↗