Prostaglandins in the brain of rats given, acutely, and chronically, a hyperthermic dose of met-enkephalin.

An enhanced prostaglandinlike activity is shown in homogenates of brain from rats treated intracerebroventricularly with 100 microgram of metenkephalin. The increase is significantly reduced by naloxone pretreatment. A relationship is proposed between generation of prostaglandins in the brain following met-enkephalin administration and hyperthermic effect of the opiatelike factor in the rat. Normalization of prostaglandinlike activity following chronic administration of met-enkephalin in the rat may also account for the development of tolerance to its thermic effect.

Investigations on behavioral effects of an extract of Cannabis sativa L. in the rat.

The behavioral responses of the rat to an extract of Cannabis sativa were examined after IP injection of 5, 15 and 30 mg/kg (expressed as delta 9 tetrahydrocannabinol). The lowest dose of the extract induced stereotyped behavior (rhythmic head movements, intermittent gnawing and sniffing) together with hypersensitivity to stimuli and hyperthermia. The administration of higher doses of the extract resulted, initially, in similar behavioral effects but of greater intensity, followed by a cataleptic state alternating with atonic muscular prostration; rectal temperature was decreased. Pre-treatment with 6-hydoxydopamine (6-OHDA, which produces degeneration of catecholamine-containing nerve terminals)or pimozide (blocker of dopamine receptors) significantly reduced both stereotype and hyperreactivity. Thermic effects were also antagonized by 6-OHDA pre-treatment. Cannabis-induced catalepsy was enhanced by pimozide but reduced by atropine (3 mg/kg SC). These results support the hypothesis that catecholamines play an important role in the complex behavioral effects of cannabis.

Effects of Met-enkephalin on body temperature of normal and morphine-tolerant rats.

The endogenous opioid met-enkephalin intraventricularly adminstered to the rat at the dose of 100 microgram raised rectal temperature, whereas 400 microgram of the pentapeptide caused a diphasic effect, i.e., hypothermia followed by hyperthermia. Met-enkephalin was ineffective when administered i.p. The effects on temperature were substantially similar to those elicited, for both routes of administration, by morphine, which may either raise or lower rat temperature depending on the dose. More naloxone was required to antagonize thermic effects of met-enkephalin than morphine. Finally, there was a lack of effects on temperature for met-enkephalin centrally administered to morphine-tolerant animals, thus providing further evidence, in vivo, of cross tolerance between opiates and naturally occurring ligands of opiate receptors.

Evidence of an involvement of the opioid peptidergic system in the reaction to stressful conditions.

Rats exposed to combined cold and restraint exhibited reduced paw oedema following an injection of carrageenin. Under the same experimental conditions, the local inflammation became fully evident when animals were pretreated with naloxone, 5 mg/kg, s.c. The same dose of the narcotic antagonist also increased the intensity of gastric damage in restrained, cold-exposed rats. On the contrary, gastric ulcerations were practically inexistent in stressed rats treated with 10 mg/kg s.c. of morphine. It is suggested that the opioid peptidergic system is involved in the body's reactivity to stressful stimuli.

Effect of indomethacin on opioid-induced gastric protection in cold-restrained stress.

Morphine and the synthetic opioid met-enkephalin analog [D-Ala2, MePhe4, Met(0)5ol] enkephalin (FK 33-824) injected intraperitoneally to rats at doses of 5-20 and 0.5-2 mg/kg respectively showed a protective effect on gastric lesion induced by cold-restraint stress. This protective effect was abolished by pretreatment with indomethacin. This suggests a role for prostaglandins in the protection, induced by opioids of the gastric mucosa against the development of stress-induced ulcers.

Synthesis of carboxyalkylthio-triazoles and bicyclic derivatives with antiinflammatory and analgesic activity.

