Synthesis and pharmacological activity of new carbonyl derivatives of 1-aryl-2-iminoimidazolidine. Part 1. Synthesis and pharmacological activity of chain derivatives of 1-aryl-2-iminoimidazolidine containing urea moiety.

The synthesis and physicochemical properties of new carbonyl derivatives of 1-aryl-2-iminoimidazolidine are presented. Isomeric 1-(1-arylimidazolidine-2-ylidene)-3-arylureas (series A) and 1-aryl-2-imine-3-arylaminocarbonylimidazolidines (series B) were obtained after the condensation reaction of 1-aryl-2-iminoimidazolidines and arylisocyanates. 1-Aryl-2-iminoimidazolidines were synthesised in a two-step reaction from the respective anilines. The molecular structure of 1-(1-phenylimidazolidine-2-ylidene)-3-(4-chlorophenyl)urea (A2) has been determined by X-ray crystallography. The representatives of both investigated series were evaluated in behavioural animal tests. They exhibited significant, especially analgesic, activity on the animal central nervous system (CNS). They displayed substantial effect on the serotonine and catecholamine neurotransmission as well, at very low toxicity (LD(50) over 2000 mg kg(-1) i.p.). In the binding affinity tests they exhibited moderate affinity (on the micromolar level) toward opioid (mu) and serotonine (5HT(2)) receptors. The derivatives of series A had moderate affinity toward benzodiazepine (BZD) receptor as well. Distinctive differences observed in their activity spectra can be connected with the presence of particular structural features such as relative orientation of the two aromatic rings and the carbonyl moiety.

Influence of opioid receptor antagonists on motor-impairing effects of benzodiazepines.

The influence of naloxone and naltrexone on the motor-impairing effects of diazepam, chlordiazepoxide, clonazepam and estazolam were studied in the aerial righting reflex test (mice, rats), and the first two drugs were examined in the rota-rod test (mice). Benzodiazepine-induced motor incoordination was significantly decreased by naloxone and naltrexone (4-16 mg/kg) in mice and rats in aerial righting reflex test. The motor-impairing effects of diazepam and chlordiazepoxide observed in rota-rod test were significantly diminished only by naltrexone (8-16 mg/kg). These data seem to confirm some interactions between benzodiazepines and opioid system.

Studies on the antinociceptive effects of sodium nitroprusside and molsidomine in mice.

The participation of nitric oxide (NO) in antinociceptive activity of molsidomine and sodium nitroprusside (SNP) was studied in mice using the writhing test. Molsidomine (300 and 150 mg/kg) and SNP (1.52-0.38 mg/kg) induced antinociception that was antagonized by naloxone. L-arginine (500-62.5 mg/kg) did not produce antinociceptive effects, whereas N omega-nitro-L-arginine methyl ester (L-NAME) (37.5-150 mg/kg) induced antinociception which was suppressed by naloxone. Methylene blue did not change the molsidomine- and SNP-induced antinociception, but significantly intensified that produced by L-NAME. L-arginine increased antinociceptive effect of molsidomine but not that of SNP. Antinociceptive activity of L-NAME was partially reversed by L-arginine. D-arginine failed to influence these effects. The present findings suggest that the NO-cGMP pathway is not involved in the mechanism of molsidomine- and SNP-induced antinociception in the writhing test in mice.

Effects of opioid antagonists on anticonvulsant and hypnotic activity of benzodiazepines.

The influence of naloxone and naltrexone on the hypnotic and protective efficacy of diazepam, chlordiazepoxide, clonazepam and estazolam against electroshock- and pentylenetetrazole-induced seizures was studied in mice. Naloxone and naltrexone significantly decreased the anticonvulsant effects of diazepam and estazolam, but they did not changed that of chlordiazepoxide and clonazepam in electroshock-induced tonic hindlimb extension. Protective effects of benzodiazepines against pentylenetetrazole-induced seizures were slightly diminished by naloxone and naltrexone (16 mg/kg). Opioid antagonists were able to reduce the duration of benzodiazepines-induced sleep at high dose (32 mg/kg) only. These findings suggest that the endogenous opioid system may participate in antiepileptic effects of benzodiazepines but not in their hypnotic activity.

Ethanol and benzodiazepines. The influence of CGS 8216 on the ethanol-induced hypothermia and motor incoordination in mice and rats.

