Biomedical subjects

M Papasova

Publications and source records attributed to M Papasova.

At least 19 recordsLinked to original sources

PubMed2000

Nitric oxide modulates release of noradrenaline in guinea-pig gastric fundus.

The interaction between nitric oxide (NO) and the release of [(3)H]noradrenaline ([(3)H]NA) in conditions of non-activated and activated nicotinic receptors in guinea-pig gastric fundus preincubated with [(3)H]NA was studied. Nicotinic receptor agonist, 1,1-dimethyl-4-phenyl-piperazinium iodide (DMPP) (100 microM) significantly increased the resting release of [(3)H]NA. NO-synthase inhibitor, N(omega)-nitro-L-arginine (L-NNA) (100 microM) significantly decreased DMPP-induced release of [(3)H]NA. Field electrical stimulation (FES) (2Hz; 1 ms; 360 st) significantly increased the release of [(3)H]NA above the basal levels. L-NNA significantly decreased the stimulation-evoked release of [(3)H]NA. DMPP increased the stimulation-evoked release of [(3)H]NA, effect which was significantly decreased by L-NNA. The data suggests that endogenous NO increases the release of [(3)H]NA, evoked either by activation of the nicotinic receptors or by electrical stimulation in guinea-pig gastric fundus.

Animals↗

PubMed1999

Nitric oxide (NO) increases acetylcholine release from and inhibits smooth muscle contraction of guinea-pig gastric fundus.

Experiments were carried out to investigate the interaction between nitric oxide (NO) and cholinergic neurotransmission in smooth muscle strips of guinea-pig gastric fundus. Electrical field stimulation (2 Hz, 1 ms, 360 shocks) evoked atropine-sensitive contractions. Dimethylphenylpiperazinium (DMPP) (100 microM), a nicotinic receptor agonist, reversed the stimulation-evoked contraction and resulted in relaxation. Nomega-nitro-L-arginine (L-NNA) (100 microM), an NO synthase inhibitor, significantly increased the amplitude of stimulation-evoked contraction and abolished the effect of DMPP. Electrical stimulation increased the release of [3H]acetylcholine ([3H]ACh) from the tissue strips above the basal levels. Neither L-NNA (100 microM) nor DMPP (100 microM) alone influenced the basal release of [3H]ACh. Nomega-nitro-L-arginine (100 microM) decreased the electrical stimulation-evoked release of [3H]ACh. Dimethylphenylpiperazinium increased the stimulation-evoked release of [3H]ACh but had no effect in the presence of L-NNA. It is suggested that in guinea-pig gastric fundus, endogenous NO released in response to field stimulation has an opposite effect at the pre- and postsynaptic sites: it increases the release of ACh from cholinergic nerve terminals but reduces smooth muscle responses to ACh.

Acetylcholine↗

PubMed1998

Involvement of nitric oxide in extrinsic nervous control of ileal contractile activity.

The experiments were carried out on guinea pig mesenteric nerve-ileal preparations (ileal segments with mesenteric nerves originating from the superior mesenteric ganglion) isolated at various distances from the ileocecal junction (ICJ). Contractile activity was recorded in the presence of hexamethonium (50 microM). On the background of electrical field stimulation (EFS; 0.1 Hz, 0.5 ms, supramaximal current intensity)-induced twitch contractions, the mesenteric nerve stimulation (MNS; frequency of 2-30 Hz, 0.5 ms, supramaximal current intensity, 20-s trains) exerted two types of effects, depending on the distance from ICJ at which the preparations were isolated and on the pulse frequency. In preparations isolated from the ileum at a distance of 20 cm from ICJ, MNS at all the frequencies studied inhibited the EFS-induced twitch contractions, reaching the maximum at 30 Hz. In preparations isolated from the terminal ileum at a distance of 10 cm from ICJ, MNS at 20 Hz and 30 Hz decreased the twitch contraction amplitude, whereas MNS at 2-10 Hz produced an increase in the tone on which twitch contractions with reduced amplitude were superimposed. The finding that guanethidine (5 microM) eliminated the MNS twitch inhibition provides evidence for the adrenergic origin of the latter. The nitric oxide synthase inhibitor Nomega-nitro-L-arginine (100 microM) was efficient in reducing the MNS twitch inhibition but only at low-frequency (5 Hz) MNS (p < 0.05). Our results suggest the participation of nitric oxide in the nervous control exerted by the superior mesenteric ganglion over the ileal contractile activity.

