[STUDYING SOME PHARMACOLOGICAL EFFECTS OF NEW 3-HYDROXYPYRIDINE DERIVATIVE].

It was established that a new 3-hydroxypyridine (3-HP) derivative, 2-ethyl-6-methyl-3-hydroxypyridine L-aspartate (3-HP), in small doses (1 and 5 mg/kg) increased physical performance in treadmill and swimming tests on rats. The new substance showed greater or equal effects compared to the reference actoprotector drugs metaprot and ladasten in much higher doses. The gluconeogenesis inhibitor tryptophan significantly (74 ± 5%, p < 0.01) prevented this stimulatory effect of 3-HPA in the treadmill test on rats. 3-HPA at a higher dose (30 mg/kg) had marked antiamnesic effect on various models of amnesia in mice. It was more effective than reference drugs mexidol (another 3-HP derivative) in a dose of 30 mg/kg and nootropic drug piracetam in a dose of 200 mg/kg, but had equal effect with these drugs in doses of 50 and 800 mg/kg, respectively. 3-HPA (30 mg/kg per day) had neuroprotective effect in rats with brain ischemia and decreased the neurologic deficiency more effectively than mexidol (50 mg/kg per day).

ACTION OF NEW 3-HYDROXYPYRIDINE DERIVATIVES WITH ANTI-NAUPATHIA PROPERTIES ON CENTRAL NEURONS.

Experiments with cats showed that microinjections into the lung of new 3-hydroxypyridine derivatives SK-119 and IBKhF-27 had a direct action on 50 and 84 % of medial vestibular nucleus (MVN) neurons respectively. The inhibitory response to the compounds was observed 6 and 25 times more frequently than exciting; inhibition by IBKhF-27 was observed 1.9 times more frequently than by SK-119. Also, microinjections of SK-1 19 and IBKhF-27 acted directly on 44 % and 81 % of cat's Purkinje cells, respectively. In case of Purkinje cells, the inhibitory reaction was seen 5.5 and 25 times oftener than exciting, respectively, and inhibition by IBKhF-27 occurred 2.1 times more frequently than by SK-119. Investigations of rat's cerebellum sections evidenced that 5 mM of IBKhF-27 inhibited population responses of Purkinje cells 95 1 3 %. In the presence of specific noncompetitive NMDA-receptor antagonist (MK-801, 100 pM) the depressive effect was annulled almost fully by 96 * 2 %. It follows that IBKhF-27 nearly entirely inhibits synaptic transmission from cerebellar parallel fibers to Purkinje cells, while MK-801 has a similarly strong anti-depression effect that testifies the involvement of the NMDA-receptor complex predominantly.

[A new approach to the search for vestibuloprotectors].

The results of experimental clinical testing of the antinaupathia action of as new compounds, so motion sickness medications (promethazine, ikaron-1 etc.) are presented. Russian medication mexidol, a derivative of 3-hydroxypyridine (3-HP) demonstrated the ability to control motion sickness in humans and animals; however, unlike reference vestibuloprotector scopolamine, it does not practically produce side-effects. Mexidol acts through ion pathways with the involvement of glutamate and GABA-ergic components. Revealed 9 of new 3-HP derivates with an antimotion sickness effect in rats, three exceeded in efficacy mexidol, and also reference medications (i.e. scopolamine and promethazine). Melatonin achieves a better vestiboloprotective effect in rats than promethazine and melatonin-ergic antidepressant agomelatine through the involvement of melatonin MT1-, MT2- and GABA(A)-receptors. Also, combinations of melatonin with mexidol or promethazine possess a distinct vestibuloprotective effect, as melatonin enhances the action of equally mexidol and promethazine. Analysis of our results and investigations of other authors infer that search for potent vestibuloprotectors should be extended to new 3-HP derivatives and melatoninergic compounds. Individual medications by themselves and in combinations can become a solution to the problem.

[VESTIBULAR AND THERMOPROTECTIVE PROPERTIES OF A NEW ACTOPROTECTOR].

