Tetrandrine, a bisbenzylisoquinoline alkaloid from Chinese herb Radix, augmented the hypnotic effect of pentobarbital through serotonergic system

This is the first study of hypnotic activity of tetrandrine (a major component of Stephania tetrandrae) in mice by using synergism with pentobarbital as an index for the hypnotic effect. The results showed that tetrandrine potentiated pentobarbital (45 mg/kg, i.p.)-induced hypnosis significantly by reducing sleep latency and increasing sleeping time in a dose-dependent manner, and this effect was potentiated by 5-hydroxytryptophan (5-HTP). In the subhypnotic dosage of pentobarbital (28 mg/kg, i.p.)-treated mice, tetrandrine (60 and 30 mg/kg, p.o.) significantly increased the rate of sleep onset and also showed synergic effect with 5-HTP. Pretreatment of p-chlorophenylalanine (PCPA, 300 mg/kg, s.c.), an inhibitor of tryptophan hydroxylase, significantly decreased pentobarbital-induced sleeping time and tetrandrine abolished this effect. From these results, it should be presumed that serotonergic system may be involved in the augmentative effect of tetrandrine on pentobarbital-induced sleep.     

Yokukansan Enhances Pentobarbital-Induced Sleep in Socially Isolated Mice: Possible Involvement of GABA(A) - Benzodiazepine Receptor Complex

In the present study, we investigated the effect of the Kampo medicine Yokukansan (YKS) on pentobarbital-induced sleep in group-housed and socially isolated mice. Socially isolated mice showed shorter sleeping time than the group-housed mice. YKS (300 mg/kg, p.o.) prolonged the pentobarbital-induced sleeping time in socially isolated mice without affecting pentobarbital sleep in group-housed mice. The prolongation of sleeping time by YKS was reversed by bicuculline (3 mg/kg, i.p.) and flumazenil (3 mg/kg, i.p.), but not WAY100635. These findings suggest that the GABA(A)-benzodiazepine receptor complex, but not 5-HT(1A) receptors, is involved in the reversal effect of YKS on the decrease of pentobarbital sleep by social isolation.     

Morphine analgesia and the bulbospinal noradrenergic system: Increase in the concentration of normetanephrine in the spinal cord of the rat caused by analgesics

1 Administration of an analgesic dose (10 mg/kg, s.c.) of morphine increased the concentration of a noradrenaline metabolite, normetanephrine (NM) in the spinal cord of normal rats. The time course of the change in the NM concentration corresponded approximately to that of the morphine analgesia. The concentration of noradrenaline was not affected.2 A similar effect on the NM concentration was also observed after the administration of pentazocine (30 mg/kg, s.c.) and nalorphine (20 mg/kg, s.c.).3 The NM increasing effect of morphine, pentazocine and nalorphine was found in the dorsal half of the spinal cord but not in the ventral half.4 The increase in the concentration of NM induced by morphine, pentazocine or nalorphine was completely suppressed by naloxone (1 mg/kg, s.c.) given 5 min before the administration of these drugs.5 When the spinal cord was transected at C1, the NM increasing effect of morphine disappeared, yet when the brain stem was transected at the inter-collicular level, the effect remained.6 In morphine-tolerant rats, the concentration of NM in the spinal cord was almost the same as that observed in normal rats, but the increase in the concentration of NM in the spinal cord after the acute administration of morphine did not take place.7 The NM concentration in the spinal cord of normal rats was not modified by aminopyrine (75 mg/kg, s.c.), chlorpromazine (10 mg/kg, s.c.), mephenesin (100 mg/kg, i.p.) or naloxone (25 mg/kg, s.c.).8 The possible relation between morphine analgesia and the descending noradrenergic neurones in the spinal cord of rats is discussed.     