Animals↗

PubMed1998

Role of different bombesin receptor subtypes mediating contractile activity in cat upper gastrointestinal tract.

Mammalian bombesin-like peptides, gastrin-releasing peptide (GRP) and neuromedin B (NMB) are known to increase the motility of different segments in the gut. The present study was carried out to identify the bombesin receptor subtypes mediating the contractions induced by exogenous bombesin-like peptides in muscle strips isolated from cat esophagus, fundus, and duodenum. Both GRP-10 and NMB evoked concentration-dependent contractions in circular strips of esophagus and fundus and in longitudinal strips of the duodenum. These contractions were tetrodotoxin- and atropine-resistant. The potency of NMB in esophageal strips was 33 times higher than that of GRP-10. The NMB-preferring receptor antagonists D-Nal-Cys-Tyr-D-Trp-Lys-Val-Cys-Nal-NH2 (SSocta) and D-Nal-cyclo[Cys-Tyr-D-Trp-Orn-Val-Cys]-Nal-NH2 (BIM-23127) shifted the NMB and GRP concentration-response curves to the right, while the GRP-preferring receptor antagonist [D-Phe6]Bombesin(6-13)-methyl-ester (BME) did not affect the response to the peptides. Isolated muscle strips from the cat fundus and duodenum showed a higher sensitivity to GRP-10 than to NMB. In both segments, BME shifted the GRP-10 and NMB concentration-response curves to the right, while SSocta had no effect. The antagonism of BME was competitive on duodenal but not competitive on fundic muscle. We conclude that the direct myogenic action of GRP-10 and NMB in the esophagus is mediated mainly via NMB-preferring receptors, while GRP-preferring receptors are responsible for the contractile responses to bombesin-like peptides in feline fundus and duodenum. Our data suggest that the GRP receptor population located on fundic muscle might be nonhomogeneous.

Animals↗

PubMed1998

Participation of M1 receptors in NO pathway in cat ileum.

Electrical field stimulation (EFS) elicited two types of responses from longitudinal muscle strips of the distal cat ileum: contraction at switching on the stimulation (in 62% of the strips) and inhibition of the phasic contractions at switching on the stimulation followed by contraction in 38% of the strips. In all strips the muscarinic acetylcholine subtype M1-receptor agonist (4-Hydroxy-2-butynyl)-1-trimethylammonium-m-chlorocarbanilate chloride (McN-A-343) increased the tone and amplitude of the spontaneous contractions. On this background EFS elicited an inhibition of the phasic contractions at switching on the stimulation followed by contraction. Blockade of nitric oxide (NO)-synthase by Nw-nitro-L-arginine (L-NNA) transformed the inhibitory response into contraction and this transformation was partly overcome by L-arginine. The results suggest that presynaptically situated M1 receptors are involved in the NO pathway.

(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethy↗

PubMed1996

Non-adrenergic non-cholinergic neuron stimulation in the cat lower esophageal sphincter.