In experiments with rats, a new 3-hydroxypyridine (3-HP) derivative--2-ethyl-6-methyl-3-hydroxypyridine L-asparaginate (30 mg/kg)--exhibited a strong vestibuloprotective effect which was better than of promethazine (50 mg/kg), a well-known vestibuloprotector Besides the new actoprotector was competitive with another 3-HP derivative, namely, mexidol (ethyl-methyl-hydroxypyridine succinate) (100 mg/kg). Moreover, a distinct thermoprotective effect of 2-ethyl-6-methyl-3-hydroxypyridine L-asparaginate (30 mg/kg) in mice was not worse than that of mexidol or metaprot (ethylthiobenzimidasol, former name bimethy), an actoprotector with good thermoprotective properties. To conclude, owing to the membrane-protective and antioxidative qualities, the vestibuloprotective and thermoprotective properties of 2-ethyl-6-methyl-3-hydroxypyridine L-asparaginate are better or competitive with the reference preparations.

[STUDIES OF THE ANTIHYPOXIC AND ANTIAMNESTIC EFFECTS OF MELATONIN IN ANIMALS].

Experiments with mice showed that in a multitude of acute hypoxia models (normobaric hypoxic hypoxia with hypercapnia, hypobaric, hemic and histotaxic) the antihypoxic action of a single intra-abdominal dose of melatonin surpasses greatly amtisol, the standard antihypoxic agent. Single melatonin injection produced a strong antiamnestic action on various amnestic models (scopolamine-induced, acute normobaric hypoxia with hypercapnia, and a combination of extreme factors) which was much better than of pyracetame, a well-known nootropic (mind-stimulating) drug. Increase of the melatonin dose from 1 mg/kg to 20 mg/kg amplified both the antihypoxic and antiamnestic effects. Melatonin inhibited orthodromal population responses in surviving sections of rat's hippocampus (by 24 ± 3% at 2 mM; by 72 ± 6% at 5 mM). Besides, the inhibiting action of lusindol, a blocker of melatonin receptors MT1 and MT2--was virtually fully neutralized. Therefore, melatonin inhibits transmission within the Schaffer collateral--CA1 pyramidal neurons synapse by stimulation of melatonin receptors MT1 and MT2; higher melatonin concentrations (0.5 to 5 mM) enhance its effectiveness.

[Study of some pharmacological properties of a new adenine derivative].

It is established that the new compound, 9-[2-(4-isopropylphenoxy)ethyl]adenine (9-IPE-adenine) in a dose of 10 mg/kg per day produces neuroprotective effect in rats with brain ischemia model. 9-IPE-adenine decreased the neurologic deficiency 1.2 times more effectively (p < 0.05) than the reference drug mexidol in analogous dose, and had equal effect with this drug at 25 mg/kg per day on the neurologic deficiency and survival of animals. Electrophysiological studies in hippocampal slices in rats showed that 9-IPE-adenine depressed orthodromic population spikes in CA1 area by 42 ± 4%. Non-competitive antagonist of NMDA receptor complex MK-801, in contrast to D-AP5 (competitive NMDA receptor antagonist) and CNQX (competitive AMPA receptor antagonist), enhanced the depressive effect of the new drug more than two times. These ese results are indicative of the ability of 9-IPE-adenine to modulate the ion channel of NMDA receptor complex.

[Investigation into the vestibular protective properties of melatoninergic agents].

Experiments with rats showed that melatonin (2.5 mg/kg) produces a distinct vestibular protective effect excelling promethazine (50 mg/kg) as a reference agent, and also antidepressant agomelatine (5 mg/kg) as another melatoninergic agent. Lusindol, a blocker of MT1/MT2-receptors (2.5 mg/kg), and bicuculline (1.5 mg/kg), a specific GABA-receptors antagonist, weakened the melatonin effect significantly. The results testify mediation of the melatonin action by these receptors. Whole-cell patch clamp in an experiment with convoluted oblongata sections from white nonlinear infant male rats (14-d old) disclosed that melatonin (2 mM) inhibited drastically (29 +/- 3%) the excitatory postsynaptic current caused by depolarization step in neurons of the medial vestibular nucleus. Lusindol (0.1 mM) inhibited the effect of melatonin (2 mM) significantly (71 +/- 6%) which suggests involvement of melatonin MT1/MT2-receptors.

[Effects of vestibuloprotectors mexidol and melatonin on animal cerebellum].