Ketamine-induced potentiation of morphine analgesia in rat tail-flick test: role of opioid-, alpha2-adrenoceptors and ATP-sensitive potassium channels

Ketamine is known to improve opioid efficacy, reduce postoperative opioid requirement and oppose opioid associated pain hypersensitivity and tolerance. However, the mechanisms underlying these beneficial effects are not clear. This study investigated the effects of ketamine at a non-analgesic dose (30 mg/kg, i.p.) on analgesia induced by morphine (2.5, 5.0, 7.5 mg/kg, s.c.), using rat tail-flick test as an animal model of acute pain. Further, the role of opioid-, alpha2-adrenoceptors and ATP-sensitive potassium channels was examined on the potentiating effect of ketamine. Male rats received morphine alone at 5.0 and 7.5 but not at 2.5 mg/kg showed a dose-related increase in tail-flick latencies. The combination of morphine and ketamine resulted in dose-related increase in morphine analgesia, both on the intensity as well as on duration. The ketamine-induced potentiation of morphine (7.5 mg/kg) analgesia was unaffected by glibenclamide (3 mg/kg, s.c.) and only partially blocked by yohimbine (2 mg/kg, i.p.), but more completely abolished by naloxone (2 mg/kg, i.p.). Both morphine (5.0 mg/kg) and ketamine (30 mg/kg) alone did not evoke catalepsy in rats but on combination produced a synergistic effect, which was however, abolished by naloxone pretreatment. In the open-field test, while morphine (5.0 mg/kg) caused a depressant effect, ketamine (30 mg/kg) enhanced the locomotor activity. Nevertheless, in combination potentiated the morphine's depressant effect on locomotion, which was also antagonized by naloxone. These results indicate that ketamine at a non-analgesic dose can potentiate morphine analgesia, induce catalepsy and cause locomotor depression, possibly involving an opioid mechanism. This potentiation, although favorable in acute pain management, may have some adverse clinical implications.     

Spinosin, a C-glycoside flavonoid from semen Zizhiphi Spinozae, potentiated pentobarbital-induced sleep via the serotonergic system

Semen Zizhiphi Spinozae has been used extensively for the treatment of insomnia. This study investigated the effect and possible mechanism of action of spinosin (also known as 2'-beta-o-glucopyranosyl swertisin), a major constituent of semen Zizhiphi Spinozae, on sleep in mice. The present results showed that spinosin significantly and dose-dependently augmented pentobarbital (45 mg/kg, i.p.)-induced sleep, reflected by increased sleep time and reduced sleep latency assessed with the loss-of-righting reflex, and these effects were potentiated by the 5-hydroxytryptamine (serotonin) precursor 5-hydroxytryptophan (5-HTP, 2.5 mg/kg,i.p.). With a subhypnotic dose of pentobarbital (28 mg/kg, i.p.), spinosin significantly increased the rate of sleep onset and exhibited a synergistic effect with 5-HTP (2.5 mg/kg, i.p.). Pretreatment with p-chlorophenylalanine (PCPA, 300 mg/kg, s.c.), an inhibitor of tryptophan hydroxylase, significantly decreased pentobarbital-induced sleep time, and spinosin significantly reversed this effect. The dopamine precursor L-3-(3, 4-dihydroxyphenylalanine (L-DOPA) reduced pentobarbital-induced sleep, an effect not significantly affected by spinosin. These results suggest that spinosin potentiated pentobarbital-induced sleep via a serotonergic mechanism.     

加锡果宁的中枢抑制作用

加锡果宁(Ed)在1/20～1/8 LD_(50)剂量下对小鼠可明显缩短巴比妥或安定的翻正反射消失潜伏期和延长睡眠时间,增强乙醚的麻醉作用,减少自发活动。对某些镇痛药也有增强作用,使家兔脑电呈高幅慢波。延长大鼠总睡眠和慢波睡眠时间,与ip 30mg/kg戊巴比妥钠的作用强度相似,但Ed抑制异相睡眠时间比戊巴妥钠更强。     

Boosting effect of morphine on alcohol drinking is suppressed not only by naloxone but also by the cannabinoid CB1 receptor antagonist,SR 141716

