Effects of enoxacin and its combination with 4-biphenylacetate, an active metabolite of fenbufen, on population spikes in rat hippocampal slices.

The effects of enoxacin, a new quinolone antibacterial agent, and its combination with 4-biphenylacetate (BPA), an active metabolite of the non-steroidal antiinflammatory agent fenbufen, were examined on population spikes induced by electrical stimulation of the stratum radiatum in the CA1 pyramidal cell layer in rat hippocampal slices. Enoxacin (10(-4) M) and bicuculline (10(-6) M) increased the amplitude of the population spikes and anew elicited the second spikes (latency: 10 msec.), while BPA (10(-5) M) decreased the amplitude of the population spikes. However, the combination of enoxacin (10(-6), 10(-5) M) with BPA (10(-5) M) elicited the second spikes or epileptiform bursts with an increase of the population spike amplitude. The dose-response relationships showed that the effect of enoxacin was 100 times potentiated in the presence of BPA (10(-5) M). The second spikes induced by enoxacin (10(-4) M) were suppressed by muscimol (10(-6) M) and baclofen (10(-6) M), but not by clorazepate (5 x 10(-5) M) and pentobarbital (5 x 10(-5) M). The second spikes induced by bicuculline (10(-6) M) were suppressed by these four drugs. The second spikes by the combination of enoxacin (10(-6) M) with BPA (10(-5) M) were suppressed by muscimol (5 x 10(-6) M), but not by clorazepate (5 x 10(-5) M). These results suggest that the combination of enoxacin with BPA exerts a drug interaction to elicit the second spikes or epileptiform bursts with its mode of action different from that of bicuculline.

Memory deficits following internal capsule lesions in rats and their improvement by L-6-ketopiperidine-2-carbonyl-L-leucyl-L-proline amide (RGH-2202), a thyrotropin-releasing hormone analogue.

A memory deficit model has been developed following bilateral internal capsule lesions in rats. During 12-49 days after internal capsule lesions, the rats showed a marked impairment of active avoidance acquisition in a step-through apparatus, while they exhibited no observable change in native behaviors, except a slight increase in exploratory activity. A passive avoidance task in the same apparatus was also impaired in internal capsule lesioned rats when examined after one-trial training, though the task was gradually acquired by repeated trainings. Moreover, the retention of both the active and passive avoidance responses in well-trained rats deteriorated after internal capsule lesions. On the other hand, internal capsule-lesioned rats did not perform any worse than sham-operated rats in a T-maze spontaneous alternation behavior and in a habituation response to a novel environment. In the frontal cortex and striatum of internal capsule-lesioned rats, there was a significant decrease of dopamine, serotonin and their metabolites, but no change of acetylcholine levels. The acquisition deficit of active avoidance in internal capsule-lesioned rats was improved by thyrotropin-releasing hormone (TRH, 10 mg/kg, i.p.) and L-6-ketopiperidine-2-carbonyl-L-leucyl-L-proline amide (RGH-2202, 10 mg/kg, i.p., 0.2 and 1 mg/kg i.v.), but not by physostigmine sulfate (0.2 mg/kg, i.p.). These results indicate that bilateral internal capsule lesions in rats induce long-term memory deficits which are paralleled with a decrease of the contents of monoamines and their metabolites and improved by TRH and RGH-2202.

[Analgesic activity of morphine suppository in rats].

Analgesic activity of morphine administered rectally as a suppository was investigated in rats in order to ascertain analgesic activity of morphine suppository. Morphine hydrochloride given rectally as a suppository produced analgesic activity in a dose-related manner in the tail pressure and acetic acid-induced writhing tests, and its potency (ED50 = about 17 and 0.689 mg/kg, respectively) was approximately twice that of morphine hydrochloride administered orally as an aqueous solution. The analgesic action was as durable as that of oral morphine, but its onset was faster. The plasma and brain levels of morphine reached peak until 30 min after rectal administration of morphine suppository, and these time-courses approximately corresponded with that of the analgesic action. These results suggest that morphine given rectally to rats as a suppository produces analgesic action equivalent or superior to orally administered morphine after absorption from the rectum.

