Cytokine-mediated inflammatory hyperalgesia limited by interleukin-13.

The effect of interleukin-13 (IL-13) on hyperalgesic responses to intraplantar (i.pl.) injection of carrageenin, E. coli endotoxin (LPS), bradykinin, tumour necrosis factor a (TNF-alpha), interleukin-1 beta (IL-1 beta), interleukin-8 (IL-8) and prostaglandin E(2) (PGE(2)) was investigated in a model of mechanical hyperalgesia in rats. Also, the cellular source of the IL-13 was investigated. IL-13, administered 30 min before the stimulus, inhibited responses to carrageenin, LPS, bradykinin, and TNF-alpha, but not responses to IL-1 beta, IL-8 and PGE2. IL-13, administered 2 hours before the injection of IL-1b, did not affect the response to IL-1b, whereas IL-13, administered 12 hours or 12 + 2 hours before the IL-1 beta, inhibited the hyperalgesia (- 35%, - 77%, respectively). In murine peritoneal macrophages, IL-13 administered 2 hours before stimulation with LPS, inhibited the production of IL-1 beta (- 67%) and PGE(2) (- 56%). IL-13 administered 12 hours before stimulation with LPS inhibited LPS-stimulated PGE(2) but not IL-1 beta. An anti-IL-13 serum potentiated responses to carrageenin, LPS, bradykinin and TNF-alpha (but not IL-1 beta and IL-8), as well as responses to bradykinin in rats depleted of mast cells with compound 40/80, but not in athymic rats. These data suggest that IL-13, released by lymphocytes, limits inflammatory hyperalgesia by the inhibition of the production TNF-alpha, IL-1 beta, IL-8 and PGs.

Chronic intrathecal cannulation enhances nociceptive responses in rats.

The influence of a chronically implanted spinal cannula on the nociceptive response induced by mechanical, chemical or thermal stimuli was evaluated. The hyperalgesia in response to mechanical stimulation induced by carrageenin or prostaglandin E2 (PGE2) was significantly increased in cannulated (Cn) rats, compared with naive (Nv) or sham-operated (Sh) rats. Only Cn animals presented an enhanced nociceptive response in the first phase of the formalin test when low doses were used (0.3 and 1%). The withdrawal latency to thermal stimulation of a paw inflamed by carrageenin was significantly reduced in Cn rats but not in Nv or Sh rats. In contrast to Nv and Sh rats, injection in Cn animals of a standard non-steroid anti-inflammatory drug, indomethacin, either intraperitoneally or into the spinal cord via an implanted cannula or by direct puncture of the intrathecal space significantly blocked the intensity of the hyperalgesia induced by PGE2. Cannulated animals treated with indomethacin also showed a significant inhibition of second phase formalin-induced paw flinches. Histopathological analysis of the spinal cord showed an increased frequency of mononuclear inflammatory cells in the Cn groups. Thus, the presence of a chronically implanted cannula seems to cause nociceptive spinal sensitization to mechanical, chemical and thermal stimulation, which can be blocked by indomethacin, thus suggesting that it may result from the spinal release of prostaglandins due to an ongoing mild inflammation.

Chronic intrathecal cannulation enhances nociceptive responses in rats

The influence of a chronically implanted spinal cannula on the nociceptive response induced by mechanical, chemical or thermal stimuli was evaluated. The hyperalgesia in response to mechanical stimulation induced by carrageenin or prostaglandin E2 (PGE2) was significantly increased in cannulated (Cn) rats, compared with naive (Nv) or sham-operated (Sh) rats. Only Cn animals presented an enhanced nociceptive response in the first phase of the formalin test when low doses were used (0.3 and 1 percent). The withdrawal latency to thermal stimulation of a paw inflamed by carrageenin was significantly reduced in Cn rats but not in Nv or Sh rats. In contrast to Nv and Sh rats, injection in Cn animals of a standard non-steroid anti-inflammatory drug, indomethacin, either intraperitoneally or into the spinal cord via an implanted cannula or by direct puncture of the intrathecal space significantly blocked the intensity of the hyperalgesia induced by PGE2. Cannulated animals treated with indomethacin also showed a significant inhibition of second phase formalin-induced paw flinches. Histopathological analysis of the spinal cord showed an increased frequency of mononuclear inflammatory cells in the Cn groups. Thus, the presence of a chronically implanted cannula seems to cause nociceptive spinal sensitization to mechanical, chemical and thermal stimulation, which can be blocked by indomethacin, thus suggesting that it may result from the spinal release of prostaglandins due to an ongoing mild inflammation

