Biomedical subjects

E Atanassova

Publications and source records attributed to E Atanassova.

At least 19 recordsLinked to original sources

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↗

PubMed1995

Non-invasive electrogastrography. Part 1: Correlation between the gastric electrical activity in dogs with implanted and cutaneous electrodes.

Experiments were made on dogs with bipolar silver ball-shaped electrodes chronically implanted on the muscle wall of the stomach. The electrical activity of the gastric muscle wall (electrogastromyogram-EGMG) was characterized by slow potential changes during the quiescent period of the migrating myoelectric complex (MMC) and bursts of spike potentials during the activity period of MMC. Cutaneous (surface) electrodes were placed on the abdominal wall. Waves with a rhythm of 4.5-5 cpm were led off by the cutaneous electrodes (electrogastrogram-EGG), simultaneously with the EGMg. The bursts of spike potentials with the slow gastric potentials in the EGMG corresponded to an increase of the amplitude of the waves in the EGG. Good correlation was found between the number and frequency of spike potentials in a group and the wave amplitude in the EGG. EGG recorded on an electrogastrograph designed by us was characterized by low-amplitude waves corresponding to the slow waves during the period of quiescence of MMC and high-amplitude waves corresponding to the bursts of spike potentials during the activity period of MMC. Therefore it is possible to determine the MMC of the stomach by the changes in the amplitude of the waves in the EGG.

Action Potentials↗

PubMed1995

Non-invasive electrogastrography. Part 2. Human electrogastrogram.

The electrical activity of human stomach muscle wall-electrogastrogram (EGG), was led off by surface (cutaneous) electrodes placed on the abdominal wall and recorded on an electrogastrograph. A method for complete elimination of the cardiac artefact was elaborated and successfully implemented. It consists of a preliminary elimination of the QRS complex, based on its higher amplitude and slope. The eliminated intervals were replaced by linear segments. A subsequent low-pass filtering allowed to obtain a high quality EGG signal. The electrical activity of the stomach of healthy volunteers was characterized by waves with a frequency of 3.35 +/- 0.09 cpm during the quiescent periods and 2.99 +/- 0.14 cpm during the activity periods of the migrating myoelectrical complex (MMC). Bearing in mind the correlation between the bursts of spike potentials with the slow waves in the dog EGMG and the high-amplitude waves, characterizing the periods of activity in the dog EGG, we can better differentiate the periods of quiescence and activity by the amplitude of the waves. The wave amplitude during periods of quiescence was 81.13 +/- 20.61 microV, significantly different from the wave amplitude during periods of activity being 164.74 +/- 43.34 microV (n = 7). Thus with this method in visual inspection it is possible to identify MMC of the human stomach by the changes in the amplitude of the waves in the EGG.

Action Potentials↗

PubMed1995

Possibilities of the non-invasive electrogastrography.

A non-invasive method for recording the electrical activity of the gastric muscle wall is presented. Electrogastrograms (EGG) with cutaneous electrodes on the abdominal wall were recorded using an original electrogastrograph. High-quality records without cardiac artifacts allowed for identification of waves belonging to the quiescent or activity period of the migrating myoelectric complex (MMC). The amplitude of the waves of the activity period of MMC were almost twice higher than that of the waves of the quiescent period. The wave amplitude immediately after feeding increased two times and a half compared to that during fasting. The high-amplitude waves in the activity periods of MMC and after feeding in the electrogastromyograms (EGMG) of dogs corresponded to bursts of spike potentials with slow potentials, i.e. to intense gastric muscle wall contractions. The method could contribute to the diagnosis of gastric motility disturbances in clinical practice.

Action Potentials↗

PubMed1993

Effects of cholecystokinin octapeptide and somatostatin on the motility and release of [3H]acetylcholine in canine colon.

1. The longitudinal and circular muscle layers of canine colon showed a different pattern of mechanical activity: regular rhythmic phasic contractions in the circular strips and irregular rhythmic prolonged contractions in the longitudinal strips. 2. The spontaneous motility of both layers was suppressed by atropine (1 microM) or hexamethonium (1 microM), suggesting the involvement of ACh. 3. Somatostatin (1 nM-1 microM) decreased, while CCK8 (1-10 nM) increased the spontaneous and electrically-induced contractions of the colonic muscles, the circular layer being more sensitive as compared to the longitudinal layer. 4. CCK8 enhanced both resting and electrically-induced [3H]ACh release, while SOM inhibited the electrically-stimulated [3H]ACh release.

Acetylcholine↗

PubMed1993

Changes in the electrical activity of the gastric remnant after Billroth II gastrectomy in dogs.

