E. Cavicchini

Distinguishable effects of intrathecal dynorphins, somatostatin, neurotensin and s-calcitonin on nociception and motor function in the rat

&NA; We determined the effects on nociceptive threshold and motor function of dynorphin‐gene products, dynorphin A‐(1–32) (DYN A‐(1–32), DYN A‐(1–8), DYN B and DYN B‐29 and the non‐opioid peptides somatostatin, neurotensin and salmon calcitonin (s‐CT) after intrathecal administration in the rat. DYN A‐(1–32) (25 nmol) produced maximal elevation of tail‐flick latency accompanied by severe hind limb paralysis and tail flaccidity lasting 6 h and still present at 24 h in several animals. Antinociception evaluated by the vocalization test wore off within 2 h. A lower dose of the peptide (6.25 nmol) did not alter the tail‐flick reflex and motor function but significantly elevated the vocalization threshold. The other dynorphins showed weaker, short‐lasting activity on the nociceptive threshold, the order of potency being as follows: DYN B‐29 > DYN B > DYN A‐(1–8). On the other hand, at the high doses DYN B (100 nmol) and DYN B‐29 (50 and 100 nmol) caused moderately severe hind limb paralysis whereas DYN A‐(1–8) did not cause any motor impairment up to the dose of 100 nmol. MR 1452, a relatively preferential antagonist of the &kgr; opioid receptor, prevented both the antinociceptive and motor effects of dynorphins. Intrathecal somatostatin (25 nmol) had a profile of activity superimposable on that of DYN A‐(1–32): long‐lasting (up to 24 h) elevation of tail‐flick latency with hind limb paralysis and a shorter (4 h) elevation of the vocalization threshold. MR 1452 did not modify these effects. Intrathecal neurotensin (25 nmol) and s‐CT (0.5 nmol) did not alter tail‐flick latency or vocalization threshold. However, adopting the hot plate as the analgesimetric test, both peptides elevated the time of hind paw licking, taken as an index of nociception. No signs of motor dysfunction were observed at the doses employed.

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.

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.

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.

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.

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.

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 Δ9-THC) orally administered to rats caused an elevation of the nociceptive threshold (tail-flick latency and vocalization tests). Naloxone and naltrexone (blockers of μ-type opiate receptors) as well as MR 1452 (blocker of κ 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 δ-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.

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.

Bivalent opioid peptides synthesized from μ selective monomers display preferential selectivity for δ receptors

Abstract A series of dimeric opioid peptides derived from μ selective compounds was synthesized to investigate whether μ and δ receptors coexist as distinct recognition sites on the same receptor complex. Some compounds were several times more potent than the corresponding monomers in the MVD (mouse vas deferens) smooth muscle preparation, which is rich in δ receptors, but yet retaining substantial activity in the GPI (guinea pig ileum). It is suggested that δ receptors might differ from μ receptors in that they possess an additional accessory recognition site, to which could bind a particular amino acid residue present in the second halves of these bivalent ligands. This residue could play the role of “address” at δ opioid receptors.

Effect of calcitonin-related peptides on nociception and thermoregulation of the rat

3. Motility of the ureter: Sequential scintigraphic studies of urinary transport in healthy volunteers after intravenous application of metamizol, pitofenon or placebo, respectively, showed a statistically significant decrease of urinary transport against gravitation after mstamizol, and in a lesser degree after pitofenon. After upright positioning, the urinary outflow towards the bladder was faster after metamizol compared with the reference substances. Contractility of gallbladder: -In sequential scintigraphic studies of the gallbladder a significant diminution of the ceruletid-provoced contraction of the gallbladder after metamizol was demonstrated compared with placebo, consequently followed by a lowering of bile outflow from the gallbladder. Conclusion: Nuclear medical investigations clearly demonstrate the diminution of the tonus of smooth muscle of ureter and gallbladder, and substantiate by this way the spasmolytic effect of the drug.