The present study investigated the effect of the cannabinoid CB(1) receptor antagonist, SR 141716 (N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-3-pyrazole-carboxamide), on the ability of low and high doses of morphine to, respectively, augment and suppress voluntary alcohol intake in selectively bred Sardinian alcohol-preferring rats. Acute administration of a low dose of morphine (1 mg/kg, s.c.) produced a specific and marked increase in alcohol intake, which correlated with an increase in blood alcohol levels and was prevented by either SR 141716 (0.3 mg/kg, i.p.) or naloxone (0.1 mg/kg, i.p.). A higher dose (10 mg/kg, s.c.) of morphine reduced both alcohol and food intakes and produced sedation and hypomotility. The suppressant effect of morphine on alcohol intake was blocked by naloxone (0.1 mg/kg, i.p.) but not by SR 141716 (0.3 mg/kg, i.p.). These results are in agreement with those showing the ability of SR 141716 to antagonize the appetitive and positive reinforcing properties of morphine and add further support to the hypothesis of the existence of a functional link between the action of opioids and of cannabinoids.     

Behavioural effects in rats of morphine and amphetamine and of a combination of the two drugs

Summary Small single doses of morphine (1 mg/kg s.c.) and of amphetamine (1 mg/kg s. c.) induce excitation in rats. Locomotion and rearing are selectively stimulated by amphetamine, and grooming by morphine. Higher doses of morphine (5 mg/kg s. c.) cause sedation or catalepsy (20 mg/kg s. c.) but no stereotypies are seen as after amphetamine (10 mg/kg s. c.). Repeated doses of morphine induce stereotyped behaviour, which is inhibited by nalorphine. An antagonism between morphine and amphetamine is demonstrated but the anti-amphetamine effect of morphine is different from that of the neuroleptic drugs. Catecholamines in the basal ganglia may play a role in these behavioural effects of morphine.     

A TRH analog (DN-1417): effects on local cerebral glucose utilization in conscious and pentobarbitalized rats determined by the autoradiographic 2-deoxy-[14C]glucose method

Effects of a TRH (thyrotropin-releasing hormone) analog, DN-1417 (gamma-butyrolactone-gamma-carbonyl-L-histidyl-L-prolinamide citrate), with regard to the rate of local cerebral glucose utilization (LCGU) were assessed using the autoradiographic 2-deoxy-D-[14C]glucose method to clarify the possible sites of action in conscious and pentobarbitalized rats. DN-1417 (0.5-5 mg/kg, i.v.) significantly shortened the pentobarbital-induced sleeping time in a dose dependent manner, and this effect of DN-1417 was reduced by intracerebroventricular (i.c.v.) pretreatment with atropine methylbromide (20 micrograms). DN-1417 (5 mg/kg, i.v.) by itself slightly increased the LCGU in the thalamus dorsomedial nucleus and mammillary body and significantly increased it in the septal nucleus. Pentobarbital (30 mg/kg, i.v.) alone produced a marked and diffuse reduction in LCGU throughout the brain at a rate of about 46% of the control. DN-1417 (5 mg/kg, i.v.) markedly reversed the reduction of LCGU induced by pentobarbital. The antagonistic effect of DN-1417 in LCGU was about twice as potent as that of TRH. Locally, significant reversal effects by DN-1417 were observed in the hypothalamus, septal nucleus, hippocampus, mammillary body, thalamus dorsomedial nucleus, caudate-putamen, nucleus accumbens, pontine gray matter and so on. These actions of DN-1417 were almost completely abolished in all areas except for the visual cortex under the condition of pretreatment with atropine methylbromide (20 micrograms, i.c.v.). On the other hand, pimozide (1 mg/kg, i.p.) augmented the actions of DN-1417. Thus, DN-1417 seems to act on the level of consciousness via a reticulo-thalamo-cortical system, and reverses the LCGU reduction induced by pentobarbital via a cholinergic mechanism. The hypothalamus appears to be a crucial site in mediation of the antagonistic action of DN-1417 on pentobarbital.     

