The effect of agonists at the GABA-benzodiazepine-receptor-complex on the proconflict effect induced by beta-CCM and pentetrazol in rats

The effect of anxiolytics, benzodiazepine (BZP), diazepam (DZP), non-BZP zopiclone (ZOP) and phenobarbital (PBT), on the proconflict effect induced by methyl-beta-carboline-3-carboxylate (beta-CCM) or by pentetrazol (PTZ) was investigated. The proconflict effect of beta-CCM and PTZ was reduced by these anxiolytics and aminooxyacetic acid (AOAA). In addition, isoniazid produced proconflict activity. Therefore, it is suggested that anxiolytics facilitate the GABA-ergic function, causing the inhibition of the proconflict effect. Although both propyl-beta-carboline-3-carboxylate (beta-CCP) and Ro15-1788 did not produce proconflict activity, they reduced the proconflict effect induced by beta-CCM but not by PTZ. These data clearly show that beta-CCM exerts the proconflict effect through interaction with BZP receptor and that there are behavioral similarities between beta-CCP and Ro15-1788. In this study, we additionally observed the time latency until the rat began to drink the water. beta-CCM and PTZ prolonged this latency in a dose-dependent manner. However, AOAA could not reduce the prolonged latency induced by beta-CCM and by PTZ, and anxiolytics and beta-CCP could not reduce the prolonged latency induced by beta-CCM. The mechanism of the prolongation of latency induced by beta-CCM and PTZ seems to be different from that of the proconflict effect.

Inhibitory effect of apomorphine on hippocampal stimulation-induced "wet-dog shakes" in rats may be due to a stereotyped behavior

The effect of apomorphine on "wet-dog shakes" (WDS) elicited by hippocampal stimulation was investigated. Apomorphine in doses of 1.0 and 2.0 mg/kg given to rats s.c. reduced the number of WDS. Haloperidol in doses of 0.2-1.0 mg/kg given i.p. also significantly and dose-dependently reduced the number of WDS. The inhibitory effect of apomorphine in doses of 1.0 and 2.0 mg/kg on WDS was completely inhibited by haloperidol given in a dose of 0.5 mg/kg. It is, therefore, conceivable that the inhibition of WDS produced by apomorphine in doses of 1.0 and 2.0 mg/kg may result from the occurrence of stereotyped behavior and that the dopaminergic blocking action may be crucial for the inhibition of WDS induced by hippocampal stimulation. Despite a 50% increase in stimulation intensity, as compared with the afterdischarge threshold, the number of WDS remained unchanged. We tentatively concluded that apomorphine fails to increase the number of WDS, as a result of the ceiling phenomenon.

Involvement of the medial amygdaloid nucleus in the action of imipramine in rats subjected to the forced swimming test

A forced swimming test proposed by Porsolt is a useful method for screening antidepressants. To evaluate drug effects more objectively, vibration of the walls of a water tank caused by the escape behavior of the rat was recorded. Imipramine (IMI) increased the number of vibration and this effect was observed in the medial amygdala lesioned rat but not in the central or basolateral amygdala lesioned rat. The present result suggests that the medial amygdala is an important site of action of IMI.

Gastric motility is an important factor in the pathogenesis of indomethacin-induced gastric mucosal lesions in rats

Effects of atropine, cimetidine, and 16,16-dimethyl prostaglandin E2 (16,16-dmPGE2) on indomethacin-induced gastric lesions were investigated in rats by correlating their effects on gastric acid and HCO3- secretion and motility. Subcutaneously administered indomethacin (25 mg/kg) produced gastric mucosal lesions within 4 hr. In parallel studies, an equivalent dose of indomethacin inhibited gastric HCO3- secretion, and stimulated gastric motor activity measured as intraluminal pressure recordings, whereas acid secretion was unaffected. The lesions induced by indomethacin were significantly prevented by three agents: cimetidine (100 mg/kg), which reduced acid secretion; atropine (1 mg/kg), which reduced acid secretion and gastric motility; and 16,16-dmPGE2 (10 micrograms/kg), which reduced acid secretion and motility and increased gastric HCO3- secretion. If acid (150 mM HCl) was infused into the stomach (1.2 ml/hr) during indomethacin treatment, only the latter two agents significantly prevented the formation of gastric lesions in response to indomethacin. Since only the effect on gastric motility was common to these two agents (atropine and 16,16-dmPGE2), the increased gastric motility may be an important pathogenetic factor in indomethacin-induced gastric lesions. The presence of acid as well as a deficiency of endogenous PGs may be prerequisite for later extension of the lesions but cannot account for the induction of mucosal lesions in rats following administration of indomethacin.