L-6-ketopiperidine-2-carbonyl-L-leucyl-L-proline amide as a novel thyrotropin releasing hormone analogue with improving effects on impaired central nervous systems functions.

Psychopharmacological activities of L-6-ketopiperidine-2-carbonyl-L-leucyl-L-proline amide (RGH-2202) were compared with those of the parent peptide, thyrotropin releasing hormone (TRH, L-pyroglutamyl-L-histidyl-L-prolinamide, Pyr-His-Pro amide) in rodents. RGH-2202 caused qualitatively similar effects to TRH in a variety of tests for the activity on the central nervous system. The compound as well as TRH increased the spontaneous motor activity, enhanced the conditioned avoidance response, and antagonized the avoidance suppression by haloperidol and the sleep-inducing effect of pentorbarbital in mice. It was also efficacious against the deficits of consciousness in mice with concussive head injury and the EEG disturbance in rats with basilar artery occlusion. Besides, it antagonized the cycloheximide-or anoxia-induced amnesia and enhanced the habituation of exploratory activity in mice. Biochemically, it enhanced, like TRH, the turnover of norepinephrine and dopamine in the cerebral cortex, nucleus accumbens and striatum of mice and rats, and increased cyclic GMP levels in the cerebellum of rats. In spite of the global similarity between the pharmacological profiles of RGH-2202 and TRH, there were some intriguing differences between them. RGH-2202 was 2-5 times more effective than TRH in improving the deficits of active avoidance performance and retention in mice, while it was weaker than TRH in modifying the haloperidol-induced catalepsy in mice and enhancing the spinal reflexes in rats. Besides, its thyrotropin releasing activity was about 30 times less potent than that of TRH.(ABSTRACT TRUNCATED AT 250 WORDS)

Antihypertensive mechanism of alacepril. Effects of its metabolites on the peripheral sympathetic nervous system.

To elucidate the antihypertensive mechanisms of alacepril (DU-1219), the drug itself and its metabolites, desacetylalacepril (DU-1227) and captopril, were examined both in vitro and in vivo for their effects on the sympathetic nerve which innervates the peripheral vessels. 1. In isolated perfused mesenteric preparations from spontaneously hypertensive rats (SHR, DU-1227 (10(-6)-10(-5) mol/l) attenuated dose-dependently the increases in perfusion pressure and in norepinephrine (NE) overflow which were induced by electrical stimulation of periarterial sympathetic nerves (15 Hz). Captopril (10(-6)-10(-5) mol/l) caused a similar attenuation, though to a lesser degree, of the perfusion pressure but did not inhibit the increase in NE overflow. 2. The sympatho-inhibitory effect of DU-1227 in the above experiment was shown to be caused by DU-1227 per se, since no captopril was detected in either the perfusate or tissues perfused with DU-1227. 3. In pithed SHR, alacepril (3 mg/kg) caused as potent an inhibitory effect as captopril (3 mg/kg) on the pressor response to the electrical sympathetic nerve stimulation (3 Hz) at an oral dose about half as that of captopril on the molar basis. The effect of alacepril tended to last longer than that of captopril. However, at higher oral dose levels, the inhibitory effect of alacepril (30 mg/kg) was of the similar extent to that of captopril (30 mg/kg). 4. In pithed SHR which had received bilateral nephrectomy 2 to 8 h previously, alacepril (30 mg/kg p.o.) significantly attenuated the vasopressor response induced by electrical stimulation (1-30 Hz) 1 and 3 h after administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Physostigmine induces in rats a phenomenon resembling long-term potentiation.

