Possible mediation of catecholaminergic pathways in the antinociceptive effect of an extract of Cannabis sativa L.

An extract of cannabis (5 and 15 mg/kg expressed as delta 9-THC) orally administered to rats caused an elevation of the nociceptive threshold (tail-flick latency and vocalization tests). Naloxone and naltrexone (blockers of mu-type opiate receptors) as well as MR 1452 (blocker of kappa opiate receptors) did not prevent the antinociceptive effect of cannabis when used at the dose of 2 mg/kg SC; only a high dose (10 mg/kg SC) of these narcotic antagonists partially blocked cannabis antinociception. ICI 154, 129, an antagonist of delta-type opiate receptors, failed to prevent the cannabis-induced rise in nociceptive threshold when used at a dose of 2 mg/kg SC but produced a significant effect at 10 mg/kg SC. While the role of opiate receptors does not seem fundamental to cannabis antinociception, the clear-cut effectiveness shown by 6-hydroxydopamine (a neurotoxin which causes a degeneration of catecholamine-containing terminals) in reducing cannabis antinociception is indicative of a participation of catecholamines in the phenomenon.

Hypothermia elicited by some prodynorphin-derived peptides: opioid and non-opioid actions.

Prodynorphin-derived peptides were tested for their effects on body temperature after intracerebroventricular administration to unrestrained male rats. Dynorphin A (Dyn A) (5 and 10 nmol) and Dynorphin A-(1-32) (Dyn A-(1-32) (2.5 and 5 nmol) lowered body temperature with a maximum approximately 30 min after administration. Dyn B (up to 50 nmol) did not induce hypothermia. Lower doses of all peptides did not alter body temperature. The hypothermic effect was significantly, but not completely prevented by MR1452 (30 nmol), a preferential antagonist of the kappa receptor, administered intracerebroventricularly. Naloxone, a mu receptor antagonist, naltrexone, its long acting analog up to doses of 100 nmol, as well as MR1453, the (+)-enantiomer of kappa antagonist MR1452 with no opioid binding properties, did not prevent the hypothermic effect. Moreover, episodic barrel rolling and bizarre postures elicited by Dyn A and Dyn A-(1-32) were reduced in rats pretreated i.c.v. with MR1452 (30 nmol), but not with naloxone (up to 100 nmol). Interestingly, des-Tyr-Dynorphin A (Dyn A-(2-17)), a fragment with virtually no opioid binding potential, was 4 times less potent that Dyn A in inducing hypothermia. These findings are consistent with the hypothesis that prodynorphin-derived peptides effects are not exclusively opioids in nature.

Possible involvement of dynorphinergic system in nociceptive transmission at spinal level.

The opioid peptide dynorphin1-32 (DYN1-32, 25 nmol) intrathecally administered causes, in the rat, an elevation of nociceptive threshold of longer duration than that of DYN A, as ascertained by vocalization test. Comparative findings obtained with tail flick test allow to differentiate antinociception from motor dysfunction. The breakdown of DYN A at spinal level is very rapid. The electrical stimulation of the tail associated to a restraint condition of the rat produces a significant increase of immunoreactive DYN in cervical, thoracic and lumbar segments of spinal cord, therefore indicating a correlative, if not causal, relationship between the spinal dynorphinergic system and aversive stimuli.

Regional distribution of immunoreactive dynorphin A in the human gastrointestinal tract.

Immunoreactive dynorphin A (ir-Dyn A) was detected throughout the human gastrointestinal tract by a validated radioimmunoassay. Moreover, the stability of 125I-Dyn A during extraction procedures was confirmed by high performance liquid chromatography. Levels of ir-Dyn A were higher in the stomach and in the small bowel. In tissue samples separated into the main layers composing the gut wall (muscularis externa, submucosa and mucosa) ir-Dyn A was uniformly distributed. An exception was the colon, where concentrations were higher in the muscular portion. Gel permeation chromatography on samples of mucosa and muscularis externa extracts of ileum and gastric fundus, showed immunoreactive material eluting in several forms of apparently higher molecular weight than Dyn A, while only a minor peak was found to coelute with authentic Dyn A.

Gi proteins and calcium in dynorphin-induced hypothermia and behaviour.