Both electrical field stimulation and nicotine produced non-adrenergic non-cholinergic (NANC) relaxation of the circular muscle strips from the cat lower esophageal sphincter in the presence of 5 microM guanethidine and 5 microM scopolamine. Low-frequency stimulation (2 Hz, 0.2 ms duration, supramaximal current intensity, 20-s train) provoked a transient relaxation, while at high-frequency stimulation (20 Hz) a slow restoration to the resting tone was observed. Blockade of nitric oxide (NO) synthesis by 1 mM N omega -nitro-L-arginine decreased by 20% the amplitude of the 20 Hz-induced relaxation and changed the pattern of relaxation, making it similar to the sustained relaxation evoked by exogenously applied vasoactive intestinal peptide (VIP). After chymotrypsin (4 U/ml), the pattern of the high-frequency-induced relaxation resembled that of the low-frequency-induced relaxation. Similarly, chymotrypsin changed the shape of nicotine-provoked relaxation, increasing the speed of restoration to the resting tone. We suggest that the fast relaxation elicited in cat lower esophageal sphincter by electrical field stimulation or nicotine is initiated by NO. The slow restoration to the resting tone in the case of high-frequency- or nicotine-induced relaxation seems to be due to the release of VIP or VIP-like peptides. The possibility of participation of another transmitter(s) involved in NANC relaxation should not be excluded.

Animals↗

PubMed1996

Nitric oxide modulates cholinergic neurotransmission in cat duodenum.

1. Longitudinal muscle strips isolated from cat proximal duodenum were characterized by spontaneous phasic contractions. 2. Electrical field stimulation (EFS) (0.5 ms, 1-20 Hz, supramaximal voltage intensity for 40 sec) produced frequency-dependent contractions, and maximal amplitude was achieved at 10 Hz. The EFS-induced contractions were abolished either by atropine (10(-6) M) or by tetrodotoxin (3 x 10(-7) M). 3. The nitric oxide (NO) synthase blocker N infinity-nitro-L-arginine (L-NNA, 10(-4) M) or the inhibitor of the soluble guanylyl cyclase methylene blue (MB, 3 x 10(-5) M) increased the amplitude of the electrically evoked contractions. 4. L-Arginine (10(-3) M) or sodium nitroprusside (SNP, 10(-4) M) significantly decreased the amplitude of the EFS-induced, L-NNA- or MB-potentiated contractions as the effect of SNP was much more pronounced. 5. Neither L-NNA nor MB affected the contraction evoked by exogenous acetylcholine. 6. The L-NNA or MB-induced interruption of the L-arginine-NO pathway potentiated the electrically evoked cholinergic contractions, suggesting the inhibitory role of NO in the cholinergic neurotransmission realized probably at the pre-synaptic level in cat duodenum.

Animals↗

PubMed1996

Effect of substance P and met-enkephalin on cat colonic smooth muscle activity.

1. The effects of substance P (2.5 x 10(-8)M) (SP) and met-enkephalin (10(-7)M) (ME), when administered alone or in combination (SP + ME), on the contractile activity of cat colonic muscle strips were compared. 2. SP evoked powerful contractions of the circular muscle strips (2.30 +/- 0.36 g) (background 0.65 +/- 0.10 g). 3. In the majority of cases, ME significantly increased the background activity (1.88 +/- 0.34 g and 0.70 +/- 0.10 g, respectively). 4. The two substances administered together produced the most pronounced contractile activity (3.86 +/- 0.44 g). 5. The longitudinal muscle strips showed higher spontaneous and evoked contractions. 6. Thus ME contributes to the increase in the effect of SP on colonic contractile activity.

Animals↗

PubMed1994

Participation of nitric oxide in the nicotine-induced relaxation of the cat lower esophageal sphincter.