3-Carboxyalkylthio derivatives of 5-alkoxyphenyl-1,2,4-triazole were prepared, performing some substitutions both on carboxyalkyl chain, by lengthening it or introducing substituents with increasing molecular weight in alpha- at the carboxy group, and on N-4 atom in the triazole ring, by introducing an amino or methyl group, so that to vary steric conformation along with the lipophilicity of molecules. The corresponding bicyclic thiazolo-triazolone and triazolo-thiazinone derivatives, which represent the rigid models of carboxymethylthio- and carboxyethylthio- open structures, were also obtained. All the compounds show "in vivo" antiinflammatory activity, while only carboxyalkylthio derivatives of 4-amino- and 4-methyltriazole display an appreciable analgesic one. From the relief of some data on substituent present in the synthesized compounds, a structure-activity relationship is also suggested.

Correlations between histamine and opioid peptides on the modulation of inflammatory processes in rats exposed to stress.

The role of mast cell histamine in body reactivity of rats under experimental stressful conditions was studied. Animals submitted to chronic anaphylactoid reactions (by injecting compound 48/80 at the dose of 1 mg/kg, i.p., twice daily, for five days), when exposed to cold-restraint stress, exhibited a fully evident inflammatory response in the carrageenin-oedema test, whereas saline-treated rats, under the same experimental conditions, showed reduced paw oedema. Interestingly, a single injection of compound 48/80 increased the pituitary content of Beta-endorphin(ir), but chronic administration failed to produce this effect suggesting that some adaptation of the organism to repeated anaphylactoid reactions may occur. These results support the hypothesis of correlations between pituitary Beta-endorphin and mast cell histamine in the reactivity of the organism to stressful stimuli.

Peripheral and central opioid activity in the analgesic potency of morphine.

The role of neural histamine in morphine-analgesia and in morphine-induced potentiation of stress analgesia was studied. Pretreatment of rats with alpha-fluoromethylhistidine (alpha-FMH) (200 micrograms i.c.v./rat; daily for five days) increased the analgesic potency of morphine, centrally or peripherally injected, in the tail-flick assay. This increase was significantly blocked by i.c.v. or i.p. beta-funaltrexamine (beta-FNA) a mu selective irreversible opioid receptor antagonist, whereas i.c.v. injected naltrexone did not block the increased analgesic potency of the i.c.v. morphine. Rats subjected to cold-restrained stress (60 min at 4 degrees C) showed increased tail-flick latency, compared to the unstressed group. The analgesic potency of morphine was significantly greater in rats subjected to restraint with respect to unstressed rats. However, the inhibition of histamine biosynthesis by alpha-FMH significantly reduced cold-restraint analgesia in controls, and also inhibited the analgesic efficacy of the opiate. These results indicate that neural histamine may be responsible for pain response modifications observed in rats subjected to cold-restraint conditions, and of morphine-potentiation of stress analgesia. The data also suggest a close association between increased analgesic potency of morphine and inhibition of histaminergic effects, possibly implying a functional supersensitivity and an increase in opioid receptors.

Evidence of a key-role for histamine from mast cells in the analgesic effect of clomipramine in rats.