Anti-serotonin action in combination with noradrenaline-stimulating action is important for inhibiting muricide in midbrain raphe-lesioned rats

The present study was designed to examine the possible involvement of both an anti-serotonin action and a catecholamine-stimulating action in the mechanism of the inhibition of the muricide in rats with lesions of the midbrain raphe. Serotonin antagonists, such as cyproheptadine (10 mg/kg), cinanserin (10 mg/kg) and pirenperone (1 mg/kg), given alone showed little suppression of muricide in rats with raphe lesions, although the first two drugs were inhibitory at very large doses. Methamphetamine showed no inhibition of muricide at 0.32 mg/kg (i.p.), but exerted a marked inhibition of muricide when combined with the above serotonin antagonists. In addition, the dose-response curve for cyproheptadine and cinanserin was shifted markedly to the left when combined with L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS) (100 mg/kg i.p.), but not with lisuride (0.32 mg/kg i.p.). Similarly, pirenperone produced a marked inhibition of muricide at doses of 0.32-1.8 mg/kg (i.p.) when combined with L-threo-DOPS, but not when combined with lisuride. These results suggest that the combination of an anti-serotonin action with noradrenergic activation is important for inhibiting muricide, at least in rats with raphe lesions. A similar mechanism also seems to be valid for the anti-muricidal effect of antidepressant drugs.

A new method for studying working memory by using the three-panel runway apparatus in rats

We designed a new method for studying working memory, by using a repeated acquisition procedure in the three-panel runway apparatus. This apparatus is composed of a start box, a goal box and four consecutive choice points; each choice point consists of three panel gates. Male Wistar rats were trained with 6 consecutive trials (one session) per day. Each trial was performed every two minutes. In this apparatus, rats could pass through only one gate (correct gate) among three panel gates in the direction of the goal box and were given 100 mg food pellets as the positive reinforcement. The sequence of correct gate position in each rat was changed everyday, but not in each session. Error responses (pushing the incorrect gate) were gradually reduced as training was repeated, and the learning was established within 16 training sessions to achieve criterion performance. Intraperitoneal scopolamine and intrahippocampal ethylcholine aziridinium ion (AF64A) produced increases in both the number of errors and the latency in a dose-dependent manner. The increase in errors induced by AF64A did not return to the control level, though the prolonged latency returned to normal. As a conclusion, this experimental procedure using the three-panel runway apparatus would be a useful method for studying working memory, and its memory deficit is involved at least in the dysfunction of the cholinergic system in the hippocampus.

Enhancement by alpha-fluoromethylhistidine of the thiopental sleep-prolonging action of delta 9-tetrahydrocannabinol

The effect of alpha-fluoromethylhistidine (alpha-FMH), a specific inhibitor of histidine decarboxylase, on the potentiation of thiopental-induced sleep by delta 9-tetrahydrocannabinol (THC), which inhibits the histamine turnover in the brain, was examined in mice and rats. The sleeping time after injection of thiopental sodium (40 mg/kg, IV) was prolonged by THC (10 mg/kg, IP, 1 h before) to approximately twice the control value. alpha-FMH (50 mg/kg, IP) administered alone had no significant influence on the thiopental sleeping time. However, alpha-FMH given 1 or 3 h before THC treatment markedly enhanced the THC potentiation of thiopental-induced sleep. Such an enhancement by alpha-FMH was not observed when alpha-FMH was administered 15 h before THC treatment. The brain histamine level decreased by 60% during the first 4 h after alpha-FMH injection and remained low until 15 h after the treatment. The thiopental sleep-potentiating action of morphine, chlorpromazine and diazepam was not affected by pretreatment with alpha-FMH. The transient enhancing effect of alpha-FMH on the THC potentiation of thiopental-induced sleep suggests that the histaminergic system is one of the activating transmitter systems in the brain.