The study dealt with a phenomenon similar to long-term potentiation of hippocampal population spikes that was observed with a high dose of physostigmine given to rats. The population spikes in the dentate granule cells in anesthetized rats were enhanced to 135, 152 and 167% of the control level 60, 120 and 240 min after the administration of physostigmine (0.1 mg/kg i.v.), respectively. The time course of the enhancement was consistent with that of blocked paired pulse inhibition by physostigmine in anesthetized rats. Such a block of paired pulse inhibition was seen at the observation of the long-term potentiation phenomenon to tetanic stimulation (100 Hz, 2 s). Perfusion of physostigmine (10(-5) M) or bicuculline (10(-6) M) elicited second spikes following the population spikes in CA1 pyramidal cells. The second spikes elicited by physostigmine were decreased by scopolamine (10(-6) M) and muscimol (5 x 10(-7) M), while those caused by bicuculline were decreased by muscimol but not by scopolamine. It is suggested that physostigmine induces a long-term potentiation-like phenomenon through a transient, abrupt increase in excitability and the subsequent block of recurrent GABAergic inhibition in the hippocampus.

Effect of metoclopramide and ranitidine on acetylcholine release from isolated rat stomach.

Metoclopramide and ranitidine (10(-6)-10(-4) M) enhanced the electrical field stimulation-evoked contractions of isolated rat fundus and increased the gastric emptying in conscious rats. The enhancement of the fundus contractions by metoclopramide and ranitidine was abolished by atropine, but not by yohimbine, hexamethonium, propranolol or methysergide. The electrical field stimulation-evoked [3H]outflow from rat fundus strips, which has been preincubated with [3H]choline, was reduced by tetrodotoxin (10(-6) M) or in calcium-free medium, and potentiated by 4-amino-pyridine (3 X 10(-4) M), an acetylcholine (ACh)-releasing agent. Metoclopramide and ranitidine (10(-6)-10(-4) M) did not increase the [3H]outflow from the strips, in spite of causing a significant enhancement of their contractile response. However, both agents caused an increase in the ratio of [3H]acetylcholine/[3H]choline released into the superfusate during electrical field-stimulation. In rat fundus homogenates, metoclopramide and ranitidine showed a significant cholinesterase inhibition. These results seem to cast a doubt on the generally held ACh release hypothesis for the action mechanism of metoclopramide on one hand, and suggest, on the other hand, that cholinesterase inhibition contributes to some extent to the gastrokinetic effects of metoclopramide and ranitidine.

Effects of physostigmine and scopolamine on long-term potentiation of hippocampal population spikes in rats.

To elucidate an involvement of the cholinergic system in the long-term potentiation phenomenon, effects of physostigmine and scopolamine on population spike and its long-term potentiation in the dentate granule cell layer of anesthetized rats and in the CA1 pyramidal cell layer of rat hippocampal slices were examined. In anesthetized rats, physostigmine (0.01 mg/kg, i.v.) enhanced at a late phase the long-term potentiation induced by tetanic stimulation (15 Hz, 15 s, 7.5 times the threshold for population spike) of the perforant path, while scopolamine (1.0 mg/kg) suppressed it at an early phase. The two drugs did not affect the population spike itself. The time course of the long-term potentiation under the treatment of physostigmine was similar to that induced by stronger tetanic stimulation (10 times the threshold). In hippocampal slices, physostigmine (10(-6)M) showed a tendency to enhance the long-term potentiation induced by tetanic stimulation (15 Hz, 15 s, 5 times the threshold) of the stratum radiatum, with an increase of the population spike itself. Scopolamine (10(-5)M) markedly suppressed the long-term potentiation with a decrease of the population spike itself. From these results, it is suggested that cholinergic modification by physostigmine or scopolamine affects the long-term potentiation phenomenon in the hippocampus under the in vivo and in vitro conditions.

Effect of OP-2507, a stable prostacyclin analogue on cerebral ischemia induced by unilateral ligation of common carotid artery in gerbils.

