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S Todorov

Publications and source records attributed to S Todorov.

At least 37 records · Page 2Linked to original sources
PubMed1990

Study of the effects of nootropic agents on the adrenergic neurotransmission in smooth muscles of young and old animals.

The effects of compounds from the group of nootropic agents on the peripheral adrenergic neurotransmission in animals of different ages were studied in in vitro experiments. The experiments were performed on smooth muscle preparations isolated from young sexually mature (4-5-month-old) and old (22 month-old) rats treated twice daily for 7 days with 50 mg/kg of the nootropic agents piracetam, its structural analogues p-H and p-Cl, aniracetam and Ginseng extract. The animals were decapitated on the 7th day, the changes in the contractile responses of the smooth muscles to noradrenaline (NA) or electrical stimulation (ES) were studied in isolated preparations from vas deferens, aorta and anococcygeal muscle. The results show that the compounds studied can modulate the contractile effects of NA and ES, their action being most often potentiating and more pronounced in the smooth muscles manifesting weaker responses. In some cases the reactivity of the smooth muscle preparations to the stimuli applied was reduced after the nootropic agents. These effects can be partly explained with changes in the sensitivity of the pre- and postsynaptic alpha-adrenergic receptors. The possible variabilities in the influence on the two receptor populations in the different smooth muscles could explain the differences in the observed modulatory effects of the nootropic agents. The data obtained show that in prolonged therapeutic application of nootropic agents it is necessary to bear also in mind their possible influence on the peripheral neurotransmitter systems.

Aging↗
PubMed1989

In situ effects of histaminergic agents on adrenergic neurotransmission in rat mesenteric microcirculation.

Experiments were performed to study in situ the effects of histamine and some H1- or H2-agonists and antagonists on the contractions of the rat mesenteric methaarterioles (RMMA) induced by 0.6 nM noradrenaline (NA) applied locally or by electrical stimulation (ES). All drugs tested (cimetidine--300 nM, the others --30 nM) were also applied locally 30 s before the contractile stimulus. NA and ES strongly contracted the blood vessels. Of all drugs studied only diphenhydramine (DPH) evoked a slight contraction of RMMA. Histamine markedly inhibited the contractile responses to NA and ES. Similar effects were exerted by 2-(2-aminoethyl)thiazole (2-AET) its inhibitory action on the ES-induced contractions being weaker than that of histamine. Dimaprit (DMP) only tended to inhibit the RMMA contractions. DPH abolished the NA-induced contractions while cimetidine (CIM) did not change the effects of NA and ES. The results suggest that H1-receptors are mainly involved in the modifying action of histaminergic drugs on the adrenergic neurotransmission in RMMA.

Animals↗
PubMed1988

Smooth-muscle effects of substance P.

The effects of substance P (SP) on smooth-muscle contractions induced by noradrenaline (NA) or by high- or low-frequency electrical stimulation (ES) were studied on isolated rat vas deferens and musculus anococcygeus. Neither the contractile effects of NA nor those of high-frequency ES were significantly changed by SP. The peptide in concentrations of 1 x 10(-7) M and 1 x 10(-6) M strongly potentiated (up to 70%) vas deferens contractions in response to low-frequency ES but slightly reduced those of musculus anococcygeus. Inhibition of the opiate receptors by 1 x 10(-6) M naloxone did not change the potentiating SP-effect on vas deferens contractions. Blockade of the prostaglandin (PG) receptors by polyphloretin phosphate (PPP), 5 micrograms/ml, or of the PGs synthesis by indomethacin, 5 x 10(-6) M, resulted in a slight increase of the SP-potentiating effect. The present results suggest that specific presynaptic SP-receptors (excitatory or inhibitory) play a major role in the mechanism of the potentiating action of substance P.

Animals↗
PubMed1988

Smooth-muscle effects of C-terminal tripeptide of substance P.

The effects of the C-terminal tripeptide fragment of substance P(SP-C-TP) and its interactions with substance P(SP) were studied on isolated smooth-muscle preparations (rat musculus anococcygeus and vas deferens and rabbit ear central artery). Like SP, SP-C-TP (1 x 10(-8) M-1 x 10(-4)M) potentiated contractions of vas deferens and musculus anococcygeus elicited by low frequency electrical stimulation (LFES), the effect of the fragment being much weaker than that of the neuropeptide. The potentiating effect of SP was strongly reduced by SP-C-TP. The fragment slightly decreased the noradrenaline (NA)-induced contractions of vas deferens only. When the pharmacological agents were applied extralumenally only high SP concentrations (1 x 10(-7)M and 1 x 10(-6)M) significantly potentiated the LFES-evoked smooth-muscle contractions. SP-induced potentiation was abolished by SP-C-TP. Intralumenal administration of the neuropeptide and its fragment always led to a marked inhibition of the LFES contractile effects. The observed effects suggest that SP-C-TP acts as a competitive dualist of SP. The data is interpreted in terms of the hypothesis that the neuropeptide fragments might perform as a natural antagonist of the peptides and may control their effects.