A new forced swimming test for the evaluation of antidepressants in rats by recording vibration of a water tank

In order to more objectively evaluate drug effects in the forced swimming test proposed by Porsolt et al. as a screening method for antidepressants, vibrations of the wall of a tank caused by rats trying to escape from water were recorded. Locomotor activity was also measured in an activity cage. Male Wistar rats were forced to swim once daily for 15 min in a tank of 25 degrees C water filled to a depth of 20 cm. After 4 d sessions of swimming, drugs were administered i.p. 3 times (24, 5 and 1 h prior to the test session). On day 5, 45 min after the last injection of a test drug, locomotor activity was measured for 15 min and then the rat was subjected to the forced swimming test. All antidepressants tested, dose-dependently increased tank vibration. Nomifensine, atropine, methamphetamine, chlorpheniramine and diazepam increased locomotor activity. The remaining drugs had no effect or reduced locomotion. In addition, the pattern of the tank vibrations, caused by rats treated with most drugs, like atropine, showed a burst during the first 5 min followed by sporadic vibrations. Nomifensine and methamphetamine, on the other hand, caused vibrations throughout the 15 min test session. A specific effect of antidepressants was revealed by this forced swimming test in combination with the measurement of locomotor activity.

The effect of agonists at the GABA-benzodiazepine receptor complex on the duration of immobility of mice in the forced swimming test

In the present study, we examined the effect of various agents which affect in a different manner the GABA-benzodiazepine receptor-chloride ionophore complex system in relation to the immobile behavior of mice in the forced swimming test. The benzodiazepines diazepam and flurazepam, the barbiturates pentobarbital and phenobarbital, zopiclone and beta-CCP (propyl-beta-carboline-3-carboxylate) enhanced the immobile behavior in a dose-dependent manner. In the doses used here, these agents produced almost no muscle relaxant action. Ro15-1788 and beta-CCM (methyl-beta-carboline-3-carboxylate) themselves had no effect on the duration of immobility. However, Ro15-1788 and beta-CCM reversed the enhancing effect produced by all 6 drugs. These results indicate that the enhancement of the duration of immobility of mice may be somehow correlated to the anxiolytic action but not to the muscle relaxant action. The effect may be mainly mediated by the benzodiazepine receptor, which forms a part of the GABA-benzodiazepine receptor-chloride ionophore complex. Furthermore it is suggested that there were behavioral similarities in the effects of beta-CCP and benzodiazepines.

The involvement of neuropeptide Y in the antimuricide action of noradrenaline injected into the medial amygdala of olfactory bulbectomized rats

The present study was designed to clarify the functional role of neuropeptide Y (NPY) in the regulation of muricide induced by olfactory bulbectomy (OB) in relation to that of noradrenaline (NA) in the medial amygdala (AME). NA injected into AME inhibited muricide dose-dependently in OB rats. NPY at doses of 5 and 10 micrograms/microliter injected alone into AME failed to suppress muricide. When NPY 10 micrograms was injected into AME in combination with the maximal non-effective dose of NA, which was determined in each rat, muricide was suppressed in 80% of OB rats. The present study has provided the first evidence suggesting that NPY may be involved in the regulation of OB-induced muricide.