Chronic experiments were performed on dogs with Biller II gastrectomy followed by Roux-Y gastrojejunostomy. Gastric mucosa valve was made in the region of the gastrointestinal anastomosis in order to prevent the rapid gastric evacuation. Electrical activity of the gastric remnant, duodenum and jejunum was led off by six bipolar, silver, ball-shaped electrodes, implanted subserously on the muscle wall. Continuous bursting of groups of spike potentials with the slow gastric potentials in the usual rhythm (4.5-5 cpm) occurred during the 1st month after surgery. However, at the end of the 2nd month after surgery there were periods of tachygastria. The frequency of the gastric potentials was lower (7.52 +/- 1.37 cpm, n = 26) or higher (20.40 +/- 0.68 cpm, n = 30) compared to that of the jejunal slow waves (14.11 +/- 0.18 cpm, n = 50), i.e., it was different from the frequency of the jejunal slow waves.

Animals↗

PubMed1991

Character of the excitatory neurotransmission in dog terminal ileum.

In vitro experiments were performed on smooth muscle strips cut out longitudinally or circularly from the terminal ileum at about 5 cm from sphincter ileo-colocum of 3-4-month old and adult dogs. Studies were made on the postsynaptic responses of single smooth-muscle cells to transmural electrical stimulation of strips placed in sucrose gap, as well as on the contraction changes in response to field electrical stimulation of strips placed in organ bath. Field electrical stimulation elicited mainly excitatory responses of the muscle strips. Using cholino- and adrenoreceptor-antagonists and serotonergic receptor-blockers, we found that the majority of responses were cholinergic and a small part of them were alpha-adrenergic. Excitatory serotonergic responses were also obtained. The nerve nature of the responses was proved by tetrodotoxin. Single smooth-muscle cells gave predominantly excitatory postsynaptic responses to transmural stimulation of the smooth muscle strips. The pattern of both postsynaptic and contractile responses changed in the presence of the antagonists used. The present results suggest the predominance of cholinergic transmission in the contractile responses of the terminal ileum.

Animals↗

PubMed1991

Changes in the responsiveness of the colonic smooth muscle to carbachol in Hirschsprung's disease.

In vitro experiments were performed on smooth-muscle strips cut out in longitudinal and circular direction from the colon of Hirschsprung's patients who underwent an operation and from patients operated on for tumors of the sigmoid colon and rectum, serving as controls. The changes in the contractile activity of the smooth-muscle strips after carbachol applied cumulatively were examined and dose-response curves were plotted. The EC50 values for the circular strips from the aganglionic part of the colon were 6 x 10(-7) M in Hirschsprung's patients and 3.7 x 10(-8) M in control patients: the pD2 values were 6.23 and 7.43, respectively. This showed that the affinity of cholinoreceptors in the aganglionic part of the colon for carbachol was 16 times lower in Hirschsprung's patients as compared to control patients. The EC50 values for longitudinal strips from the ganglionic part of the colon were 2.6 x 10(-7) M in Hirschsprung's patients and 4 x 10(-8) M in control patients; pD2 values were 6.6 and 7.4, respectively. The affinity of cholinoreceptors in the smooth muscle of the ganglionic part of the colon for carbachol was also decreased (nearly 6.5 times) in Hirschsprung's patients as compared to controls.

Atropine↗

PubMed1991

Relationship between the spike activities of the small and large intestines.

Experiments were performed using chronically implanted electrodes on the dog smooth muscle wall of the stomach and of the small and large intestines. Electrical activity of the muscle wall was recorded before and after feeding. When reaching the terminal ileum the active part of the migrating myoelectrical complex (MMC) continuously induced bursts of spike potentials superimposed on the slow waves. This electrical activity spread to the ascending colon. We also showed the existence of a spike activity on the terminal ileum independent of the MMC (appearing during the phase 1) and propagating to the colon. A relationship between the spike activities of the small and large intestines was also present after feeding. Beside the well-known gastro-colic reflex, we observed an increase in the spike activity of the terminal ileum and ascending colon between the 4th-5th hours after feeding. This probably corresponds to the arrival of the first portions of contents, evacuated from the arrival of the first portions of contents, evacuated from the stomach, and of the last portions of small intestinal contents. In conclusion, there is a relationship between the spike activities of the small and large intestines in starving animals and after feeding, and the terminal ileum plays a substantial role in this relationship.

Action Potentials↗

PubMed1990

Acetylcholine release in two parts of the canine ileum.