Animals↗
PubMed1988

Comparative studies on the effects of the nootropic drug adafenoxate and of the cerebral vasodilator flunarizine on arterial smooth muscles.

The effects of the nootropic drug adafenoxate and of the cerebral vasodilator flunarizine were studied on smooth-muscle preparations isolated from rabbits (perfused central ear artery and segments of the thoracic aorta). Both drugs tested did not change the smooth muscle tone. When applied extralumenally adafenoxate decreased the noradrenaline (NA)-evoked arterial contractions. Adafenoxate (especially in high concentrations) markedly relaxed the NA-contracted arterial preparations. The arterial contractions in response to low-frequency electrical stimulation (ES) were moderately potentiated by high concentrations of extralumenal adafenoxate, but were decreased by intralumenal administration of the drug. Administered prior to or after NA adafenoxate antagonized its contractile effects on the aortic segments (this effect was much pronounced when the smooth-muscle preparations were contracted by NA). Flunarizine exerted similar but less pronounced inhibitory effects on the NA- or ES-evoked contractions of the smooth-muscle preparations. The only essential difference between the two drugs tested was that extralumenal flunarizine inhibited the arterial contractions in response to ES. It is suggested that if adafenoxate exerts an antivasoconstrictory effect not only on the peripheral arteries but also on the cerebral blood vessels, this effect might play an important role for the realization of the nootropic action of this compound.

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

The role of H1- and H2-receptors in the modulatory effects of histaminergic agents on adrenergic neurotransmission in rat vas deferens.

The role of the H1- and H2-receptors in the modulatory effects of histamine and other histaminergic drugs on smooth muscle adrenergic neurotransmission was studied on isolated preparations from rat vas deferens. The typical biphasic action (potentiation by low concentrations and inhibition by high concentrations) of histamine and some H1- or H2-agonists on vas deferens contractions induced by low frequency electrical stimulation (ES) was markedly changed by H1- or H2-antagonists. After blockade of H1-receptors, the potentiating effect of histamine and the histaminergic agonists was diminished or even reversed. The inhibition of the smooth muscle contractions by the drugs tested was stronger after H1-antagonists. Blockade of H2-receptors usually enhanced the potentiating effect of the histaminergic agonists on ES-evoked vas deferens contractions. The inhibitory action of histamine and the histaminergic agents tested was decreased or even reversed after H2-receptor blockade. These results confirm the presence of H1-excitatory and H2-inhibitory receptors whose activation or inhibition can modulate adrenergic neurotransmission in vas deferens.

Animals↗
PubMed1986

[Embryotoxic and teratogenic action of phenylmercuric acetate (Falisan-Nassbeize)].

Tested was the embryotoxic and teratogenic action of the organic mercury compounds (phenyl mercuric acetate), containing 2 per cent mercury, on albino rats. The preparation was introduced orally during pregnancy in the form of a 2 per cent water solution at the following rates: I group--1/8 LD50 (= 4 mg Hg/kg body mass) on the 4th and 5th day of pregnancy; II group--1/3 LD50 (= 10 mg Hg/kg) on the 4th and 5th day too; III group--1/8 LD50 (= 4 mg Hg/kg) from the 3rd to the 19th day; IV group--control animals. The preparation proved to be highly toxic with the animals of the II group, with high mortality rate (42.85 per cent). No teratogenic effect with malformations was produced with the three test groups during embryogenesis.

Abnormalities, Drug-Induced↗
PubMed1985

Histaminergic agents can modulate adrenergic smooth muscle neurotransmission.

The effects of histamine and some agonists and antagonists of the two types of histaminergic receptors on adrenergic smooth muscle neurotransmission were studied. The experiments were carried out on electrical stimulated (0.1 Hz, 1 pulse, 1 msec pulse duration, supramaximal voltage) prostatic part of rat vasa deferentia. Histamine, 2-(aminoethyl) thiazole and 2-methylhistamine (H1-agonists) as well as dimaprit (H2-agonist) had a biphasic effect on smooth muscle contractions induced by electrical stimulation (ES): low drug concentrations potentiated and high concentrations markedly inhibited the ES-contractions. The agonist of H1-receptors pyridylethylamine in low concentrations did not affect the smooth muscle contractions and in high concentrations decreased their amplitude. Diphenhydramine and mepyramine (H1-antagonists) strongly potentiated (up to 250%) the ES-contractions, while the H2-antagonist cimetidine did not change them. These effects might be due to the interaction of the drugs tested with different populations of the histaminergic receptors.