Differential mechanisms involved in the anticonflict action of benzodiazepines injected into the central amygdala and mammillary body

The present study was designed to clarify the mechanism of action of benzodiazepines (BDZ) injected into the central amygdala (ACE) and mammillary body (MB). When gamma-aminobutyric acid (GABA) at doses of 30 and 70 micrograms, muscimol (0.01 and 0.03 microgram), valproate (200 micrograms), atropine (20 micrograms) and cyproheptadine (3 micrograms) were bilaterally injected into ACE, a significant and marked increase in the punished responses of conflict schedule was observed. These drugs injected into MB failed to increase the punished responses. In MB, only noradrenaline (NA, 20 micrograms) showed the anticonflict action. NA 20 micrograms also produced the anticonflict action in ACE. These results suggest that the mechanism of anticonflict action of BDZ is different in brain areas. The GABA-ergic, cholinergic, serotonergic and NA-ergic systems seem to be involved in the mechanism of anticonflict action of BDZ in ACE. While the NA-ergic system appears to be operative in MB.

Influences of electrical lesions of the dopaminergic system on morphine- and U-50,488H-induced analgesia in rats

The effects of electrical lesions of brain areas containing dopamine cell bodies and terminals on morphine analgesia were investigated and compared with those of a selective kappa-opioid agonist, U-50,488H. The analgesic effect of morphine 10 mg/kg IP was potentiated significantly in substantia nigra (SN)- or caudate-putamen-lesioned rats, but not by ventral tegmental area (VTA) or nucleus accumbens lesions. However, electrical lesions of neither SN nor VTA affected the analgesic activity of U-50,488H 32 mg/kg IP. Although the tolerance to morphine analgesia developed in all four of the lesioned groups as well as in sham-lesioned rats, a significant analgesic effect in the SN-lesioned group prevailed during chronic treatment for 14 days as compared with that of sham-lesioned rats. From these results, it is suggested that morphine analgesia is potentiated by dysfunction of the nigro-striatal dopaminergic system, but not by that of the mesolimbic dopaminergic system, the central dopaminergic system is not involved in the appearance of U-50,488H analgesia and is not basically related to the development of tolerance to morphine analgesia.

Clonidine attenuates wet-dog shaking induced by hippocampal stimulation in rats

The effect of an alpha 2-adrenoceptor agonist, clonidine on wet-dog shaking (WDS; also, WDS = wet-dog shakes) induced by electrical stimulation of the hippocampus was investigated. Clonidine (0.01-0.32 mg/kg i.p.) inhibited the appearance of WDS in a dose-dependent manner without showing any effect on hippocampal afterdischarge. Although clonidine has been reported to inhibit the activity not only of noradrenergic but also of serotonergic neurons, a 5-hydroxytryptamine (5-HT) antagonist, cinanserin at doses up to 32 mg/kg had no significant effect on hippocampal stimulation-induced WDS. Therefore, a possible anti-5-HT action of clonidine in the inhibition of WDS can be excluded. The WDS inhibition produced by clonidine was blocked significantly by pretreatment of the rats with an alpha 2-adrenoceptor antagonist, yohimbine, but not with a narcotic antagonist, naloxone. The present results suggest that a central noradrenergic function may be involved in WDS induced by hippocampal stimulation.

Behavioral pharmacology of zopiclone

The pharmacological properties of zopiclone, a cyclopyrrolone derivative, have been studied in comparison with diazepam, nitrazepam, and flurazepam, on behavioral tests in mice and rats, including open-field activity, Skinner box conflict test, hyperemotionality and muricidal behavior of olfactory bulbectomized or raphectomized rats, pentetrazol or electroshock convulsions, inclined screen, rotarod, and thiopental-, ether-, or ethanol-induced anesthesia. Zopiclone exhibited pharmacological properties qualitatively similar to those of benzodiazepines especially in conflict, aggressivity, and pentetrazol-induced convulsion tests. On the other hand, its myorelaxant activity was somewhat weaker than that of the reference drugs. The pharmacological effects of zopiclone were of short duration.