An analysis of naltrexone and naloxone's possible agonistic actions in the dog

Naltrexone (0.01-2.0 mg/kg, i.v.) produced dose-dependent EEG slowing in the conscious dog as did morphine (0.5-8 mg/kg, i.v.) and fentanyl (5-20 micrograms/kg, i.v.). However, the dose-response curve for naltrexone was not parallel to the morphine or fentanyl dose-response curves. Morphine and fentanyl but not naltrexone also produced dose-dependent miosis and increased the skin twitch reflex latency. When administered into the fourth cerebral ventricle naltrexone (60 micrograms), morphine (80 micrograms) and ethylketazocine (30 micrograms) produced EEG slowing. Again, naltrexone did not alter the skin twitch latency whereas morphine lengthened it and ethylketazocine reduced it. The pharmacological profiles obtained from different routes of administration indicate that naltrexone is clearly different from morphine, fentanyl and ethylketazocine. However, naltrexone may act as a partial agonist in the production of EEG slowing at a previously unidentified opioid receptor.     

Role of 5-hydroxytryptamine in morphine-, pethidine-, and methadone-induced hypothermia in rats at low ambient and room temperature.

1 The effect of morphine (10 or 20 mg/kg s.c.), pethidine (25 or 50 mg/kg s.c.) or methadone (4 or 8 mg/kg s.c.) on the body temperature of nontreated and p-chlorophenylalanine-pretreated rats was studied at room (21+/-0.2 degrees C) or low ambient (12+/-0.2 degrees C) temperature. 2 Neither pethidine nor smaller doses of morphine and methadone altered the mean rectal temperature of rats kept at room temperature but larger doses of morphine and methadone produced significant hypothermia. 3 All narcotic analgesics at doses used in the present investigation produced significant hypothermia in rats maintained in a low ambient temperature. The hypothermia was prevented by naloxone (1 mg/kg s.c.). 4 The administration of p-chlorophenylalanine (PCPA, 320 mg/kg i.p.) 48 h before the narcotic injection prevented the fall in body temperature both at room and low ambient temperature. 5 The administration of narcotic analgesics at doses, which when administered by themselves did not alter the body temperature of rats, produced significant hyperthermia in rats pretreated with PCPA. 6 When rats pretreated with PCPA were given 5-hydroxytryptophan (75 mg/kg s.c.) 30 min before narcotic administration, the usual response to narcotics was restored. 7 It appears that pethidine and methadone as well as morphine have both hyperthermic and hypothermic actions in rats and that 5-hydroxytryptamine may be involved in the narcotic-induced hypothermia not only at room temperature but also at low ambient temperature.     

Hypothalamo-pituitary-adrenocortical (HPA) function in the morphine dependent rat (author's transl)]

Morphine dependence was induced by ten daily administrations of morphine with gradually increasing dosage (40--160 mg/kg/day s.c.) to male Sprague-Dawley rats, the dosage being divided in 2/day for the first 8 days and 4/day for the last 2 days. Diurnal variation in body weight in morphine dependent rats was the same as in naive rats. Although body temperature in the naive rats showed a diurnal variation with the highest at 3:00 and the lowest at 15:00, in the morphine dependent rats there was no distinct variation. Plasma corticosterone level (PC) in naive rats showed diurnal variation with the peak at 21:00 and the trough at 9:00. PC in morphine dependent rats showed the same diurnal variation as did the naive rats, while such disappeared following pentobarbital anesthesia (80 mg/kg i.p. for 45 min) and PC was low all during the day. The PC increase following formalin administration to morphine dependent rats was higher than in naive rats. 0.1 mg/kg s.c. of dexamethasone completely inhibited PC increase after formalin in naive rats, but the dexamethasone inhibition in morphine dependent rats was not complete even with a larger dose, i.e. 10 mg/kg s.c. Diurnal variations and other differences were not detected in the adrenal response to ACTH (in vivo, in vitro) between naive and morphine dpendent rats. These results suggest that HPA function takes part in the development of morphine dependence.     

Effect of selective monoamine oxidase inhibitors on the morphine-induced hypothermia in restrained rats

Morphine (30 mg/kg i.p.) produced a hypothermic effect in restrained rats which was antagonized by naloxone pretreatment (10 mg/kg s.c.). This hypothermia was inhibited by deprenyl pretreatment (5 mg/kg i.p.) and by beta-phenylethylamine treatment (25 mg/kg i.p.). However, the effect of morphine was partially potentiated when a higher dose of deprenyl (10 mg/kg i.p.) was administered. Pretreatment with clorgyline (1 mg/kg i.p.) potentiated the morphine-induced hypothermia. In contrast, the effect of morphine was antagonized when a higher dose of clorgyline was used (5 mg/kg i.p.). Based on these results, a possible role of brain serotonin and dopamine in the thermoregulatory effects of morphine is proposed in this paper.     