The participation of nitric oxide in the relaxation of the cat lower esophageal sphincter muscle strip in response to electrical field stimulation or administration of nicotine was studied. The nicotine-induced relaxation was mediated via a neuronal pathway, since it was inhibited by administration of hexamethonium or tetrodotoxin. Inhibition of nitric oxide biosynthesis by N-nitro-L-arginine decreased the relaxation induced by nicotine (50 microM) or field stimulation. With the maximal concentration of N-nitro-L-arginine (1 mM) electrical field stimulation-induced relaxation was abolished, while nicotine-induced relaxation decreased by 70%. L-Arginine (1 mM) partly restored this relaxation. Desensitization of P2x receptors by alpha, beta methylene-adenosine 5-triphosphate (alpha, beta-m-ATP) did not change the relaxation induced by either electrical field stimulation or administration of nicotine. It is therefore suggested that the field stimulation-induced relaxation is mediated by the release of nitric oxide, but in the nicotine-produced relaxation is only partly due to nitric oxide, other factor(s) might be also be involved.

Adenosine Triphosphate↗

PubMed1994

Role of nitric oxide in mediating non-adrenergic non-cholinergic relaxation of the cat ileocecal sphincter.

The participation of nitric oxide (NO) in field stimulation- or nicotine-evoked non-adrenergic non-cholinergic (NANC) relaxation of cat ileocecal sphincter was studied in vitro. During a 30 microM noradrenaline-induced contraction, both the application of electrical field stimulation (2-20 Hz, 0.2 ms, supramaximal current intensity, 10 s duration) and (-)-nicotine (10-500 microM) produced a tetrodotoxin-sensitive relaxation. The maximal relaxation was observed at 10 Hz or 100 microM (-)-nicotine. In 12 out of 19 strips the pretreatment with N omega-nitro-L-arginine (100 microM) decreased the amplitude of the field stimulation-evoked relaxation, while in the remaining strips the relaxation was transformed into a contraction. By increasing the concentration of N omega-nitro-L-arginine up to 1 mM all strips responded to field stimulation with a frequency-dependent tetrodotoxin-resistant contraction. N omega-Nitro-L-arginine (100 microM) completely inhibited the nicotine-induced relaxation. L-Arginine (1 mM) restored the amplitude of both field stimulation- and nicotine-evoked relaxations. These data indicate that NO appears to be involved in both field stimulation- and nicotine-evoked NANC relaxations. Evidence has been obtained for the existence of tetrodotoxin-resistant NANC contraction in cat ileocecal sphincter.

Animals↗

PubMed1994

Some characteristics of the muscularis mucosae of the cat lower esophageal sphincter.

1. The contractile activity of muscularis mucosae strips isolated from cat lower esophageal sphincter (LES) was studied. 2. LES muscularis mucosae strips were characterized by spontaneous phasic contractions. 3. Acetylcholine (ACh) at a threshold concentration of 10(-8) M dose-dependently increased the basal tone and decreased the amplitude of the phasic contractions. Noradrenaline (NA) also increased the basal tone but at a higher threshold concentration (10(-6) M). 4. Nicotine (N) at concentrations of 5 x 10(-5)-10(-4) M induced a relaxation of the LES muscularis mucosae. The N-induced relaxation was tetrodotoxin (TTX) (10(-6) M) sensitive and was insignificantly reduced after guanethidine (5 x 10(-6) M) plus scopolamine (5 x 10(-6) M) or propranolol (10(-6) M). The N-induced relaxation was strongly decreased by the blocker of nitric oxide (NO) synthesis N omega Nitro-L-Arginine (L-NNA) (10(-4) M). The relaxation was restored after addition of L-arginine (10(-3) M). 5. These results suggest the involvement of NO in the N-induced relaxation of the muscularis mucosae.

Acetylcholine↗

PubMed1992

Effect of neurotensin on contractile activity and [3H]acetylcholine release in cat terminal ileum during different postnatal periods.