Ethanol has pharmacological profile very similar to benzodiazepines which facilitate GABA-ergic neurotransmission. In addition, a lot of ethanol-induced effects are partially antagonized by Ro 15-4513, a benzodiazepine inverse agonist. In our study, the influence of CGS 8216, another benzodiazepine inverse agonist, on the hypothermic (3.5 g/kg in mice, 3.0 g/kg in rats) and disturbing the motor coordination (3.2 g/kg in mice, 2.5 g/kg in rats, aerial righting reflex) effects of ethanol was investigated. The hypothermic effects of ethanol were antagonized in mice, and significantly attenuated in rats by CGS 8216 (10 and 20 mg/kg). Ethanol-induced motor incoordination was significantly diminished by 10 and 20 mg/kg of CGS 8216 in mice but not in rats. These data suggest that some effects of ethanol may result from the intensification of benzodiazepine/GABA-ergic activity. In addition, they let us presume that the activity of CGS 8216 is connected with a benzodiazepine receptor named BZ-1 or omega 1. The results indicate the need of further work on the benzodiazepine inverse agonists for use in treatment of ethanol poisoning.

Effect of life-long hypocaloric diet on age-related changes in motor and cognitive behavior in a rat population.

Aged (24 months), adult (12 months), and young (4 months) rats kept on standard or hypocaloric diets from the age of three weeks old were tested in a range of behavioral tests to determine the effects of aging on sensory-motor and cognitive behavior and to assess whether such effects were prevented by life-long calorie restriction. An age-related deterioration of sensory-motor functions, motility and exploratory activity was observed in all the senescent animals independent of diet. Swimming ability did not deteriorate with age. Spatial memory, evaluated by the Morris water maze test, showed some deterioration in normally fed adult rats as indicated by the deceleration in the learning curve. In aged rats, not only was learning slowed down, but memory utilization was also impaired. These cognitive deficiencies were absent in rats fed the hypocaloric diet.

Interaction between ketamine and ethanol in rats and mice.

The development of tolerance to analgesic effects of ethanol and ketamine, development of cross-tolerance between those drugs, and the effects of ketamine on the symptoms of ethanol abstinence were investigated in mice and rats. The analgesic action of ethanol (2.8 g/kg in rats, 5 g/kg in mice) was significantly reduced in the animals chronically treated with ethanol. Chronic treatment with ketamine (100 mg/kg in rats, 160 mg/kg in mice twice daily for 7 days) resulted in development of tolerance to the analgesic effects of ketamine. Cross-tolerance developed to the analgesic action of ketamine in mice and rats receiving ethanol chronically. A chronic treatment with ketamine resulted in development of significant cross-tolerance to the antinociceptive action of ethanol. Ketamine significantly attenuated the symptoms of ethanol abstinence (head shakes) in mice (20 mg/kg) and rats (25 mg/kg). Naloxone pretreatment (2 mg/kg) antagonized the inhibitory action of ketamine on the ethanol abstinence in rats. Doses of 12.5-75 mg/kg of ketamine abolished or significantly inhibited the ethanol abstinence symptoms (audiogenic seizures) in rats. The results demonstrate some similarities of the action of ketamine and ethanol and suggest a possibility that the endogenous opioid system participates in the mechanisms of action of the investigated compounds.

Opioid mechanisms of some behavioral effects of ketamine.

The effect of naloxone on the duration of sleep and on analgesia produced by ketamine, and on the development of tolerance and cross-tolerance with morphine to ketamine analgesic effects were investigated in mice. Ketamine produced a dose-dependent analgesia. Naloxone (4 mg/kg) significantly inhibited the analgesic effects of ketamine (40 mg/kg), but (given in a dose of 2 mg/kg) did not affect the duration of ketamine sleep. Chronic administration of ketamine (160 mg/kg twice daily for 7 days) resulted in a gradual shortening of ketamine sleep and in the development of tolerance to the analgesic action of ketamine. There also developed cross-tolerance between analgesic effects of morphine and ketamine. Ketamine (20 mg/kg) significantly inhibited symptoms of morphine abstinence produced in morphine-pelleted mice by naloxone administration or by pellet removal. The results suggest that at least some elements of the mechanism of action of ketamine and morphine may be common and related to the endogenous opioid system.

Interactions of ketamine, naloxone and morphine in the rat.

The effect of naloxone on the ketamine-induced anesthesia and analgesia, and the development of tolerance to ketamine and the cross-tolerance to morphine (measured by an analgesic effect) were investigated in the rat. Ketamine produced a dose-dependent analgesia. Naloxone, 1 mg/kg, significantly inhibited analgesia induced by ketamine, 100 mg/kg, but even in a dose of 4 mg/kg it did not affect the duration of anesthesia. A chronic administration of ketamine (100 mg/kg twice a day (b.i.d.) for 7 days) resulted in the development of tolerance to analgesic effects of ketamine. The analgesic action of morphine was attenuated in rats receiving ketamine chronically, while the analgesic effects of ketamine were significantly potentiated in morphine-dependent rats. Ketamine, 25 mg/kg, significantly attenuated the withdrawal signs evoked by naloxone in morphine-dependent rats. The results corroborate the suggestion about the participation of the central opioid neurotransmission in the mechanism of ketamine action.

Ethanol-induced hypothermia. Cross tolerance with morphine.