Changes of brain monoamine contents in three models of experimentally induced muricide in rats

Monoamine levels were measured by high performance liquid chromatography with electrochemical detection in seven brain regions of three models of experimentally-induced muricide (mouse-killing behavior) in rats (bilateral olfactory bulbectomized rats: OB rats, midbrain raphe nuclei lesioned rats: Raphe rats and nucleus accumbens lesioned rats: Acc rats). Noradrenaline (NA) levels in the lateral hypothalamus (LH) and ventromedial hypothalamus (VMH), 3,4-dihydroxyphenylacetic acid (DOPAC) levels in LH and homovanillic acid (HVA) levels in the frontal cortex (FC) were increased in all three muricide models. In LH, serotonin (5-HT) levels increased in Acc rats and the 5-hydroxyindoleacetic acid (5-HIAA)/5-HT ratio was reduced in OB rats. But in VMH an increase in NA level was not accompanied by any changes of other amines in three muricide models except for 5-HT and 5-HIAA in Raphe rats. In the mamillary body (MB), NA level was increased and 5-HIAA/5-HT ratio was decreased in both OB and Acc rats. Monoamine changes in the amygdaloid nuclei were different in three muricide models, suggesting that the role of monoamines in various nuclei of the amygdala may be different in each muricide model. The present findings suggest that both noradrenergic (LH and VMH) and serotonergic function (LH and MB) may play an important role in exhibiting muricide of OB, Raphe and Acc rats, while dopaminergic function (LH and FC) may be related rather to hyperirritability elicited in these three muricide models.

Behavioral and electroencephalographic effects of zopiclone, a cyclopyrrolone derivative

Behavioral effects of zopiclone were investigated in mice and rats and compared with the data on diazepam, nitrazepam and flurazepam. The electroencephalographic effect of the drug was also examined in unanesthetized rabbits with chronic electrode implants and compared with that of diazepam. The present results indicate that zopiclone possesses pharmacological properties qualitatively similar to benzodiazepines, which are characterized by potent anticonflict and antiaggressive effects and much weaker anticonvulsant, muscle relaxant, ataxiogenic, sedative and anesthesia potentiating effects; the properties of this drug were compared with those of diazepam, nitrazepam and flurazepam. Zopiclone suppressed the EEG arousal responses and inhibited afterdischarges induced by electrical stimulation of the hippocampus and amygdala. The effects of zopiclone on EEG and afterdischarges were approximately 1/10 those of diazepam.

The role of brain catecholamines in the exhibition of muricide induced by nucleus accumbens lesions and the effect of antidepressants in rats

Changes in brain catecholamine content after lesioning the nucleus accumbens (ACC) and the effects of antidepressants were investigated using HPLC-ECD. ACC lesion reduced dopamine (DA) in the rostral caudate-putamen (r-CP), lateral hypothalamus (LH) and central amygdala (ACE). Imipramine (IMP) and nomifensine (NOM) increased DA in r-CP, caudal (c)-CP and basolateral amygdala. Mianserin (MIAN) and zimelidine (ZIM) increased DA only in c-CP. ACC lesion did not change DOPAC. Only IMP (in c-CP) and NOM (in r-CP and c-CP) increased DOPAC. Noradrenaline (NA) was decreased in c-CP and ACE after ACC lesion. IMP and ZIM displayed no effect on NA, while NOM increased NA in LH and frontal cortex (FC) and MIAN only in FC. These results suggest an important role for DA but not NA in the exhibition of muricide after ACC lesion, and in the antimuricide effect of antidepressants.