Animals↗
PubMed1985

[Embryotoxic and teratogenic action of the organomercury fungicide falizan on chick embryos].

Tested was the embryotoxic and teratogenic action of the organomercurial preparation falizan (a phenyl-mercury acetate), containing 2 per cent mercury, in chick embryos. It was introduced into the viteline sac of 3-day-old embryos in the form of a water solution as follows: Group I--0.1 cm3 per egg of a 13 per cent solution of falizan (= 260 micrograms Hg); group II--0.1 cm3 per egg of a 6.5 per cent solution (= 130 micrograms Hg); group III--0.1 cm3 per egg of redistilled water (biologic control); and group IV--the eggs were left untreated (negative control). The amount of the preparation was adjusted to eggs of 65 + 1 g weight. The optimal growth and development of the embryos was guaranteed with the use of an Optima hatching unit, providing humidity of up to 65 per cent = 89 F. The embryotoxic and teratogenic effect of the preparation was recorded on the 14th and the 20th day of incubation. A dose of 260 micrograms Hg was found to be strongly toxic, mortality rate reaching up to 48 per cent from the 7th to the 14th day. Teratogenically, there were no malformations in the test groups both on the 14th and the 20th day of embryogenesis.

Abnormalities, Drug-Induced↗
PubMed1984

On the pharmacology of the ergot alkaloid elymoclavine.

Pharmacological investigations of the ergot alkaloid of the group of clavines, elymoclavine, isolated from Claviceps sp. cp. II showed the following results: The LD50 for mice for 24 h was 350 (228-535) mg/kg and for rats 145 (81-258) mg/kg. Elymoclavine induced a dose-dependent stereotypy (doses of 2 to 10 mg/kg) in rats and mice which was antagonized by haloperidol and pimozide. It prevented the development of haloperidol catalepsy in rats and produced rotations contralateral to the striatal lesions with 6-OHDA which were antagonized by pimozide and partly by cyproheptadine. Elymoclavine, like bromocriptine, decreased the plasma level of prolactin. Furthermore, elymoclavine increased the exploratory activity of rats in open field; this effect was antagonized by haloperidol and was essentially influenced by many substances acting on different transmitter systems (NA, DA, GABA). Elymoclavine inhibited the picrotoxin and electroshock convulsive seizures but potentiated the pentylenetetrazol ones in mice as these effects were differently influenced by pimozide, haloperidol, 5-HTP, atropine and phentolamine. 100 and 250 micrograms/kg of elymoclavine produced a considerable and persisting decrease of the blood pressure in anaesthetized cats. At 1 X 10(-6) M, without producing any per se effect, elyoclavine decreased the contractile effects of acetylcholine, nicotine, BaCl2 and PGE1 as well as the field electrical stimulation-induced contractions in an isolated segment from guinea-pig ileum. The observed effects of elymoclavine are mainly due to its dopaminergic agonist action. It seems, however, that influences on other transmitter receptors also underlie the mechanism of action of this ergot alkaloid.

Animals↗
PubMed1984

Experimental pharmacological study of three species from genus Salvia.

Fifteen extracts isolated from three species of genus Salvia were studied: two from Salvia officinalis, seven from Salvia triloba and six from Salvia verbenaca. Their effects on the blood pressure of cats and spontaneously hypertensive rats were examined. The smooth-muscle effects of the extracts were studied on isolated segments of guinea-pig ileum. The effects of some of the extracts on hexobarbital anaesthesia were investigated. Applied intravenously and duodenally, aqueous-alcohol extract of Salvia officinalis causes moderate but prolonged lowering of the blood pressure in cats. Decoction of Salvia triloba also possesses a similar effect (in experiments on spontaneously hypertensive rats). Most of the extracts isolated from Salvia officinalis and Salvia triloba inhibit to various degrees smooth-muscle contractions induced by acetylcholine, histamine, serotonin and BaCl2, whereas extracts of Salvia verbenaca usually potentiate them. Substances isolated from Salvia triloba prolong hexobarbital sleep. Future studies of substances isolated from Salvia officinalis and Salvia triloba are promising with a view to their spasmolytic and hypotensive actions. There exist marked interspecies differences in the pharmacological effects of biologically active substances isolated from genus Salvia.

Anesthesia↗