The development of tolerance to ethanol-induced hypothermia and hypnosis, and cross-tolerance with morphine was studied in mice and rats. Ethanol significantly decreased the body temperature in rats (3.0 and 3.2 g/kg) and in mice (3.5 and 4.0 g/kg). Chronic administration of ethanol resulted in the tolerance not only to ethanol hypothermia but also to hypothermic effects of morphine in examined animals. Implantation of morphine pellets caused the development of cross tolerance to ethanol-induced hypothermia in rats but not in mice. The hypnotic effect of ethanol was significantly shorter in chronic alcoholized rats but not in morphine-implanted rats. Neither chronic ethanol administration nor implantation of morphine pellets changed the duration of ethanol-induced hypnosis in mice. These results seem to support the hypothesis on the opiate-like mechanism of ethanol action.

The development of cross tolerance between ethanol and morphine.

The development of tolerance to ethanol-induced analgesia and cross tolerance between ethanol and morphine was studied in mice and rats. Chronic administration of ethanol resulted in the tolerance to its analgesic effects in rats (2.8 and 3.0 g/kg) as well as in mice (2.8 and 4.0 g/kg). Implantation of morphine pellets caused the development of cross tolerance to analgesic effect of 3.0 g/kg of ethanol in rats and 2.8 g/kg of ethanol in mice. The tolerance developed to antinociceptive effects of morphine (10 mg/kg) in chronic alcoholized mice but not in chronic alcoholized rats. These results seem to support the hypothesis on the opiate-like mechanism of ethanol action.

The influence of amphetamine and nomifensine on the development of morphine tolerance in the test of hypermotility in mice and catalepsy in rats.

The influence of drugs, which alter the brain catecholaminergic functions, on the development of morphine tolerance was studied. The experiments were carried out on mice in locomotor activity test, and on rats in catalepsy test. Tolerance to morphine was induced by subcutaneous implantation of morphine-base (37.5 mg) pellets. Amphetamine insignificantly diminished the development of tolerance to cataleptogenic effects of morphine in rats but markedly inhibited the development of tolerance to morphine-induced hyperactivity in mice. The latter action of amphetamine was blocked by pimozide. Administration of nomifensine induced the inhibition of the development of morphine tolerance in both tests. Pimozide also abolished this antagonistic action of nomifensine in locomotor activity test in mice. The obtained results have shown that intensification of dopaminergic neurotransmission induced the diminution of the development of tolerance to morphine.

Central action of narcotic analgesics. IX. Participation of serotonin in the development of tolerance to cataleptogenic effects of morphine in rats.

Subcutaneous implantation of morphine-base (75 mg) pellets over a period of 72 h caused the development of tolerance ot cataleptogenic action of morphine in rats. The development of morphine tolerance was inhibited by p-chlorophenylalanine (pCPA) or reserpine, drugs which decrease the content of brain serotonin (5-HT). Administration of 5-hydroxytryptophan (5-HTP(, which protected 5-HT stores against depleting action of reserpine, prevented the above of reserpine on the development of morphine tolerance in rats. Blockade of 5-HT neurotransmission by pizotifen or cyproheptadine inhibited the development of morphine tolerance, while the increase of it by imipramine did not alter the development of this tolerance . The Obtained results have shown that serotonergic system plays an important role in the development of tolerance to cataleptogenic effects of morphine.

Central action of narcotic analgesics. VII. The role of serotonin in the development of morphine tolerance in the locomotor activity test in mice and rats.

The development of tolerance to morphine-induced motor activity of mice and rats, as well as the influence of drugs which alter the brain serotonergic functions on the development of morphine tolerance was studied. Tolerance to morphine was induced by subcutaneous implantation of morphine-base pellets. After 72 h pellets were removed and 6 hr later motility was tested. Implantation of morphine pellets caused the development of tolerance to morphine-induced motor activity of mice and rats. Development of morphine tolerance was inhibited in mice and rats by p-chlorophenylalanine (pCPA) or reserpine, drugs which decrease content of brain serotonin. 5-hydroxytryptophan (5-HTP) inhibited the above effect of pCPA in mice, while tryptophan did not. Administration of 5-HTP, which protected serotonin stores against depleting action of reserpine decreased inhibiting action of reserpine on the development of morphine tolerance in rats. Although cyproheptadine and pizotifen did not alter the development of morphine tolerance in rats, nevertheless, it seems from these results that serotonin neurotransmission is of some importance in the development of tolerance to morphine.

Central action of narcotic analgesics. V. Participation of serotonin in the mechanism of action of narcotic analgesics.