In experiments with cats, air-assisted microinjections of mexidol and melatonin had a direct effect on 71-81% Purkinje cells inducing the inhibitory response 4.2-6.3 times more often than exiting. In case of concurrent action of MK-801 (a specific noncompetitive NMDA-receptor antagonist) the mexidol effect on the spontaneous activity was suppressed fully or abated significantly in 88% Purkinje cells. Lusindol (a specific melatonin MT2- and MT2-receptor antagonist) and GABA-negative bicuculline prevented the inhibiting effect of melatonin fully or abated significantly the spontaneous activity of 86% and 71% Purkinje cells, respectively. This means that melatonin-produced inhibition recruits both melatonin MT1- and MT2-receptors, and also the GABA-ergic component (stimulation of GABAA-receptors). Investigation of rat's cerebellum slices with prolonged survival showed that 5 mM of mexidol inhibited reliably Purkinje cells population responses by 93 +/- 4%; the presence of MK-801 (100 microMM) weakened this effect by 82 +/- 3%. Consequently, mexidol is capable to inhibit strongly the parallel fibers--Purkinje cells synaptic transmission in the rat's cerebellum, whereas MK- 801 abates this effect appreciably.

[On the mechanism of ikaron-1 anti-naupathia action].

Pneumomicroinjection of vestibuloprotector ikaron-1 (Russia) in specific neurons of the medial vestibular nucleus (MVN) was studied in cats immobilized by muscle relaxants using microelectrode devices. The original preparation had a direct effect on the majority of MVN neurons (95 %). Thirty four neurons of 37 cells (92 %) developed an inhibitory response, only one cell (3 %) was activated and 2 neurons (5 %) were areactive. Therefore, the inhibitory reaction to the preparation was 34 times more often than excitatory. An investigation of the MVN neurons activity evoked by adequate stimulation of the vestibular apparatus showed that ikaron-1 attenuates the evoked response in 92 % cells. This phenomenon could be behind the ikaron-lantinaupathia action.

[Analgesic effect of succinate-containing preparations].

It was established that mexidol (100 mg/kg, i.v.) in contrast to cytoflavin (1 ml/kg, i.v.) and reamberin (100 mg/kg, i.v.) produced analgesic effect in rabbits by raising pain threshold under electric stimulation of dental pulp. Mexidol (200 mg/kg, i.p.) also raised the nociceptive threshold of the same tail stimulation by in rats (vocalization test). Non-competitive antagonist of NMDA receptor complex, MK-801 (0.1 mg/kg, i.p.), and selective GABAA receptor antagonist bicuculline (1.5 mg/kg, i.p.) decrease the effect of mexidol. Therefore, the antinociceptive effect of mexidol in rats is mediated by the NMDA receptor complex and GABAA receptors. It was also found that mexidol (microiontophoretic application) produced inhibiting effect on spontaneous and evoked (caused by nociceptive electric stimulation of hind paw) activity of neurons (major part) of sensorimotor cortex and ventral posterior thalamic nucleus in rabbits. On the background of MK-801 and GABA blockers (bicuculline and picrotoxin), this action of mexidol was completely prevented or considerably decreased (by almost 80 and 60% of cells, respectively). Therefore, the effect of mexidol on these neurons is realized by inhibiting ion currents through NMDA receptor complex and via GABAA/benzodiazepine receptor complex.

[Electrophysiological study of the mechanism of mexidol action].

It has been found that mexidol (5 mM) significantly (96 +/- 2%) depressed excitatory postsynaptic current caused by step depolarization in neurons of medial vestibular nucleus of medulla oblongata slices in young (aged 13 - 17 days) male albino rats. In addition, mexidol (2,5 - 5 mM) depressed by 94 +/- 3% excitatory postsynaptic current caused by Shaffer collaterals stimulation of CA1 pyramidal neurons of hippocampal slices in young rats. Complex MK-801 (non-competitive antagonist of NMDA receptors), in contrast to CNQX (competitive AMPA receptor antagonist), considerably decreased the depressant effect of the drug in both brain structures. Therefore, the central favorable effect of mexidol can be mediated by ion mechanisms with glutamate- and GABA-ergic components, primarily by the inhibition of ion currents through NMDA receptor complex.

[Comparative studies of antihypoxic, neuroprotective and analgesic action of succinate-containing drugs].

