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Biomedical subjects

V Petkov

Publications and source records attributed to V Petkov.

At least 55 records · Page 3Linked to original sources
PubMed1983

Electrophysiological effects of propranolol and carbachol locally injected into nucleus raphe dorsalis in cats.

The effect of propranolol and carbachol injected directly into nucleus raphe dorsalis (RD) on the evoked potentials, their recovery cycles and on the spontaneous EEG activity recorded in the RD and the visual and somatosensory cortical regions was investigated. It was found that the changes in these electrophysiological parameters induced by propranolol and carbachol were similar and showed an increase in the excitability level in both the RD and the neocortex, mainly in the somatosensory cortex. The activating effect of carbachol was much more pronounced as compared with that of propranolol. The results are discussed in relation to the possible interactions between various neurotransmitter systems within the RD as well as to the data about the presumed role of this nucleus in some behavioral and/or electrophysiological manifestations. The findings suggest that raphe dorsalis participates in the regulation of the cortical excitability and apparently represents a system which modulates the transMission and integration of sensory information.

Animals↗
PubMed1982

Effects of some benzodiazepines on the acetylcholine release in the anterior horn of the lateral cerebral ventricle of the cat.

Studies were made of the effects of the benzodiazepines clonazepam (Cz), flunitrazepam (Fz) and Diazepam (Dz) on the spontaneous release of acetylcholine (ACh) in the anterior horn of the lateral cerebral ventricle of cats superficially anaesthetized with urethane. The amount of released ACh was determined in 15-min samples by a bioassay on a segment from isolated guinea-pig ileum. It was found that benzodiazepines applied i.p. in doses of: 5 mg/kg (Dz), 10 mg/kg (Cz) and 0.5 mg/kg (Fz) decreased the ACh release in the effluent flowing out through the cannulated aqueduct. If the released ACh in the sample taken immediately before the administration of benzodiazepine was considered to be 100 per cent its amount in the samples after injection of benzodiazepine changed as follows (in per cent): for Dz - 34.2, 70.2, 65.7, 40; for Cz - 46.3, 33.1, 26, 50.6; and for Fz - 46.1, 46.1, 28.2, 39.4. It is assumed that the benzodiazepine-induced reduced release of ACh from the caudate nucleus--a main structure participating in the building up of the anterior horn of the lateral cerebral ventricle--is a manifestation of inhibition of ACh turnover which might be due to inhibition of the activity of the serotoninergic neurons in the raphe nuclei. The decreased ACh release might also be due to inhibition by benzodiazepines of the Ca2+-dependent release of ACh.

Acetylcholine↗
PubMed1982

Effects of glaucine and some glaucine derivatives and of their combination with L-DOPA on the brain level of biogenic monoamines.

Glaucine and two of its structural analogues exerted an inhibitory effect on phosphodiesterase activity in different tissue homogenates. In experiments on rats glaucine applied intraperitoneally significantly increased the brain level of dopamine (DA) and did not change the content of noradrenaline and serotonin (5-HT). The combined application of L-DOPA and glaucine or glaucine derivatives produced a higher increase in brain DA than the increase which would be expected by simple summation of the effects of L-DOPA and glaucine and of the glaucine derivatives respectively. At the same time L-DOPA and glaucine, applied together, caused a slighter decrease of brain 5-HT than the decrease produced by the same dose of L-DOPA when the latter was applied alone. It is suggested that the higher increase of brain DA produced by the combination of L-DOPA and the phosphodiesterase inhibitor glaucine or its structural analogues is mainly due to the increased cAMP level.

Animals↗
PubMed1981

Effect of chronic para-chlorophenylalanine treatment on convulsive-seizure reactions.