Effects of OP-2507 [15-cis-(4-propylcyclohexyl)-16,17,18,19,20-pentanor-9-deoxy -9 alpha-nitrilo- PGF1 methylester] on cerebral ischemia induced by unilateral ligation of common carotid artery in gerbils were investigated with reference to behavioral and neuropathological changes. A good coincidence between neurological symptoms and neuropathological changes was observed in gerbils after unilateral ligation of common carotid artery as revealed by the high percentage of coincidence (90% of total animals). All gerbils which showed neurological symptoms, either circling behavior or rolling fit, had cerebral infarction in their ipsilateral hemisphere. In these animals, neuropathological changes of cerebral regions were observed in cortex, corpus callosum, hippocampus, basal ganglia, interbrain and midbrain, in contrast with medulla oblongata and cerebellum which did not show any neuropathological changes. Pretreatment with a dose range of 1-30 micrograms/kg, s.c. of OP-2507 showed a protective effect in the occurrence of neurological symptoms, such as circling behavior and rolling fit, in a dose-dependent manner. The effect of OP-2507 was also confirmed in neuropathological examination which was performed with observation of neurological deficits in the same animals. The severity of cerebral infarction of all brain regions was significantly prevented by treatment with OP-2507. The results suggested that the protective effect of OP-2507 on regional infarction gave apparent protection against the occurrence of neurological deficits for this compound.

[Inhibitory effect of AD-1590, a non-steroidal anti-inflammatory drug, on allergic inflammation in mice and rats].

Effect of AD-1590 on allergic inflammations was investigated. AD-1590 and indomethacin at an oral dosage as high as 32 mg/kg did not show any significant inhibitory activity on rat passive cutaneous anaphylaxis, a type-I allergy, although prednisolone and cyproheptadine produced strong inhibition. Against rat adjuvant arthritis, type-III and -IV allergies, AD-1590 showed potent prophylactic (2 and 4 mg/kg/day) and therapeutic (0.4-1 mg/kg/day) effects when given orally once a day for 3 weeks beginning from just before and for 1 week starting from 14 to 18 days after adjuvant inoculation, respectively; however, its prophylactic and therapeutic potencies were about one-fourth and one-fifth, respectively, that of indomethacin. The arthritis was strongly inhibited with prophylactic treatment of prednisolone (1 mg/kg/day) or cyproheptadine (40 mg/kg/day). On the other hand, prednisolone (ED50 = 0.0119 mg/ear, topical) showed strong activity in inhibiting mouse contact hypersensitivity to oxazolone (ear edema), a type-IV allergy, but cyproheptadine only had weak activity. AD-1590 (0.318 mg/ear) and indomethacin (0.699 mg/ear) produced rather strong inhibition; in particular, AD-1590 produced almost complete inhibition at high dosages, whereas most of the non-steroidal anti-inflammatory drugs (NSAID) tested showed weak inhibition or a partial inhibition of about 50% even at the highest dosage. The oral potency of AD-1590 was about 2 and 100 times those of indomethacin and ibuprofen, respectively. These results demonstrate that in allergic inflammation, the pharmacological properties of AD-1590 are somewhat different from those of other NSAID and different from those of prednisolone and cyproheptadine.

Anti-inflammatory action of interleukin 1 through the pituitary-adrenal axis in rats.

The influence of lipopolysaccharide (LPS) and the endogenous pyrogens, recombinant human interleukin 1 (rHu-IL 1) and tumor necrosis factor (rHu-TNF), on acute inflammation was investigated in rats. LPS (0.3-3 micrograms/kg i.v.), rHu-IL 1 alpha (3-30 micrograms/kg), rHu-IL 1 beta (0.3-3 micrograms/kg) and rHu-TNF (3-30 micrograms/kg) inhibited the hind paw edema induced by carrageenan in a dose-related manner. The potency of rHu-IL 1 beta was 10 times or more than of rHu-IL 1 alpha. rHu-IL 1 alpha and rHu-TNF also inhibited the dextran-induced hind paw edema. Both types of rHu-IL 1 (0.001-10 ng/paw) neither inhibited nor enhanced the edema when given directly into the inflamed paw. rHu-IL 1 alpha did not show any significant anti-edema activity in adrenalectomized rats. The 3 cytokines tested caused a significant increase in the plasma levels of ACTH and corticosterone after i.v. administration; the potency of rHu-IL 1 beta was about 10 times that of rHu-IL 1 alpha. These results suggest that both rHu-IL 1 and rHu-TNF inhibit paw edema at least in part through pituitary-adrenal axis stimulation, and that rHu-IL 1 has no pro-inflammatory action in the paw edema induced by carrageenan in rats.