Bradykinin B1 and B2 receptors, tumour necrosis factor alpha and inflammatory hyperalgesia.

The effects of BK agonists and antagonists, and other hyperalgesic/antihyperalgesic drugs were measured (3 h after injection of hyperalgesic drugs) in a model of mechanical hyperalgesia (the end-point of which was indicated by a brief apnoea, the retraction of the head and forepaws, and muscular tremor). DALBK inhibited responses to carrageenin, bradykinin, DABK, and kallidin. Responses to kallidin and DABK were inhibited by indomethacin or atenolol and abolished by the combination of indomethacin + atenolol. DALBK or HOE 140, given 30 min before, but not 2 h after, carrageenin, BK, DABK and kallidin reduced hyperalgesic responses to these agents. A small dose of DABK+ a small dose of BK evoked a response similar to the response to a much larger dose of DABK or BK, given alone. Responses to BK were antagonized by HOE 140 whereas DALBK antagonized only responses to larger doses of BK. The combination of a small dose of DALBK with a small dose of HOE 140 abolished the response to BK. The hyperalgesic response to LPS (1 microg) was inhibited by DALBK or HOE 140 and abolished by DALBK + HOE 140. The hyperalgesic response to LPS (5 microg) was not antagonized by DALBK + HOE 140. These data suggest: (a) a predominant role for B2 receptors in mediating hyperalgesic responses to BK and to drugs that stimulate BK release, and (b) activation of the hyperalgesic cytokine cascade independently of both B1 and B2 receptors if the hyperalgesic stimulus is of sufficient magnitude.

Cytokine-mediated inflammatory hyperalgesia limited by interleukin-4.

1. The effect of IL-4 on responses to intraplantar (i.pl.) carrageenin, bradykinin, TNFalpha, IL-1beta, IL-8 and PGE2 was investigated in a model of mechanical hyperalgesia in rats. Also, the cellular source of the IL-4 was investigated. 2. IL-4, 30 min before the stimulus, inhibited responses to carrageenin, bradykinin, and TNFalpha, but not responses to IL-1beta, IL-8 and PGE2. 3. IL-4, 2 h before the injection of IL-1beta, did not affect the response to IL-1beta, whereas IL-4, 12 or 12+2 h before the IL-1beta, inhibited the hyperalgesia (-30%, -74%, respectively). 4. In murine peritoneal macrophages, murine IL-4 for 2 h before stimulation with LPS, inhibited (-40%) the production of IL-1beta but not PGE2. Murine IL-4 (for 16 h before stimulation with LPS) inhibited LPS-stimulated PGE2 but not IL-1beta. 5. Anti-murine IL-4 antibodies potentiated responses to carrageenin, bradykinin and TNFalpha, but not IL-1beta and IL-8, as well as responses to bradykinin in athymic rats but not in rats depleted of mast cells with compound 40/80. 6. These data suggest that IL-4 released by mast cells limits inflammatory hyperalgesia. During the early phase of the inflammatory response the mode of action of the IL-4 appears to be inhibition of the production TNFalpha, IL-1beta and IL-8. In the later phase of the response, in addition to inhibiting the production of pro-inflammatory cytokines, IL-4 also may inhibit the release of PGs.

Role of lipocortin-1 in the anti-hyperalgesic actions of dexamethasone.