OBJECTIVE AND DESIGN: We investigated the role of neuronal and mast cell histamine in the analgesic effect of clomipramine. SUBJECTS: Male Sprague-Dawley rats (4-6 weeks old) were used (n = 228). TREATMENT: Clomipramine (10, 20 or 40 mg/kg i.p.) was injected in rats pretreated with [a] saline i.cv. or i.p., [b] alpha-fluoromethylhistidine (alpha-FMH, 200 microg i.cv.), [c] compound 48/80 (C48/80, 1 mg/kg i.p.). Other rats were pretreated with clomipramine, before C48/80. METHODS: Antinociceptive responses were determined before and 30, 60, 90, 120 min after drug injection by tail-flick (TFT) and hot-plate (HPT) tests. Results for each treatment group are given as mean %MPE +/- SEM (Student's t-test, ANOVA). RESULTS: Clomipramine produced no significant changes in TFT and HPT in saline- or alpha-FMH-pretreated rats. Following C48/80, clomipramine (10 and 20 mg/kg) produced a dose-related significant increase in latencies, between 30 and 120 min: 28.5 +/- 5.7 vs 8 +/- 1.6 (p < 0.05), 56 +/- 5 vs 9.2 +/- 1.9 (p < 0.01) in TFT; 31 +/- 4.3 vs 12 +/- 2.5 (p < 0.05), 46.2 +/- 6 vs 11.5 +/- 1.9 (p < 0.01) in HPT. Clomipramine (40 mg/kg, after C48/80) produced marked and persistent increase in latencies 83.2 +/- 4.2 vs 10.5 +/- 3 (p < 0.01) in TFT and 91.2 +/- 4.6 vs 10.5 +/- 3 (p < 0.01) in HPT, followed by symptoms of toxicity and death of some animals. In rats pretreated with clomipramine, C48/80 was unable to show antinociceptive effects on TFT and HPT. CONCLUSIONS: Results suggest that the antinociceptive effect of clomipramine may depend on mast cell histamine levels.

Modification of rat thermal responses to morphine by alpha-FMH suggests a role for neural histamine in morphine tolerance.

In rats, morphine may either raise or lower body temperature depending on the dose. A morphine dose of 50 mg/kg, i.p., consistently produced a nearly maximal hypothermic response in non tolerant rats, whereas this dosage induced an elevation of body temperature in tolerant rats. In rats pretreated with alpha-fluoromethylhistidine (alpha-FMH), an irreversible inhibitor of histidine decarboxylase which induces a reduction in brain histamine synthesis, this morphine dose of 50 mg/kg, i.p. produced an elevation of rectal temperature resembling that observed in morphine-tolerant rats. To confirm the suggestion that hyperthermic effects of the higher dose of morphine in morphine-tolerant rats or in alpha-FMH-pretreated rats could be related to a possible involvement of mediators of fever, e.g. prostaglandins, animals were pretreated with acetylsalicylic acid (aspirin, Bayer) 30 mg/kg, i.p., 60 min before morphine. Results showed that acetylsalicylic acid prevented the hyperthermic response of morphine, resulting in a fall in body temperature. Since morphine releases histamine and alpha-FMH inhibits histamine synthesis, our data demonstrating that an inhibitor of prostaglandin-synthetase showed efficacy only in animals responding with fever to the higher dose of the opiate, suggests a physiological antagonism between histamine and prostaglandins on mechanisms underlying hyper/hypothermic responses to morphine.

Evidence of correlations between mast-cell histamine and beta-endorphin (ir) from NIL-pituitary in the homeostasis.

This study was designed to characterize physiological events related to a single or repeated experimental anaphylactoid reactions (by Compound 48/80) in non-stressed or cold-restrained rats. Acute treatment with Compound 48/80 (1 mg/kg, i.p.) increases Beta-endorphin(ir) content in the neurointermediate lobe (NIL) of rat pituitary. Moreover, repeated treatment with Compound 48/80 showed tolerance effects. These animals, exposed to stressful conditions, exhibited a fully evident paw oedema following carrageenin oedema-test, whereas saline-pretreated rats, under the same experimental conditions, showed reduced local inflammation. Since Compound 48/80 produces characteristic, systemic, anaphylactoid reaction in the rat, with a very high degree of selectivity in its action, our results suggest that mast-cell histamine and Beta-endorphin from NIL pituitary are involved in the body's reactivity to stressful stimuli.

Histaminergic mechanisms in clonidine induced analgesia in rat tail-flick test.