The effect of chronic para-chlorphenylalanine (PCPA) treatment was investigated in two different seizure models: the pentylenetetrazole (PTX) seizure model in rats and the kindled seizures from rabbit amygdala. Chronic PCPA treatment (21 days) in male albino rats caused a progressive decrease in the 5-hydroxytryptamine (5-HT) brain level between the 1st and the 7th day of PCPA administration. Then the 5-HT level remained low until the end of the experiment. On the background of the low 5-HT level there occurred changes in PTZ convulsive reactions: after the 3rd day of PCPA treatment the convulsive-seizure reactivity was significantly increased and after the 7th, 14th and 21st day the increased seizure reactivity performed only as a tendency, though the 5-HT level was still low. Chronic PCPA treatment (16 days) of rabbits delayed the development of the behavioural kindled seizures. This treatment also reduced the duration of bioelectrical seizures until the 8th day of treatment, especially in the motor cortex. The observed different effect of the chronic PCPA treatment in both seizure models: pentylenetetrazole in rats and kindling in rabbits might be explained by essential differences in the origin and mechanisms of development of the two seizure models.

Amygdala↗
PubMed1981

Role of calcium ions and of the cholinergic system in the contractile effects of prostaglandin F2 alpha on intestinal smooth muscle (experiments on cat jejunum).

The cumulative contractile effect of prostaglandin F2 alpha (PGF2 alpha) on isolated longitudinal muscle of cat jejunum has been studied at different Ca-content in the nutrient solution (2.5, 1.0 and 6.25 mM) and on the background of pretreatment with physostigmine and atropin. PGF2 alpha contracts in a dose-dependent degree the longitudinal muscle of the jejunum. The maximum contractile effect of PGF2 alpha (1 x 10(-7)M) increases upon reducing the extracellular calcium (1.0 mM) and decreases when the Ca-concentration is increased to 6.25mM. Similar changes in the PGF2 alpha effect for the Ca-concentration used have also been observed after pretreatment of the preparations with physostigmine (1 x 10(-8)M). The contractile effect of PGF2 alpha considerably decreases on the background of atropin action (1 x 10(-8)M). The inhibitory action of atropin on the PGF2 alpha-induced contraction decreases upon increasing the Ca-concentration in the nutrient solution. The results suggest participation of the cholinergic system in the realization of the PGF2 alpha effect. The possibility of modulating this effect by the calcium regulatory mechanisms of the muscle is discussed.

Animals↗
PubMed1981

[Effect of the psychostimulants caffeine and methylphenidate on the efficiency of physical activity in rats exposed to ionizing radiation].

The authors carried out studies on 267 male rats and examined the effect of ionizing irradation (single irradation with 737 roentgens) on the duration of swimming and on the alteration of this effect by psychic stimulators caffeine and methylphenidate, administered in overthreshold doses (30 and 50 mg/kg of body weight for caffeine and 5 and 10 mg/kg of body weight for methylphenidate). On the 7th day after irradiation there was statistically significant shortening of the duration of swimming in the control animals. The mentioned doses (statistically significant for the larger dose) were used in nonirradiated animals and the two psychic stimulators also shortened the duration of swimming in comparison with the control nonirradiated animals. This effect could be explained by hyperexcitatory action of these doses of caffeine and methylphenidate. As a result of this, desoptimization of the cerebral activity occurred and as a consequence of which was the diminution of the efficiency of the physical activity. Together with this they observed that both psychic stimulators partially counteracted the shortening of the duration of swimming of rats, caused by ionizing irradiation itself. This effect, especially for caffeine, could be explained by the induced of the ionizing irradiation increase in the sensitivity of cerebral phosphodiesterase of rats to its inhibitor caffeine as a result of which under these conditions the effect of caffeine on the level of cerebral cyclic AMP was reinforced. The cyclic AMP is presumed to have some protective effect against ionizing irradiation.

Animals↗
PubMed1981

The effect of new local anaesthetics on tracheal and anococcygeal smooth muscle.

The effects of pentacaine and heptacaine were compared with that of procaine on the isolated tracheal smooth muscle of guinea-pigs and anococcygeal muscle of rats. Pentacaine increased the initial tone of the tracheal smooth muscle. In higher concentration however pentacaine and heptacaine induced smooth muscle relaxation. Pentacaine diminished the action of histamine on the tracheal smooth muscle and both pentacaine and heptacaine depressed the effects of noradrenaline and acetylcholine on anococcygeal muscle.

Anal Canal↗
PubMed1980

In vitro inhibition of cyclic 3' 5',-AMP-phosphodiesterase by a group of structural analogues of glaucine.