1. The effect of dexamethasone, lipocorton-1(2-26) and an antiserum to lipocortin-1(2-26) (LCPS1) upon the hyperalgesic activities in rats of carrageenin, bradykinin, tumour necrosis factor alpha (TNF alpha), interleukin-1(2), interleukin-6 (IL-6), interleukin-8 (IL-8), prostaglandin E beta (PGE2) and dopamine were investigated in a model of mechanical hyperalgesia. 2. Hyperalgesic responses to intraplantar (i.pl.) injections of carrageenin (100 micrograms), bradykinin (500 ng), TNF alpha (2.5 pg), IL-1 beta (0.5 pg), and IL-6 (1.0 ng), but not responses to IL-8 (0.1 ng), PGE2 (100 ng) and dopamine (10 micrograms), were inhibited by pretreatment with dexamethasone (0.5 mg kg-1, subcutaneously, s.c., or 0.04-5.0 micrograms/paw). 3. Inhibition of hyperalgesic responses to injections (i.pl.) of bradykinin (500 ng) and IL-1 beta (0.5 pg) by dexamethasone (0.5 mg kg-1, s.c.) was reversed by LCPS1 (0.5 ml kg-1, injected s.c., 24 h and 1 h before hyperalgesic substances) and hyperalgesic responses to injections (i.pl.) of bradykinin (500 ng), TNF alpha (2.5 pg) and IL-1 beta (0.5 pg), but not responses to PGE2 (100 ng), were inhibited by pretreatment with lipocortin-1(2-26) (100 micrograms/paw). Also, lipocortin-1(2-26) (30 and 100 micrograms ml-1 and dexamethasone (10 micrograms ml-1) inhibited TNF alpha release by cells of the J774 (murine macrophage-like) cell-line stimulated with LPS (3 micrograms ml-1), and LCPS1 partially reversed the inhibition by dexamethasone. These data are consistent with an important role for endogenous lipocortin-1(2-26) in mediating the anti-hyperalgesic effect of dexamethasone, with inhibiton of TNF alpha production by lipocortin-1(2-26) contributing, in part, to this role. 4. Although arachidonic acid by itself was not hyperalgesic, the hyperalgesic response to IL-1 beta (0.25 pg, i.pl.) was potentiated by arachidonic acid (50 micrograms) and the potentiated response was inhibited by dexamethasone (50 micrograms, i.pl.) and lipocortin-1(2-26) (100 micrograms, i.pl.). Also, lipocortin-1(2-26) (30 and 100 micrograms ml-1) inhibited/abolished PGE2 release by J774 cells stimulated with LPS (3 micrograms ml-1). These data suggest that, in inflammatory hyperalgesia, inhibition of the induction of cyclo-oxygenase 2 (COX-2), rather than phospholipase A2, by dexamethasone and lipocortin-1(2-26) accounts for the anti-hyperalgesic effects of these agents. 5. The above data support the notion that induction of lipocortin by dexamethasone plays a major role in the inhibition by dexamethasone of inflammatory hyperalgesia evoked by carrageenin, bradykinin and the cytokines TNF alpha, IL-1 beta and IL-6, and provides additional evidence that the biological activity of lipocortin resides within the peptide lipocortin-1(2-26). Further, the data suggest that inhibition of lipocortin-1(2-26) of eicosanoid production by COX-2 also contributes to the anti-hyperalgesic effect of lipocortin-1.

Intrathecal administration of prostaglandin E2 causes sensitization of the primary afferent neuron via the spinal release of glutamate.

OBJECTIVE AND DESIGN: The present investigation was aimed at assessing the involvement of primary sensory neurons in the hyperalgesia induced by the intrathecal injection of PGE2, as well as whether the hyperalgesic effect was due to the spinal release of glutamate. MATERIAL: Male Wistar rats were used. METHODS: Hyperalgesia was measured using the rat paw pressure test. RESULTS: Intrathecal PGE2 (2.5-50 ng/rat) administration caused a dose-dependent hyperalgesia in both paws. Ipsilateral intraplantar injections of morphine (0.5-8 micrograms/paw) or SNAP (S-nitroso-N-acetyl-D,L-penicillamine, 50-200) micrograms/paw) dose-dependently antagonized spinally-induced PGE2 hyperalgesia (ANOVA, p < 0.001). Their antinociceptive effects were confirmed to be peripheral by abolition following pretreatment of the paws with L-NMMA (NG-monomethyl-L-arginine monoacetate), 50 micrograms/paw or with methylene blue (500 micrograms/paw). The spinally-induced PGE2 hyperalgesia was antagonized by intrathecal injections (9 micrograms) of AP5 (2-amino-5-phosphonopentanoate/2-amino-5) a selective NMDA receptor antagonist. CONCLUSIONS: Intrathecal administration of PGE2 seems to cause hyperalgesia by spinal sensitization of the primary afferent neuron through the release of glutamate.