1. Electrically-induced contractions and acetylcholine (Ach) release in two parts of the ileum: 5 and 25 cm proximal to the ileo-colic sphincter (ICS) were compared. 2. The amplitude of electrically- and Ach-induced contractions of the ileum 5 cm proximal to the ICS (terminal ileum) was much higher than the amplitude of the contractions of the ileum 25 cm proximal to the ICS. 3. The amount of Ach released in the ileum 25 cm proximal to the ICS accounted for 58% of the amount of Ach released in the terminal ileum, which was taken to be 100%.

Acetylcholine↗

PubMed1989

The role of the pelvic nerves in the realization of the reservoir function of the colon.

In situ experiments were made on a group of dogs and in vivo experiments on another group of dogs with implanted electrodes for recording the electrical activity of the colonic muscle wall. A bipolar platinum electrode implanted in the pelvic nerve entering into the distal area of descending colon was used for electrical stimulation of the nerve (1 ms impulse duration, frequency of 2, 8, 10 and 15 Hz and amplitude of 10, 15 or 20 V). Electrical stimulation of the pelvic nerve with a frequency of 2 Hz resulted in inhibition of the spike activity. However, groups of spike potential burst in the distal part of the descending colon in response to electrical stimulation with frequencies of 8, 10 or 15 Hz. Repeated stimulation caused spreading of the spike activity of the descending colon in oral direction until the transverse colon. These antiperistaltic waves probably prevented the propulsion of the content of the descending colon. Thus, in addition to the inhibitory effect exercised by the sympathetic and noncholinergic nonadrenergic inhibitory part of the intrinsic nervous system, the reservoir function of the colon is influenced by these orally spreading waves of spike activity (antiperistaltic waves), which are caused by impulses along the pelvic nerves.

Animals↗

PubMed1987

On the mechanism of the smooth-muscle action of rosanol.

In vivo and in vitro experiments were performed to clarify some aspects of the mechanism of the smooth-muscle action of rosanol prepared from rose oil. On dogs (in vivo) and on isolated segments from guinea-pig ileum (in vitro) rosanol at high doses exerted a slight inhibitory effect on the activated gastrointestinal motility. The cholinolytic rosanol action proved in in vitro experiments, was found to play an essential role in the mechanism of its gastrointestinal motility-inhibiting effect. The present studies showed a pronounced antagonistic effect of rosanol on the KCl-increased Ca2+ level in rabbit aorta. It might be suggested that this effect of rosanol is also involved in the inhibitory action of rosanol on the activated gastrointestinal motility.

Animals↗

PubMed1986

Changes in the reactivity of the intrinsic nervous system of the stomach to hexamethonium after transthoracic vagotomy.

Experiments were carried out on seven breedless dogs with chronically implanted electrodes in the stomach. The effect of hexamethonium (in doses of 0.2, 0.3, 0.5, 1, 2, 3, 5, 7 and 10 mg/kg, i. v.) on the migrating myoelectrical complex (MMC) was studied before and after transthoracic vagotomy. Injected on the background of the first MMC phase, hexamethonium in doses of up to 2 mg/kg induces the appearance of spike potentials (SP). Applied on the background of spike activity, hexamethonium induces the appearance of spike activity of the type of the 3rd MMC phase. In a dose exceeding 2 mg/kg, introduced during SP activity, hexamethonium interrupts for different periods of time the SP generation and shortens the duration of the active MMC phases. On the background of increased spike activity characteristic of the stomach after vagotomy, 3 mg/kg hexamethonium have almost no effect on the electrical activity, whereas 10 mg/kg only reduce the percentage of slow waves accompanied by SP. It is probably that after vagotomy the excitability of the intrinsic nerve cells is increased, therefore even the high doses of the ganglionic blocker hexamethonium cannot inhibit entirely the active phases of MMC.

Animals↗

PubMed1984

Spike activity of the muscle wall of the stomach remnant after gastric resection.

Chronic experiments have been carried out on dogs with implanted bipolar silver ball-shaped electrodes on the muscle wall of the stomach remnant after gastric resection. It has been found that in the first group of animals with subtotal gastrectomy (the frequency of the slow potentials during late periods after the resection increases and reaches the frequency of the corpus and antrum) the spike activity is represented by small groups of low-amplitude and low-frequency spike potentials. In the second group of animals for which the resection line passes at a distance of 1 to 1.5 cm distally from the boundary between the fundus and the corpus of the stomach (the frequency of the slow potentials increases to about 4 cpm even at the end of the first postoperational week), large groups of relatively high-amplitude and high-frequency spike potentials burst with the rhythmic slow potentials. The faster and better adaptation of the stomach remnant after sparse resection (2nd group of animals) is considered to be due to the existence of part of the pacemaker area in the stomach remnant. The spike activity characterizing the myoelectric complex is a prerequisite for the realization of the evacuation function by the stomach remnant.