[A correlation between the species differences in anti-inflammatory activity of AD-1590, a non-steroidal anti-inflammatory drug, and its plasma level].

Authors have reported that the oral potency ratio of AD-1590 to indomethacin varies with the animal models employed; the ratio is 4, 2.3 and 31 in the tests of acetic acid-induced vascular permeability (male mice), carrageenan hind paw edema (male rats) and UV-erythema (female guinea pigs), respectively. Thus, the relationship between the difference in the anti-inflammatory activity of AD-1590 among animal models and the species difference of the plasma AD-1590 level was investigated in experimental animals in order to ascertain the cause of the difference in the potency ratio. Inhibitory potency of AD-1590 on UV-erythema and increased vascular permeability induced by acetic acid in male rats was about 2.1 and 2.3 times, respectively, that of indomethacin. On the other hand, after a single oral administration of 5 mg/kg, the highest plasma AD-1590 level was seen in female guinea pigs (AUC9-8 hr = 63.1 micrograms.hr/ml); and followed by that in mice (male, 32.1; female, 36.1) greater than male dogs (11.5) greater than or equal to rats (male, 9.02; female, 12.5), male rabbits (9.17) greater than male monkeys (9.34 at 6 mg/kg). Hucker et al. have reported that the plasma level of indomethacin in rats is several times higher than that in guinea pigs, rabbits and monkeys. These results suggest that most of the species difference in the relative potency of AD-1590 to indomethacin in the anti-inflammatory activity results from the species difference in the plasma level of both drugs.

Interleukin-1 induces analgesia in mice by a central action.

The effect of interleukin-1 together with lipopolysaccharide, tumor necrosis factor and interferon on a pain-like response was investigated with the phenylquinone-induced writhing test in mice. Recombinant human interleukin-1 alpha (rHu-IL-1 alpha) inhibited writhing dose relatedly at doses of 0.25-5 micrograms/kg i.v., and its potency was about 1000 times that of morphine on a molar basis. Potent anti-writhing activity was also seen after an i.v. dose of recombinant human tumor necrosis factor (rHu-TNF) and mouse alpha-interferon (mIFN alpha). Lipopolysaccharide, unlike rHu-IL-1 alpha, needed a lag time of about 1 h to develop its anti-writhing action. The relative potency ratios of intracisternal to i.v. and i.p. to i.v. administration of rHu-IL-1 alpha were about 38 and 0.1, respectively. The activity of rHu-IL-1 alpha and rHu-TNF, unlike mIFN alpha, was not naloxone-reversible. rHu-IL-1 alpha did not produce an increase in writhes counts even if injected directly into the peritoneal cavity. These results suggest that rHu-IL-1 alpha, as well as lipopolysaccharide, rHu-TNF and mIFN alpha, had potent anti-writhing activity when given i.v. and its action is due to a central mechanism but is not naloxone-reversible, and that rHu-IL-1 alpha is not algesic under the experimental conditions used.

Recombinant human tumor necrosis factor causes long-lasting and prostaglandin-mediated fever, with little tolerance, in rabbits.