Experiments with mice showed that, unlike reamberin (100 mg/kg), mexidol (100 mg/kg) and cytoflavin (1 ml/kg) act as antihypoxants in pressure and hermetic chambers but not in case of acute hemic and histotoxic hypoxia. Amtisol succinate (100 mg/kg), a reference antihypoxant, excels the other tried succinate-containing drugs in all models of acute hypoxia except the hermetic chamber. In addition, the neuroprotective action of mexidol (100 mg/kg/d) and cytoflavin (100 ml/kg/d) in rats with induced ischemic stroke which was stronger than that of reamberin and amtisol succinate (100 mg/kg/d). Besides, mexidol (100 mg/kg) but not cytoflavin (1 ml/kg), reamberin or amtisol succinate (100 mg/kg) had a distinct analgesic effect in rabbits. On the neuronal level, mexidol interacts with the GABAA- benzodiazepine-receptor complex in nearly 60% cells and inhibits ion currents through the NMDA-receptor ion channels in nearly 80% neurons.

[Effects of different neuromediators and regulatory peptides on the impulse activity of neurons in the superior vestibular nucleus].

The microelectrode technique and microiontophoresis of physiologically active substances in experiments with cats immobilized with the muscle relaxants made it clear that different classical neuromediators (acetylcholine, norepinephrine, gamma-aminobutyric acid (GABA) and others), as well as regulatory peptides (enkephalins, thyrotropin-releasing hormone (TRH), vasoactive interstitial peptide (VIP), somatostatin (SS) and others) can exert a direct effect on the majority (61 to 100%) of neurons in the superior vestibular nucleus (SVN). The inhibiting effect of enkephalins, VIP and SS on the neurons impulse activity remained essentially unchanged by L-glutamate. Also, enkephalins, VIP and SS were found to amplify the inhibiting action of GABA and glycine. Consequently, these substances can fulfill the role of SVN neuromediators and/or neuromodulators.

[Actiprotective and antihypoxic action of new heteroaromatic antioxidants].

Expernents with mice showed that most of 15 new heteroaromatic antioxidant compounds possess aciprotective and antixopixic properties. Based on results of treadmill and swimming tests, actiprotective action of IBKhF-1, 11 and 14 surpassed greatly bemythil and bromanthane in ordinary conditions. Inhibitor of gluconeogenase tryptophan cancelled largely the stimulatting action of highly effective and active IBKhF-1, 2 and 11 on physical performance during treadmill exercise. Consequently, gluconeogenesis activation is one of the major components of the actiprotective action of these antioxidants. In addition, IBKhF-1, 11 and 14 excelled bemythil and bromanthane in the extreme conditions of running in hyperthermia and swimming in acute hypoxia combined with hypercapnia. IBKhF-2 and 14 were better than amtisol (standard antihypoxic agent) and bemythil against acute hypoxia in pressure chamber, whereas IBKhF-4 and 14 excelled these agents in thermal chamber.

[Investigation of anti-hypoxic action of 3-hydroxypyridine derivatives in animals with some types of experimental pathology].

Experiments with occlusion of the common carotid artery in mice demonstrated that, unlike mexidol and SK-170, single injection of new derivatives of 3-hydroxypyridine (3-HP) SK-100 and IBKhF-2, and semax have an anti-hypoxic action on the model of acute normobaric hypoxia with hypercapnia. In analogous experiments with rats the distinct anti-hypoxic action was produced by 4 new 3-HP derivatives (SK-100, SK-170, IBKhF-22 at the dose of 100 mg/kg and IBKhF-2 at the doses of 10 and 30 mg/kg--extension of life span by 25-39%), mexidol (100 mg/kg) and reference-class antihypoxant amtisol (30 mg/kg, life span expansion by 19 and 27%, respectively). A series of experiments with rats with acute pancreatitis, a distinct anti-hypoxic action was shown by SK-100, SK-170 at 100 mg/kg and IBKhF at 10 and 30 mg/kg (life span extension by 26-40%), mexidol (100 mg/kg) and amtisol (30 mg/kg) which extended life span by 17 and 22%, respectively. Therefore, SK-100 and IBKhF-2 are potent to prolong life span of equally mice and rats; SK-170 and mexidol were effective only in experiments with rats.

[Indralin--a novel effective radioprotector during irradiation by high-energy protons].