The role of neural histamine in clonidine-analgesia and in clonidine-induced potentiation of stress analgesia was studied. Pretreatment of rats with alpha-fluoromethylhistidine (FMH) (200 ug icv/rat; daily for five days) increased the analgesic effect of the alpha 2-agonist clonidine on the spinal reflex of the tail-flick test. Rats subjected to cold-restraint stress (30 min at 4 degrees C) showed increased latency compared to the unstressed rats. The analgesic efficacy of clonidine was significantly greater in rats subjected to cold-restraint with respect to unstressed rats. However, the inhibition of histamine biosynthesis by FMH significantly reduced cold-restraint analgesia in saline-controls, and consistently increased the analgesic efficacy of the alpha 2-agonist, showing a maximum latency. Yohimbine exhibited high affinity as an antagonist for alpha 2-receptors, inducing hyperalgesic effects and antagonizing clonidine analgesia and clonidine-induced potentiation of cold stress analgesia. In FMH-pretreated rats, yohimbine failed to reverse clonidine analgesia and did not block the increased analgesic efficacy of clonidine in cold-restrained FMH-pretreated rats. Results of this study suggest that inhibition of histamine release through alpha 2-adrenoceptors on histaminergic axons may contribute to the analgesic efficacy of systemically injected clonidine, also confirming that neural histaminergic pathways are implicated in the mediation of pain response in particular conditions of stress.

Effects of morphine and met-enkephalin analogue on gastric lesions induced by indomethacin.

The effects of morphine HCl and a synthetic met-enkephalin analogue [D-Ala2,MePhe4,Met(O)5ol]enkephalin (FK 33-824) on gastric damage produced by the intraperitoneal administration of indomethacin (10 mg/kg i.p.) have been investigated. Rats intraperitoneally pretreated with morphine HCl (10 mg/kg i.p.) and FK 33-824 (1 mg/kg i.p.) showed a statistically significant reduction both of the number and intensity of lesions induced by indomethacin. This protection was reversed by naloxone HCl (2 mg/kg i.p.). The protective effect was not related to a reduction of gastric secretion since the antisecretory drug cimetidine (25 mg/kg i.p.) and methscopolamine bromide (10 mg/kg i.p.) did not significantly prevent mucosal damage under the same experimental conditions.

[Synthesis and pharmacological study of various 2-(alkylaminoalkyl)mercapto-5-aryl-1,3,4-oxadiazoles]. / Sintesi ed attività farmacologica di alcuni 2-(alchilamminoalchil)mercapto-5-aril-1,3,4-ossadiazoli.

Work was continued on the pharmacological study of the 1,3,4-oxadiazole nucleus using aroylhydrazines already used for the synthesis of anti-MAO compounds. S-alkylaminoalkyl derivatives of some 2-mercapto-5-aryl-1,3,4-oxadiazoles were prepared bearing in the 5-position a 3,4,5-trimethoxyphenyl, a 3,5-dimethoxy-4-ethoxyphenyl or a 3,4-dihydroxymethylenephenyl radical. When subjected to pharmacological investigation the compounds showed clear hypotensive activity partially antagonized by atropine and antispastic activity on smooth muscle.

[Research on monoamine oxidase inhibitors: synthesis of N-alkyl and N-aralkyl substituted ethylsyringoylhydrazides].

In continuation of previous work on compounds with anti-MAO activity, some alkyl and aralkyl-hydrazides of ethylsyringic acid (3,5-dimethoxy-4-ethoxybenzoic acid) were synthesized. Pharmacological examination showed that branching of the alkyl radical on the beta nitrogen to the carbonyl group increases anti-MAO activity which appears to be linked with the molecular dimensions of the alkyl group.

Prostaglandins in rat placenta following acute and chronic administration of morphine.

The objective of the present study was to obtain information on prostaglandin (PG) biosynthesis in placenta following narcotic administration. PG biosynthetic capacity was determined in whole rat placenta homogenates in the presence of Na arachidonate, by evaluating net production of PGs assayed against PGE1 on rat stomach strips. An enhanced prostaglandin-like activity is shown in homogenates of placenta from rats treated subcutaneously with 10 mg/kg of morphine. This increase was prevented by naloxone pre-treatment. Continual morphine administration during gestation, results in a normalization of placental biosynthetic capacity thus suggesting the development of a tolerance to the narcotic effect.