Effect of endosulfan pretreatment on organ weights and on pentobarbital hypnosis in rats

The effects of ebdosulfan on the weights of the liver, adrenal and ovary, on pentobarbital blood and brain levels and on sleeping time (ST) have been investigated in female rats after daily oral doses of 0, 1.0, 2.5 and 5.0 mg/kg for a period of 7 or 15 days. No significant change in body weight was observed. With higher doses (2.5–5.0 mg/kg) the liver weight was significantly increased, but ovary and adrenal weights did not increase. Endosulfan treatment shortened sleeping time, while induction time was significantly increased. The concentration of pentobarbital in the blood and brain of rats after 30 min and upon awakening indicated that there was a significant decrease at 30 min. No change at awakening was observed in endosulfan-treated rats as compared to controls. It is suggested that endosulfan may shorten the duration of pentobarbital-induced sleep, perhaps by induction of hepatic microsomal enzyme activity.     

Effect of morphine on the accumulation of DOPA after decarboxylase inhibition in the rat.

Acute systemic administration of morphine (10 mg/kg s.c.) to rats increased in vivo tyrosine hydroxylation in the striatum measured as the accumulation of DOPA after decarboxylase inhibition. DOPA accumulation reached a maximum 30-60 min after morphine. The morphine antagonist naloxone (1, 10 or 100 mg/kg s.c.) did not significantly after DOPA accumulation. However, naloxone completely antagonized the effect of morphine. The DA agonist apomorphine decreased and the DA antagonist haloperidol increased DOPA accumulation. The effect of apomorphine (0.05 mg/kg) was counteracted by morphine. Naloxone did not significantly change the accumulation of DOPA after apomorphine or after haloperidol. In rats treated with gamma-butyrolactone (GBL) or with reserpine DOPA accumulation was not altered by treatment with morphine or naloxone. However, the inhibiting effect of apomorphine (0.5 mg/kg) on the accumulation of DOPA in rats treated with reserpine was weakly counteracted by morphine (0.5 mg/kg) on the accumulation of DOPA in rats treated with reserpine was weakly counteracted by morphine (10 mg/kg s.c.). Since the effects of morphine on the apomorphine-induced inhibition of DOPA accumulation were antagonized by naloxone, we suggest that the effects on striatal DOPA accumulation produced by morphine were mediated via opioid receptors and not directly via DA receptors.     

Antagonism of gut,but not central effects of morphine with quaternary narcotic antagonists

Naltrexone methylbromide and naloxone methylbromide, quaternary derivatives of naltrexone and naloxone respectively, are assumed to act peripherally. Both compounds reversed the intestinal stimulating effect of morphine in the dog. Naltrexone methylbromide 5 mg/kg s.c. blocked morphine-induced intestinal spike potentials for 50 min while intravenous doses caused antagonism for only 25 min. The antagonism by the s.c. route approximated that produced by naltrexone 0.2 mg/kg s.c. In morphine-dependent dogs, naltrexone methylbromide did not appear to antagonize morphine centrally in doses ranging from 0.25 to 50 mg/kg s.c. since it did not induce behavioral signs of narcotic withdrawal. Similarly, i.v. naloxone methylbromide was also able to reverse morphine-induced intestinal spike potential in dogs but the protection lasted only 25 min. In rats, naltrexone methylbromide 10 and 30 mg/kg i.p. neither reversed morphine block of PGF_2α-induced diarrhea nor antinociception. This suggests a lack of CNS narcotic antagonism in both tests. In mice, naltrexone methylbromide, 60–720 mg/kg orally and 3–140 mg/kg i.p. failed to block morphine inhibition of prostaglandin F_2α-induced diarrhea. Paradoxically, in this species, 30 mg/kg s.c. of naltrexone methylbromide appeared to cross the blood-brain barrier since this dose reversed morphine-induced antinociception. In conclusion, naltrexone methylbromide effectively antagonizes the acute gut stimulating effect, but not the chronic behavioral effect of morphine administration in dogs. Based upon the antinociception test, naltrexone methylbromide does not cross the blood-brain barrier in rats but may in mice. Morphine inhibits prostaglandin F_2α-induced diarrhea by a central mechanism in rodents.     