Both glaucine and six of its structural analogues applied in increasing concentrations produced a concentration-dependent inhibiton of cyclic 3' 5'-AMP-phosphodiesterase in homogenates from different organs of guinea-pigs and rats. At one and the same concentration of the compound tested the percentage of inhibition varied within wide ranges depending on the compound used, as well as on the organ and on the Km of phosphodiesterase. The changes in the chemical structure of glaucine and the changes in the inhibitory effects on phosphodiesterase activity of tissue homogenates were compared. Some of the compounds applied in appropriate concentrations showed a twice higher inhibitory activity than glaucine. This finding is of particular importance having the mind the much lower toxicity of these compounds compared with glaucine. Essential differences in the dynamics of the concentration-dependent phosphodiesterase inhibition between the compounds were established. The observed peculiarities of the inhibitory effects of the compounds tested favour the concept of the multiple nature of phosphodiesterase. The data from the pharmacological investigation on glaucine and its semisynthetic analogues led us to believe that the effect of 2 compound on phosphodiesterase activity of homogenates from intestinal smooth muscles does not justify any definitive conclusions about the character of its effect on the smooth-muscle activity.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1980

On the interaction of histamine with the tryptaminergic smooth-muscle receptors.

The effect of histamine (1 x 10(-8) to 1 x 10(-3) M) on the contractile effects of 5-hydroxytryptamine (1 x 10(-10) to 1 x 10(-3) M) has been studied in experiments on isolated smooth-muscle preparations (rabbit duodenum and guinea-pig trachea). Applied in lower concentrations in both smooth-muscle preparations, histamine does not influence essentially or slightly lowers the contractions induced by the low concentrations of 5-hydroxytryptamine (5-HT). At the same time the contractile effects of the high 5-HT concentrations are reduced by about 15-30 per cent. Increasing the histamine concentration in the organ bath reveals a potentiation of the contractile responses caused by the low 5-HT concentrations by about 10-25 per cent. The contractile effects of the high 5-HT concentrations are reduced by 10-30 per cent on the background of the high histamine concentrations in advance. The results obtained show that histamine influences the 5-HT-induced contractions most probably through allosteric interaction with the tryptaminergic receptors in the smooth-muscle organs studied.

Animals↗
PubMed1979

Plants and hypotensive, antiatheromatous and coronarodilatating action.

However great the success in the therapy of hypertension, atherosclerosis and ischemic heart disease has been gained today by recent efficient drugs, the definite healing of patients is not yet attained. The late discovery of reserpine, such an efficient drug of plant origin against hypertension, convinced so far reluctant scientists to consider the chemical compounds of the plant world. With respect to this traditional medical knowledge, it seems necessary to define more accurately the specificity of these healings-sometimes recommended unspecifically for a whole branch of medicine. This experimental verification should not use inconsiderately the present-day classification of diseases; there should be an awareness that conventional experimental methods in pharmacology are often unsuitable for revealing the real biological activity of one or another medicinal plant. The interest in the millennial empirical field of health care is acknowledged by the World Health Organization which promotes research and development of traditional medicine, along with investigations into its psychosocial and ethnographic aspects. These studies cover a number of plants growing in Bulgaria that have a healing effect in hypertension, atherosclerosis and ischemic heart disease according to the data of traditional medicine. Using screening methods, extracts and chemically pure substances were investigated; extraction was done with solvents such as water, ether, chloroform, dichloretan, ethanol, methanol, and acetone. Most of the experiments were carried out on anesthetized cats, rabbits and dogs. The substances tested were applied mainly intravenously, and in some experiments orally. Chronic experiments were also carried out on wakeful dogs with induced hypertension, on animals fed on an atherogenic diet, and on animals with induced arrhythmia and coronary spasm. Data are presented of clinical examination of some plants or of active substances isolated from them. Major results of these studies are presented for the following plants: Garlic, Geranium; Hellebore; Mistletoe; Olive; Valerian; Hawthorn; Pseucedanum arenarium; Periwinkle; Fumitory. For another 50 plants growing in Bulgaria and in other countries the author presents his and other investigators' experimental and clinical data about hypotensive, antiatheromatous and coronarodilatating action.