The influence of serotonergic system on the changes in locomotor activity of mice and rats brought about by morphine, fentanyl, codeine and pentazocine and on morphine induced catalepsy in rats was studied. p-Chlorophenylalanine (pCPA) did not affect the behavioral changes produced in mice by morphine, fentanyl, codeine and pentazocine but reduced the behavioral depression produced by these drugs in rats. 5-Hydroxytryptophan (5-HTP) but not tryptophan (TP) reversed the action of pCPA on the effect of morphine and fentanyl. After reserpine the depression produced in rats by morphine and fentanyl was more pronounced. TP did not change the depression produced by combination of reserpine and morphine but counteracted the depression observed after combination of reserpine and fentanyl. In mice reserpine protected against hypermotility produced by morphine or fentanyl and TP potentiated the depression produced by the combination of reserpine and morphine or reserpine and fentanyl. Serotonin precursors, 5-HTP and TP evidently potentiated the morphine induced catalepsy. pCPA counteracted only the enhancement of the catalepsy observed after TP administration. Naloxone abolished the catalepsy after combined treatment with morphine and TP. Similarly but weaker acted cyproheptadine. The results suggest that the serotonin system plays a role in the effects of morphine and fentanyl on rat locomotor activity. An increase in the cerebral serotonin level increases the morphine catalepsy in rats.

Central action of narcotic analgesics. Part III. The role of endogenous noradrenaline in hyperactivity induced by morphine or fentanyl in mice.

Hyperactivity produced in mice with morphine or fentanyl, and methylamphetamine was antagonized by naloxone. The depression of locomotor activity induced by codeine was practically unchanged by the opiate antagonist. L-DOPA did not restore the stimulatory action of morphine and fentanyl in reserpinized mice. The hyperactivity produced by morphine and fentanyl was abolished in mice treated with alpha-methyl-p-tyrosine, but this was restored by L-DOPA administration. Agents inhibiting the central noradrenaline receptors, phentolamine, phenoxybenzamine, and aceperone, prevented or even reversed the locomotor stimulatory action of morphine and fentanyl. Pimozide did not affect the increase of locomotor activity produced by morphine, but depressed that induced by fentanyl. Haloperidol, used in a dose which did not affect the locomotor activity of mice, completely blocked or even reversed the stimulatory action of morphine and fentanyl, and potentiated the depression of locomotor activity produced by pentazocine and codeine. Diethyldithiocarbamate significantly depressed, but did not inhibit completely the stimulatory action of morphine and fetanyl. The stimulatory action of methylamphetamine was also significantly depressed. It seems that the stimulatory effect of morphine and fentanyl depends on the release of endogenous noradrenaline.

Central action of narcotic analgesics. II. Locomotor activity and narcotic analgesics.

The effect of morphine, codeine, fentanyl and pentazocine on locomotor activity of rats and mice and open-field performance of rats were tested. All the analgesics tested produced a depressive action in the rat. In mice a depressive action was produced by pentazocine and codeine. Fentanyl increased the exploratory and basal locomotor activity of mice. Morphine increased the exploratory activity, but, given at doses of 2.5 and 10 mg/kg decreased the basal locomotor activity. The increase of locomotor activity in mice by morphine and fentanyl is caused by an indirect stimulation of catecholamine receptors.

Central action of narcotic analgesics. I. Catalepsy and stereotypy in rats and narcotic analgesics.

The action of four analgesics, belonging to various pharmacological groups (morphine, codeine, fentanyl, pentazocine), was investigated in rats in tests for catalepsy and stereotypy, the tests depending on dopaminergic brain mechanisms. Interactions of the analgesics with a number of compounds known to affect dopaminergic brain functions in tests of catalepsy and stereotypy were also studied. In some experiments nalorphine, an antagonist of narcotic analgesics, was used. Morphine, codeine and fentanyl produced catalepsy, while pentazocine, at doses up to 60 microgram/kg, did not produce this effect. Reserpine, 2 mg/kg 3 hr before drugs, potentiated catalepsy produced by analgesics, while haloperidol, 0.2 mg/kg, 2 hr earlier, did not influence morphine and codeine catalepsy, but moderately potentiated fentanyl-induced catalepsy. alpha-methyl-p-tyrosine potentiated the cataleptogenic action of fentanyl and codeine, and also, less markedly, the action morphine. D-amphetamine (2.5-10 mg/kg) and apomorphine (5 mg/kg) moderately antagonized the catalepsy induced by analgesics, while atropine did not affect it. Nalorphine, 5 mg/kg, effectively abolished the catalepsy produced by narcotic analgesics, but did not affect that produced by neuroleptics. Morphine, codeine and fentanyl slightly inhibited apomorphine stereotypy, and evidently antagonized stereotypy produced by amphetamine. Pentazocine did not affect or slightly potentiated the both types of stereotypy. It is concluded that morphine, codeine and fentanyl, in contrast to pentazocine, inhibit behavioral activities depending on central dopaminergic functions in the rat. The mechanism of this action is most probably indirect, and seems to be related to the dopaminergic presynaptic functions.