Enhancement of pharmacologic responses of pentobarbital by dopram

The effect of Dopram (doxapram hydrochloride, A. H. Robins Co.) on the pharmacologic responses to pentobarbital was evaluated. In naive and pentobarbital-tolerant mice, Dopram was shown to enhance significantly sodium pentobarbital-induced narcosis in a dose-related manner. The effect of the duration of action of Dopram on pentobarbital narcosis also was assessed. It was observed that Dopram (40 mg/kg, i.p.) significantly increased pentobarbital-induced narcosis even when administered 2 hr prior to challenge with sodium pentobarbital (60 mg/kg, i.p.) A significantly increased hypothermic response to sodium pentobarbital was seen in Dopram-treated animals. The half-life of pentobarbital in brain and serum was shown to be increased significantly in animals receiving Dopram, 40 mg/kg, i.p. The waking brain and serum pentobarbital concentrations were not significantly different in either group. These studies show that Dopram potentiates pentobarbital's effects. Further study is necessary to determine the sites of operation and mechanism of this potentiation.     

Cross-tolerance between morphine- and bombesin-induced inhibition of intestinal transit in rats

Intracerebroventricular (i.c.v.) injection of either morphine or bombesin to rats inhibits intestinal transit of an intraduodenally administered radiochromium marker. In this work, we show that tolerance develops to this effect of bombesin after i.c.v. infusion of the peptide (0.5 micrograms/h for 4 days via an s.c. implanted Alzet 2001 osmotic minipump). Tolerance also develops to the inhibition of intestinal transit associated with i.c.v. morphine after s.c. injections of morphine. Bombesin-induced delay of transit is not attenuated by naltrexone (10 mg/kg, s.c.), a standard narcotic antagonist. Nevertheless, two-way cross-tolerance develops between bombesin and morphine in this system. This is a surprising result since both bombesin and morphine are believed to act on different receptors and cause opposite effects on intestinal motility in rats.     

Protection by opioids against gastric lesions caused by necrotizing agents

The synthetic opioid met-enkephalin analog [D-Ala2, MePhe4, Met(0)5ol] enkephalin (DAMME) and the opiate morphine injected intraperitoneally to rats at doses of 0.5-2 and 5-20 mg/kg, respectively, showed a protective effect on gastric damage induced by oral administration of necrotizing agents (0.6 N HCl or 0.2 N NaOH solutions, 1 ml/rat). The protection was prevented by naltrexone (10 mg/kg s.c.), an opioid antagonist with long-lasting activity. Histological sections of mucosal samples from animals pretreated with morphine (10 mg/kg i.p.) and DAMME (1 mg/kg i.p.) showed less alteration of the columnar epithelium, with a normal glandular structure, than untreated rats. A mediation of prostaglandins is suggested, since indomethacin (10 mg/kg s.c.) significantly reduced the protective effects of opioids.     

Sedation produced by prostaglandins is not a nonspecific fatty acid effect

The fatty acid specifity of the depressant actions associated with prostaglandin (PG) administration was studied in mice. Administration of PG-E₂ (0.4 and 1.0 mg/kg) or PG-D₂ (0.4 and 4 mg/kg) significantly potentiated pentobarbital sleeping time. Arachidonic acid (3.3 mg/kg) administration also significantly potentiated pentobarbital sleeping time. Pretreatment with indomethacin (3 mg/kg) or ibuprofen (10 mg/kg) inhibited the potentiation of pentobarbital sleeping time produced by arachidonic acid. A nonspecific fatty acid (11,14,17-eicosatrienoic acid), which cannot be incorporated into the PG synthetic scheme, did not potentiate pentobarbital sleeping time. These results imply that the depressant activity associated with PG administration is a specific PG-induced action rather than a general effect of long-chain unsaturated fatty acids.