Rolipram as a discriminative stimuli: transfer to phosphodiesterase inhibitors

Rats were trained to discriminate (+/-)-rolipram (0.32 mg/kg, i.p.) from saline in a two-lever food-reinforced drug discrimination procedure (FR 10). (+/-)-Rolipram served as a drug discriminative stimulus, and its discrimination was readily established with a mean of 42 training sessions to achieve criterion performance (at least 80% correct response in the consecutive generalization tests with both saline and (+/-)-rolipram). Thereafter, this stimulus was stably maintained. The (-)-isomer of rolipram was generalized at about one-third of the training dose of the (+/-)-compound, but the (+)-isomer was generalized only at 10 times the dose of the (+/-)-compound. This finding suggests that the (-)-compound is more extensively involved as a stimulus than either (+/-)-rolipram or the (+)-isomer. Ro20-1724, caffeine and theophylline, which are phosphodiesterase inhibitors, were generalized to (+/-)-rolipram. This result strongly suggests that phosphodiesterase inhibition may be an important factor involved in (+/-)-rolipram discrimination.

A new method for screening anxiolytic drugs in rats

In order to evaluate the anxiolytic action of drugs, a simple experimental procedure using a corridor-type runway was designed. In this apparatus, five food pellets were set in a row on a plastic platform. Rats with one day food-deprivation take a food pellet and then usually return to the start box. The time required to take 5 pellets (total time) and the number of returns were recorded. Diazepam (DZP) at 1-3.2 mg/kg and zopiclone (ZOP) at 10 mg/kg caused decreases in both parameters. These effects were blocked by the benzodiazepine receptor blocker, Ro15-1788, at 10 mg/kg. However, tracazolate failed to produce any change in both parameters. Haloperidol and imipramine prolonged the total time while reducing the number of returns. In contrast to DZP and ZOP, pentetrazol, well known to possess an anxiogenic effect, prolonged the total time. These results suggest that decreases in both the total time and the number of returns produced by DZP and ZOP may be related to their anxiolytic action which is mediated by a benzodiazepine receptor. Therefore, this procedure would be a simple and selective method for detecting benzodiazepine-type anxiolytics.

The effect of kappa-opioid agonist U-50, 488H on wet-dog shaking behavior induced by hippocampal stimulation in rats

The effect of a selective kappa-opioid agonist, U-50, 488H, on wet-dog shaking (WDS) induced by hippocampal stimulation was investigated and compared with that produced by morphine. U-50, 488H, as well as morphine, inhibited the appearance of WDS in a dose-dependent manner. U-50, 488H was approximately three times more potent than morphine in this effect. Neither drug showed any effect on hippocampal afterdischarge. The inhibition of WDS produced by U-50, 488H was blocked significantly by a kappa-opioid antagonist, MR-2266, but not by naloxone. On the other hand, the inhibitory effect of morphine was completely antagonized by both MR-2266 and naloxone. The present results strongly suggest that not only mu-but also kappa-opioid receptors are involved in the appearance of WDS induced by hippocampal stimulation.

Noradrenergic involvement in catalepsy induced by delta 9-tetrahydrocannabinol

In order to elucidate the role of the catecholaminergic system in the cataleptogenic effect of delta 9-tetrahydrocannabinol (THC), the effect of pretreatment with 6-hydroxydopamine (6-OHDA) or with desipramine and 6-OHDA and lesions of the locus coeruleus were investigated in rats. The cataleptogenic effect of THC was significantly reduced in rats treated with 6-OHDA and in rats with lesions of the locus coeruleus but not in rats treated with desipramine and 6-OHDA, as compared with control rats. On the contrary, the cataleptogenic effect of haloperidol was significantly reduced in rats treated with desipramine and 6-OHDA but not in rats treated with 6-OHDA or in rats with lesions of the locus coeruleus. These results indicate that noradrenergic neurons have an important role in the manifestation of catalepsy induced by THC, whereas dopaminergic neurons are important in catalepsy induced by haloperidol.