The effect of neurotensin (NT) on the contractile activity of circular and longitudinal strips from the terminal ileum of 15-, 30-, 60-day-old and adult cats as well as on the resting and electrically-evoked release of [3H]acetylcholine (ACh) was studied. Radioactivity was measured by liquid scintillation spectrometry and the effect of NT was evaluated by the S2/S1 ratio. In the circular muscle strips NT (1-100 nM) inhibited spontaneous contractions in all age groups. In the longitudinal strips the effect of NT was concentration- and age-dependent. NT at a concentration of 1 nM had no effect on the spontaneous activity in 15-day-old cats, but in the other age groups in 70-80% of the cats it inhibited spontaneous contractions. The response to 10 and 100 nM NT was either biphasic (relaxation followed by contraction) or inhibitory: in 15-day-old cats the response was biphasic only and with increasing age the percentage of strips responding with inhibition of the contractions increased. Neither substances affecting adrenergic and cholinergic transmission nor TTX changed the inhibitory response to NT. The contractile component of the biphasic response was TTX-resistant in all age groups and was significantly decreased by scopolamine in 60-day-old and adult cats. NT increased both resting and electrically-evoked release of [3H]ACh which was not changed by TTX. In the presence of the peptide the S2/S1 ratio increased as NT-induced [3H]ACh release in the strips of adult cats was higher than that in young cats.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed1992

Effect of cromakalim on the smooth muscle of the cat gastric antrum.

The effect of the K(+)-channel opener cromakalim (BRL 34915) on the electrical and contractile activity of the smooth muscle of the cat gastric antrum has been studied. Cromakalim induced a concentration-dependent inhibition of the contractions and shortening of the sustained partial repolarization phase of the plateau action potential. High concentrations of cromakalim produced hyperpolarization and shortening of the repolarization and depolarization phases of the plateau action potential. The K(+)-channel blockers 4-aminopyridine (10(-2) M) and tetraethylammonium (10(-2) M) decreased the effect of cromakalim on the phasic contractions, while glibenclamide (5 x 10(-5) M) completely abolished it. We suggested that the inhibitory effect of cromakalim on the electrical and contractile activity of the gastric antrum smooth muscle is due to the cromakalim-induced increase of the outward K(+)-current through glibenclamide-dependent K(+)-channels.

Action Potentials↗

PubMed1991

The dual effect of BAY K 8644 on excitation-contraction coupling in gastric smooth muscle.

1. BAY K 8644 at concentrations of 10(-10)-10(-6) M had a stimulant effect on the spontaneous electrical and contractile activity of smooth muscle preparations from cat and guinea pig stomach. 2. Nifedipine (10(-6) M) antagonized the BAY K 8644-induced spike potentials and the related phasic contractions. 3. Neither the excitatory nor the inhibitory effect of BAY K 8644 was significantly influenced by atropine (10(-7) M), phentolamine (10(-7) M), propranolol (10(-7) M) or TTX (10(-6) M). 4. TEA (10(-3) M) abolished the inhibitory effect of BAY K 8644 on the spike generation and increased the amplitude of the phasic contractions.

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

PubMed1991

Prejunctional nicotinic receptors involved in facilitation of stimulation-evoked noradrenaline release from the vas deferens of the guinea-pig.

In guinea-pig prostatic vas deferens loaded with [3H]-noradrenaline ([3H]-NA), nicotinic receptor agonists, nicotine and dimethylphenylpiperazinium (DMPP) enhanced the resting and facilitated the stimulation-evoked release of [3H]-NA in a concentration-dependent fashion. The effect of nicotine on both contraction of vas deferens and release of NA in response to field stimulation was stereospecific in favour of the naturally occurring (-)-enantiomer. Prolonged (15 min) exposure to (-)-nicotine resulted in a cessation of the facilitatory effect on NA release and on responses of the vas deferens to field stimulation. 2 The rank order of agonist potency in facilitating NA release was DMPP = (-)-nicotine greater than (+)-nicotine. Cytisine had no agonistic activity. The dissociation constants (KD) of antagonists were 9.3 +/- 0.6 and 31.4 +/- 2.4 microM for (+)-tubocurarine and hexamethonium, respectively, when (-)-nicotine was used as agonist. alpha-Bungarotoxin had no antagonistic activity. These findings suggest that nicotinic receptors located on noradrenergic axon terminals are different from those located postsynaptically in striated muscle or ganglia but seem similar to those present on cholinergic axon terminals at the neuromuscular junction. 3. Cotinine, the breakdown product of nicotine failed to have any agonistic activity indicating that nicotine itself is responsible for the effects observed on axon terminals. 4 Stimulation of presynaptic muscarinic receptors by oxotremorine prevented the nicotine-induced facilitation of [3H]-NA release, indicating the presence of both inhibitory muscarinic and facilitatory nicotinic receptors on noradrenergic axon terminals.