Animals↗
PubMed1979

Effect of centrophenoxine on acetylcholine release in perfused cerebral ventricles of cats under dynamic electrophysiological control.

The effects of centrophenoxine on the release of acetylcholine and on the changes in the bioelectrical activity are determined in experiments on non-anaesthesized cats subjected to perfusion of the anterior horn of the lateral cerebral ventricle and simultaneous recording of the bioelectrical activity of cortical and subcortical structures. Centrophenoxine is tested in doses of 25, 50 and 100 mg/kg intravenously. Most characteristic changes are found to occur after the dose of 50 mg/kg, when centrophenoxine markedly increases the amount of the released acetylcholine and changes the bioelectrical activity (synchronous changes in the cortex and hypothalamus). The parallelism between the increase release of acetylcholine and the bioelectrical changes continued until the time of the peak effect of centrophenoxine (45 min), followed by dissociation between them (the level of the released acetylcholine gradually approached the initial level, while the changed bioelectrical activity persisted for a longer time.

Acetylcholine↗
PubMed1979

Participation of adrenergic mechanisms in brain acetylcholine release produced by centrophenoxine.

The effect of phentolamine (alpha-adrenoceptor antagonist) and propranolol (beta-adrenoceptor antagonist) on the increased brain acetylcholine-releasing effect of centrophenoxine were studied in unanaesthetized cats in which perfusion of the anterior horn of a lateral cerebral ventricle was performed. Phentolamine alone decreased the amount of spontaneously released acetylcholine and did not change the effect of centrophenoxine. Propranolol alone did not change the amount of spontaneously released acetylcholine and reversed the centrophenoxine effect. The effects of centrophenoxine on acetylcholine release are attributed to its action on the presynaptic adrenoceptors (alpha and beta) situated in the cholinergic terminals of structures lying the anterior horn of a lateral cerebral ventricle.

Acetylcholine↗
PubMed1979

Ontogenetic development of 3,5-adenosine monophosphate phosphodiesterase in guinea pig and rat ileum.

The postnatal development of phosphodiesterases with low and high Michaelis constants in guinea pig and rat ileum was studied. The tow types of phosphodiesterases were found to increase their activity post partum, and this increase was particulary pronounced in the rat. The rise in the enzyme activity took place mainly at the expense of the increase of the phosphodiesterase with high Km. In addition to the quantitative differences in the phosphodiesterase activity of yound and adult animals, considerable age differences were also observed in the sensitivity of the enzyme to inhibitors and activators. These data can contribute to the explanation of the differences in the action of some drugs influencing the phosphodiesterase in young and adult organisms.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1979

Behavioural reactions and changes in the spontaneous and evoked EEG-activity upon microinjection of noradrenaline and isoprenaline in cat nucleus raphe dorsalis.

Experiments are carried out on five cats with bipolar electrodes chronically implanted in various brain structures. The electrode intended to be introduced into raphe dorsalis is placed in a "guiding" isolated cannule. The spontaneous EEG-activity, the evoked potentials of photo- and electrostimulation as well as the behavioural reactions are studied for each animal before and after administration of noradrenaline (NA), isoprenaline (ISO) respectively, into nucleus raphe dorsalis (RD). The evoked potential are tape-recorded and averaged on Nicolet--1072 computer. Administration of NA in cat RD is followed by manifestations characterized by vegetative and motor symptoms and accompanied by EEG-changes. Desynchronization develops immediately after the injection of both NA and ISO in RD. The restoration of the amplitude-frequency characteristics of the EEG-activity take place in RD at the latest. Considerable changes are also observed in the evoked potentials recorded from the different structures. The EEG-changes observed after injection of NA, respectively ISO, in RD suggest functional connections between RD and the other brain structures studied. Both the EEG-changes and the observed behavioural reactions are probably largely based on the inhibition of the cerebral serotonin tonus by the catecholamines NA and ISO injected into RD and the resulting disruption of the balance between the adrenergic and serotoninergic cerebral systems.

Amygdala↗