The pyrogenic properties of high purified recombinant human tumor necrosis factor (rHu-TNF) were investigated in rabbits. rHu-TNF produced a clear biphasic fever reaching maximal values at 1 and 5 hr after bolus i.v. injections of 10 and 33 micrograms/kg; the initial febrile response was short-lasting, and not dose-related, but the second one was dose-related and lasted for 10 hr or more. The febrile response to rHu-TNF, unlike lipopolysaccharide, did not decrease after a single or two consecutive doses. A significant reduction in the febrile response, however, was seen after four consecutive doses starting from 7 days after the second dose; the febrile response 3 hr after rHu-TNF was much smaller, but the first peak was hardly smaller. Low anti-rHu-TNF levels were found in serum of rabbits treated repeatedly with rHu-TNF, suggesting that antibody production against rHu-TNF is not responsible for the tolerance formation although it may make some contribution. There was no cross-tolerance between rHu-TNF and lipopolysaccharide. On the other hand, the febrile response to rHu-TNF (33 micrograms/kg i.v.) was inhibited partially or completely blocked by i.v. administration of cyclooxygenase inhibitors or dexamethasone. rHu-TNF produced a marked increase in the cerebrospinal fluid prostaglandin E2 level after bolus i.v. injection. A significant level of rHu-TNF (1.6 and 6.4% of that in serum) was found in cerebrospinal fluid after bolus i.v. injection of 33 and 1000 micrograms/kg, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Antihypertensive activity of cadralazine in experimental hypertensive rats.

Antihypertensive and tachycardic activities of cadralazine were examined in experimental hypertensive rats (spontaneous, renal and deoxycorticosterone acetate-salt hypertension) after single or repeated oral administration, and compared with those of hydralazine. In single oral administration, cadralazine (0.3-5 mg/kg) produced a dose-related hypotensive effect and its maximum activity was equipotent to or more potent than that of hydralazine (1-5 mg/kg) in these hypertensive rats. The hypotensive effect of cadralazine appeared gradually and reached a maximum at 5-7 hr, while the maximum effect of hydralazine was observed at 1 hr after dosing. In SHR, the significant hypotensive effect of cadralazine persisted for 9-24 hr, but that of hydralazine lasted for only 1-12 hr. Therefore, there were marked differences in onset and duration of the hypotensive effect between cadralazine and hydralazine. Both drugs produced a dose-related tachycardic effect concomitant with the hypotensive effect. The separation ratios of cadralazine on these effects were equivalent to those of hydralazine. In repeated oral administration for 7 days, cadralazine (3 mg/kg/once a day) significantly reduced the daily starting blood pressure. The same response was obtained by 3 times daily repeated administration of hydralazine (3 mg/kg). Tolerance to the hypotensive and tachycardic effects was not observed during successive dosings of cadralazine or hydralazine. The potent and long lasting hypotensive effect of cadralazine might be useful for the treatment of arterial hypertension.

A possible role of endogenously formed cerebral prostaglandins in the development of adaptive protection against cerebral hypoxia/ischemia in mice.

We found recently that exogenously administered PGD2, PGE1 and PGI2 showed a protective effect against cerebral hypoxia/ischemia in mice. In the present study, to find out whether these PGs play a pathophysiological role in cerebral hypoxia/ischemia, we examined a possible role of PGs in the development of adaptive protection against cerebral hypoxia/ischemia. Mice were pretreated with a sublethal dose of KCN, hypoxic gas mixture and electroshock 10-120 min before tests. Ten to thirty min after pretreatment with a sublethal dose of KCN, mice proved to be significantly protected against cerebral hypoxia/anoxia in all models studied: KCN-induced anoxia, normobaric hypoxia and decapitation-induced gasping. Similar results were observed when hypoxic gas and electroshock were used as pretreatments. These facts indicate that the protective effect does not depend on how cerebral hypoxia/anoxia is induced but on the substances formed in the brain after hypoxia/anoxia as well as electroshock. Brain concentrations of cyclooxygenase products markedly increased subsequent to hypoxia/anoxia as well as electroshock. The increase in PGs formation as well as resistance to hypoxia was prevented by pretreatment with indomethacin. These findings suggest that endogenously formed PGs at least including the three PGs, PGD2, PGE1 and prostacyclin in mouse brain during or after hypoxia/ischemia are responsible for the increase of resistance to hypoxia/ischemia.