Experiments with 120 mongrel dogs were aimed at the assessment of radio protective strength of indralin and local shielding of the pelvic marrow from 2.5 Gy, and also their concurrent use for the dogs irradiated by protons (240 MeV) at absolutely lethal and over-lethal 4 Gy and 5 Gy. Clinical observations, hematological investigations and ECG analysis of survived animals were conducted 4.5 years post the irradiation. Dogs that remained healthy following 3.5 to 4.5 years since the irradiation were sacrificed for pathomorphological investigations. The radioprotective effect of local shielding against 4 Gy was weak while this effect of intramuscular indralin (10, 20, 40 mg/kg of body) was significant reaching 50 to 67.7%. The concurrent use of two methods had, apparently, potentiated the 100% radioprotection of the animals irradiated by overlethal 5 Gy. Blood investigations of the survived dogs every 2-4 months evidenced that complete recovery of the total leukocyte count had taken 9 to 13 months. Also, dogs' pregnancy in 9-10 months since the beginning of irradiation pointed to maintenance of fertility and the ability to parturiate 2 or 3 times yielding 5-6 live cubs. Necropsy of the dogs did not reveal gross macroscopic structural changes of visceral organs or tissues. Seven out of 27 sacrificed dogs had benign tumors infrequent in intact dogs at this age.

[Effects of different neuromediators and regulatory peptides on the impulse activity of neurons in vestibular zone-I of the cerebral cortex].

Microelectrodes and micro-iontophoresis of physiologically active substances in experiments with cats immobilized by muscle relaxants made it apparent that different classical neuromediators (acetylcholine, norepinephrine, GABA and others) and regulatory peptides (enkephalins, thyrotropin-releasing hormone, vasoactive intestinal peptide (VIP), somatostatin (SS) and others) are capable to influence directly 68 to 100% of neurons in vestibular zone-I of the cerebral cortex. In the presence of L-glutamate, the inhibiting effect of enkephalins, VIP and SS on the neurons impulse activity was essentially unaltered. Also it was shown that enkephalins, VIP and SS are potent to augment the inhibiting effect of GABA and glycine. Therefore, these substances may have the neuromediator and/or neuromodulator role in this cortical zone.

[Effects of various neuromediators and regulatory peptides on the impulse activity of neurons in the lateral vestibular nucleus].

The myoelectrode technique and microiontophoresis of physiologically active substances were applied to cats immobilized with neuromuscular relaxant to show that the classic neuromediators (acetylcholine, norepinephrine, GABA etc.) and regulatory peptides (enkephalins, TRHs, vasoactive intestinal peptide (VIP), somatostatin (SS) and others) can influence directly most neurons (58 to 100%) in the lateral vestibular nucleus (LVN). Enkephalins, VIP and SS retained largely their inhibitory effect on the neuron impulse activity in the presence of L-glutamate. Also, enkephalins, VIP and SS are able to stimulate or suppress the inhibitory effect of GABA and glycine. Consequently, the substances under study may act as LVN neuromediators and/or neuromodulators.

[Evaluation of antihypoxic and antiamnemonic effects of mexicor in animals].

In experiments with mice closed in airtight and altitude chambers mexicor effectiveness against hypoxia was evident only at the dose of 100 mg/kg; effect was nil against acute hemic and histotoxic hypoxia. The reference antihypoxic substance (amtisol succinate, 25-100 mg/kg) excelled mexicor in all models of acute hypoxia. In the model of cerebral infarct in rats, the mexicor neuroprotective effect at the doses from 12.5 to 100 mg/kg was dose-dependent with a nearly linear trend and significantly stronger as compared to amtisol succinate. In amnesia models in mice the antimnemonic effect of the drug at the dose of 50-100 mg/kg was much stronger than of amtisol succinate and comparable to commonly used pyracetam and oxiracetam. Mexicor (5 mM per 53 +/- 4%, 10 mM per 94 +/- 6%) inhibited the orthodromic population response in survival sections of hippocampal CA1 in rats. Stimulation of respiration of isolated mitochondria from rat's cerebral cells showed linear dose dependence in the range from 1 mM to 5 mM. It can be concluded that the antihypoxic, neuroprotective and antiamnemonic action is achievable with high mexicor dosage.

[Modification by various neuromediators and regulatory peptides of the impulsation activity of neurons in the medial vestibular nucleus].

Cats were immobilized with myorelaxation agents to apply the microelectrode technique and microlonophoresis of physiologically active substances. As a result it was shown that various classic neuromediators (GABA, taurine and others) and regulatory peptides (vasoactive intestinal peptide (VIP), somatostatine (SS) and others) have effect on the majority (62 to 100%) of neurons in the medial vestibular nucleus. In the presence of L-glutamate VIP and SS CC retained essentially their inhibitory effect on the neurons impulse activity. Both VIP and SS were found to amplify the inhibitory action of GABA and glycine. To sum up, the substances under study can function as neuromediators and/or neuromodulators in the medial vestibular nucleus.