Effects of indomethacin on the duodenal mucosa of rats: comparative study with cysteamine

Effects of indomethacin and cysteamine on the duodenal mucosa of rats were studied microscopically (using scanning electron microscopy) and also functionally. Indomethacin (5 mg/kg, s.c.) induced no microscopic damage to the duodenal epithelium for up to 6 hr after administration. Indomethacin had no effects on gastric H+ output and the amount of H+ in the duodenum, but did reduce the duodenal HCO3- secretion (both basal and 10 mM-HCl stimulated). PGE2 contents in the duodenal mucosa were markedly reduced by indomethacin for 6 hr. These results suggest that reductions of duodenal HCO3- secretion and endogenous prostaglandins per se do not impair the H+ disposal system of the duodenum and so do not damage the epithelial cells. In contrast, cysteamine (100 mg/kg, s.c.) produced microscopic damage to the duodenal epithelium as early as 2 hr later. Cysteamine significantly increased gastric H+ output and reduced duodenal HCO3- secretion, resulting in an increased amount of H+ in the duodenum 3 hr later. Cysteamine had no effect on PGE2 contents in the duodenum. The time lag between damage formation and functional changes suggests that the earliest damage caused by cysteamine occurs by mechanisms other than erosive action of H+ emptied by the stomach. The increased amount of H+ may contribute to an enhancement of the initial damage.

Pathogenic mechanisms involved in mepirizole-induced duodenal damage in the rat

Mepirizole (60 and 200 mg/kg) administered s.c. induced damage in the surface epithelial cells of the rat proximal duodenum as early as 2 hr after the treatment. 16,16-Dimethyl prostaglandin E2 (dmPGE2, 30 micrograms/kg) administered s.c. significantly protected the duodenal mucosa against mepirizole-induced damage for up to 6 hr. Gastric acid secretion in acute fistula preparations was significantly reduced 1 hr after administration of mepirizole (60 and 200 mg/kg). The secretion reverted to the control level 2 hr later. In the 60 mg/kg-treated group, however, there was a significant increase in the acid output for up to 6 hr. Duodenal HCO3- secretion, stimulated with 10 mM HCl was significantly inhibited with mepirizole (60 and 200 mg/kg). Mepirizole (60 and 200 mg/kg) significantly increased the amount of acid in the duodenum for 2 to 6 hr after the treatment. dmPGE2 (30 micrograms/kg) significantly inhibited gastric acid secretion, stimulated duodenal HCO3- secretion, and reduced the increased amount of acid in the duodenum in response to mepirizole. Endogenous prostaglandin E2 and 6-keto prostaglandin F1 alpha in the duodenal mucosa were significantly reduced by mepirizole (200 mg/kg) 1 to 2 hr later. Mepirizole-induced duodenal damage appears to be caused by the increased amount of acid in the duodenum.

Importance of gastric motility in the pathogenesis of indomethacin-induced gastric lesions in rats

Effects of indomethacin on gastric motility and secretion, and levels of endogenous prostaglandins (PGs) were investigated in rats, in attempts to elucidate the factors involved in the pathogenesis of indomethacin-induced macroscopic gastric lesions. Subcutaneous administration of indomethacin had no effect on the gastric mucosa at doses of 1 and 5 mg/kg, but induced visible lesions dose dependently at over 10 mg/kg within 4 hr. At 25 mg/kg, there were apparent nonhemorrhagic lesions within 1 hr, and these lesions became hemorrhagic with time. Acid secretion was not affected by this agent at either dose level, but pepsin or acid-induced HCO3- secretion was significantly increased or decreased, respectively, at a dose less than 5 mg/kg, which did not induce any lesion. Gastric motility, however, was dose dependently increased after administration of indomethacin, and its effect was significant at 10 mg/kg or greater. Time-course changes in the motility were in parallel with those of the lesion formation. PGE2 and 6-keto PGF1 alpha levels in the corpus mucosa were reduced around 80-90% for more than 4 hr from 30 min after administration of 5 mg/kg or more of indomethacin. When all the above changes caused by indomethacin were plotted for the various doses, a significant correlation (r = 0.958, P less than 0.01) was found between the lesion index and the changes in motility, but not in other factors, including PG levels. These results indicate that gastric motility may be an important factor in the pathogenetic mechanism of indomethacin-induced gastric lesions in rats. A deficiency of endogenous PGs may be a prerequisite for later extension of the lesions.