The intracerebroventricular (i.c.v.) administration of pertussis toxin (0.5 microgram) to rats significantly reduced the hypothermic and behavioural effects (episodic bizarre postures characterized by limb rigidity and followed by barrel rolling) induced by i.c.v. dynorphin A (10 micrograms). These central effects of dynorphin A thus appear to be initiated at a receptor site that interacts with G proteins substrates sensitive to pertussis toxin. Dynorphin A-induced hypothermia was also significantly reduced by i.c.v. pretreatment with the Ca2+ antagonist, verapamil (10 micrograms), although verapamil per se did not modify the behavioural effects elicited by the peptide.

Antinociceptive activity of salmon calcitonin injected intrathecally in the rat.

Salmon calcitonin injected intrathecally in unanesthetized rats produced long-lasting, dose-dependent elevations of nociceptive threshold as measured in the hot plate test. This antinociceptive action was nonopiate in nature as it was uninfluenced by the narcotic antagonists naloxone and MR 1452; moreover, the peptide was still able to raise the nociceptive threshold in morphine-tolerant rats. It is suggested that the spinal cord may represent one of the sites of action for calcitonin-induced antinociception.

Evidence that the kappa agonist U50488H has non-opioid actions.

The antagonism of the antinociceptive effects of various kappa-opioid agonists has been studied in the mouse abdominal constriction test. Naloxone produced a much smaller degree of antagonism of U50488H than it did of two other kappa-agonists, U69593 and tifluadom. The kappa-selective antagonist, norbinaltorphimine, also failed to shift the dose-response curve to U50488H in this test, despite producing considerable antagonism of the U50488H effect in the rotarod test and of U69593 in both experimental situations. These results are suggestive of a non-opioid component to the action of U50488H in the abdominal constriction test. At high concentrations, U50488H, but not U69593, also showed non-opioid effects in reducing contractile activity in the field-stimulated isolated guinea-pig ileum, as demonstrated by the profile of antagonism seen with beta-chlornaltrexamine and naloxone. These results suggest that U69593, rather than U50488H, may be the kappa-agonist of choice to use, particularly in in-vivo experiments.

Nonsteroidal anti-inflammatory agents. Part 17: Stereomeric o-, m-tolyl- and anisyl-biphenylyl-hydroxypropionic acids.

As a part of wider research project on chiral anti-inflammatory arylacanoic acids, the 3-(o- and m-)-(methyl and methoxy)-phenyl-2-biphenylyl-3-hydroxypropionic acids 3a-d were synthesized and resolved in their optically active erythro and threo stereomers, which were submitted to the carrageenan induced rat paw edema test. With respect to the p-isomers, only the threo p-methoxy substitution enhances the anti-inflammatory activity. Some conclusions on structure-activity relationship are discussed.

Nonsteroidal antiinflammatory agents. Part 16: Stereomeric 3-aryl-biphenylyl-hydroxy-propionic acids.

As part of a wider research project on structure-activity relationships of chiral arylalkanoic acids, stereomeric aryl- biphenylyl-hydroxypropionic acids 3a-d have been prepared and their antiinflammatory activity evaluated. Diastereomeric racemic erythro- and threo-acids have been synthesized by reaction of alpha-lithiated biphenylyl-acetic acid salts with the appropriate aldehyde. They were separated, and after attribution of their relative configuration by 1H-NMR analysis, resolved. The antiinflammatory activities of the enantiomeric potassium salts were determined by the carrageenan test.

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.

Nonsteroidal antiinflammatory agents. XVIII - Stereomeric optically active halogenophenyl-biphenylyl-hydroxypropionic acids.

The optically active stereomers of some 3-(fluoro-, chloro-, bromophenyl)-2-biphenylyl-3-hydroxypropionic acids were prepared and tested for antiinflammatory activity. Surprisingly, the four bromo-isomers were the most active ones, particularly in the threo configuration.

Differential effects of selective brain lesions on hypothalamic and pituitary ir-dynorphin.

Selective radiofrequency and neurotoxic lesions of the serotonergic pathways caused in the rat a significant reduction of ir-dynorphin A and B in the hypothalamus but not at pituitary level. These data confirm that dynorphin-related peptides are regulated independently in these areas.