Action Potentials↗

PubMed1984

Electrical activity of the stomach: nervous control.

The role of the extramural vagus nerves in the modulation of gastric electrical activity and the myoelectrical complex (MEC) was studied by electrical stimulation of the nerve of Latarjet. As a consequence of the interruption of vagal impulses for five months by bilateral transthoracic vagotomy, the intramural nervous system began to perform as an organiser and modulator of the disorganised gastric electrical activity. The modulating role of the intramural nervous system was also demonstrated by stimulating the transmural electrical system, using parameters such as spike-firing and duration of stimulation of the MEC, and by blocking the adrenergic receptors.

Action Potentials↗

PubMed1982

On the character of the electrical activity of the stomach, pyloric sphincter and duodenum of cats.

In cats with chronically implanted electrodes in the muscle wall of the gastro-intestinal tract, the electrical activity of the stomach (S) pyloric sphincter (PS) and duodenum (D) is characterized by cycles consisting of two phases: active--whereby 2 to 3 slow potential changes (SPC) are accompanied by spike potentials (SP) and a pause during which for 60-90 s only SPC are recorded. After bilateral transthoracic vagotomy there is a disruption of the cyclic character of the electrical activity in the investigated regions of the gastro-intestinal tract--SP from S and PS are recorded with each SPC. The active phase of the cycle from D is strongly prolonged at the expense of the shorter pause. This lasts for 1-2 days, after which there is a tendency towards shaping the cycles characteristic of the electrical activity of S, PS and D of cats. The pauses, however remain relatively short and the number of SP in the group is much greater. Gradually during the second month the character of the electrical activity of S, PS, and D approaches that prior to the vagotomy, but even until the 6th month after vagotomy the number of SP in the group is greater and the active phase of the cycle is longer. On the background of antagonists of the adrenoreceptors (propranolol--2 mg/kg and dihydroergotamine--300 micrograms/kg), the cyclic character of the electrical activity of S, PS and D is disturbed. The relatively rapid restoration of the cyclic character of cat S, PS and D after vagotomy is assumed to be the result of the organizing role of the intrinsic nervous system. The disturbance of the cyclic character after adrenoblockers demonstrates the significance of the balance between the cholinergic and adrenergic parts of the intrinsic nervous system for the realization of the cyclic character of the electrical activity of S, PS and D of cats.

Animals↗

PubMed1982

Character of the nerve transmission in different stomach regions.

A microelectrode study is performed of the postsynaptic potentials of single smooth-muscle cells from various regions of cat stomach. The smooth-muscle cells from the region of the fundus, the corpus along the small curvature, as well as from the middle region of the anterior wall, produce more frequently inhibitory responses to transmural electrical stimulation, while the cells of the cardia, of the corpus along the big curvature and the antrum respond predominantly by depolarization and contraction of the muscle strip (excitatory responses). Administration of atropine in doses of 10(-6) M blocks the excitatory postsynaptic potentials, which suggests that the majority of them are cholinergic. By adding adrenergic antagonists in a dose of 10(-6) M it is demonstrated that a part of the inhibitory responses are produced by nonadrenergic inhibitory nerve fibres. The differences in the nerve transmission of different stomach regions may be associated with the possibilities of exercising the reservoir or evacuative function of these regions.

Animals↗

PubMed1982

Histochemical study of the myenteric plexus following gastric resection on dogs.

Enzyme histochemical methods were used to follow up to changes within the myenteric plexus from 1 week to 7 months following subtotal Billroth I gastric resection in dogs. Different regions of the resected stomach were examined. The changes affected the neurons and the neuropil of the myenteric ganglia, the connecting strands and the nerve bundles and fibers within the muscle layers. The changes in size, from and enzyme activity of some myenteric neurons correspond to those observed during axon regeneration. The 2nd week showed a significant reduction of the nerve cell number in most of the examined regions of the resected stomach. Along with, the amitotic forms of cell division and immature nerve cells became more numerous. The enzyme activity of the latter increased with the time elapsed after resection, 7 months afterwards, the size of the myenteric ganglia in the resected stomach did not differ from those in the control dogs. There were some hypertrophic nerve cells with higher enzyme activity. Some changes presume the formation of new intramural ganglia. The changes in the myenteric neurons were accompanied by reactive changes in the non-neuronal elements. Hyperinnervation was observed in the gastric muscles.

Animals↗