Animals↗

PubMed1991

[Gastrointestinal sphincters--pharmacologic viewpoints].

Bearing in mind the specificity of the functions of the gastrointestinal sphincters (GIS), we studied the responses of the lower esophageal sphincter (LES), the pyloric sphincter (PS), the ileocecal sphincter (ICS) and the internal anal sphincter (IAS) to noradrenaline (NA), acetylcholine (ACh), PGE1, PGF2 alpha and the peptide bombesin (B). The electrical and contractile activities as well as the response to field electrical stimulation (FES) were recorded. All sphincters except for PS responded to NA with depolarization and contractions. ACh at concentrations higher than 5 x 10(-6)M elicited a biphasic response from LES: depolarization followed by hyperpolarization and respectively contractions and relaxation. At concentrations higher than 10(-6)M ACh produced hyperpolarization and relaxation in IAS. Data were obtained about the modulating role of presynaptic N-cholinoreceptors in the release of a non-adrenergic, non-cholinergic (NANC) inhibitory neurotransmitter leading to hyperpolarization and relaxation in LES and IAS under the effect of exogenous ACh. PGE1 and PGF2 alpha increased the tone and decreased the FES-induced relaxation in LES. In PS PGE1 evoked relaxation and completely inhibited the response to FES. The pharmacological analysis showed that PGs modulated not only the adrenergic and cholinergic but also the NANC neurotransmission. Evidence is presented concerning the role of bombesin in the adrenergic, cholinergic, and NANC neurotransmission in LES.

Acetylcholine↗

PubMed1990

Inhibitory effect of hypoxic condition on acetylcholine release is partly due to the effect of adenosine released from the tissue.

Isolated longitudinal muscle strip with Auerbach's plexus attached was used to study the stimulation-evoked release of 3H-acetylcholine (3H-ACh) under normoxic and hypoxic conditions. Hypoxia reduced the release of ACh. Theophylline, a purinoceptor P1 antagonist and vinpocetine, an antiischemic compound partly reversed the effect of hypoxia. Unlike theophylline, the effect of vinpocetine was not mediated via adenosine action, since it failed to affect the presynaptic action of adenosine, and the effect of theophylline and vinpocetine was additive. When they were added together the effect of hypoxia was almost completely antagonized. Dipyridamole, an adenosine uptake inhibitor, potentiated the effect of hypoxia and the presynaptic inhibitory action of adenosine on ACh release. Evidence was obtained that the effect of hypoxia is at least partly due to adenosine formed from purine nucleotides.

Acetylcholine↗

PubMed1990

Antiexudative and capillaritonic effects of procyanidines isolated from grape seeds (V. Vinifera).

A purified and enriched fraction, containing procyanidines, was isolated from grape seeds of Bulgarian sorts of Vitis Vinifera. The effects of procyanidines on the local oedema, produced by subplantar injection of carrageenin and dextran in the hind rat paw, were studied. We also tested their effect on the capillary permeability using intravenous injection of Evans blue and local irritation by xylene. Procyanidines at a dose of 2 mg/kg applied orally three times daily for 6 days inhibited the carrageenin-induced hind paw oedema. On the same schedule of administration these compounds inhibited the dextran-induced oedema 4 hours after the development of the process. Procyanidines stabilized the capillary wall and prevented the increase of capillary permeability caused by local cutaneous application of xylene.

Animals↗