Activation of the arginine-nitric oxide pathway in primary sensory neurons contributes to dipyrone-induced spinal and peripheral analgesia.

The objective of this study was to investigate the site of action of dipyrone in rat paw prostaglandin-induced hyperalgesia. The intracerebroventricular (i.c.v.) injection of dipyrone had no effect on the hyperalgesic response to prostaglandins. In contrast, intraplantar (i.pl.) and intrathecal (i.t.) injections produced dose-dependent analgesic effects. The analgesia observed following the intraperitoneal (i.p.), i.t., i.pl. or combined i.t. and i.pl. administration of dipyrone was abolished by pretreating the paws with L-NMMA (a nitric oxide synthase inhibitor) or methylene blue (MB, an inhibitor of soluble guanylate cyclase). These results support the suggestion that dipyrone-mediated antinociception results from a combined spinal and peripheral effect in the primary peripheral sensory neuron via stimulation of the arginine/cGMP pathway.

Cytokine-mediated inflammatory hyperalgesia limited by interleukin-10.

1. The effect of interleukin-10 (IL-10) upon the hyperalgesic activities in rats of bradykinin, tumor necrosis factor alpha (TNF alpha), interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6), interleukin-8 (IL-8), prostaglandin E2 (PGE2) and carrageenin were investigated in a model of mechanical hyperalgesia. 2. Hyperalgesic responses to bradykinin (1 micrograms) were inhibited in a dose-dependent manner by prior treatment with IL-10 (1-100 ng). 3. Hyperalgesic responses to TNF alpha (2.5 pg), IL-1 beta (0.5 pg) and IL-6 (1.0 ng) but not to IL-8 (0.1 ng) and PGE2 (50 ng and 100 ng) were inhibited by prior treatment with IL-10 (10 ng). 4. Hyperalgesic responses to carrageenin (100 micrograms) were inhibited by IL-10 (10 ng) when this cytokine was injected before but not after the carrageenin. 5. A monoclonal antibody to mouse IL-10 potentiated the hyperalgesic responses to carrageenin (10 micrograms) and TNF alpha (0.025 pg) but not that to IL-8 (0.01 ng). 6. In in vitro experiments in human peripheral blood mononuclear cells (MNCs), IL-10 (0.25-4.0 ng ml-1) inhibited in a dose-dependent manner PGE2 production by MNCs stimulated with IL-1 beta (1-64 ng ml-1) or endotoxin (lipopolysaccharide, LPS, 1 iu = 143 pg ml-1) but evoked only small increases in IL-1ra production. 7. These data suggest that IL-10 limits the inflammatory hyperalgesia evoked by carrageenin and bradykinin by two mechanisms: inhibition of cytokine production and inhibition of IL-1 beta evoked PGE2 production. Our data suggest that the latter effect is not mediated via IL-10 induced IL-Ira and may result from suppression by IL-10 of prostaglandin H synthase-2 (COX-2).

S14080, a peripheral analgesic acting by release of an endogenous circulating opioid-like substance.

1. The oral administration of a benzothiazolinone derivative (benzoyl-6 dihydro-2,3 benzothiazole), S14080, caused dose-dependent antinociception in the rat paw pressure test, which represents a model of mechanical hyperalgesia. S14080 had no significant effect on the inflammatory oedema induced by carrageenin or on the tail flick test, nor did it possess a notable antipyretic effect. 2. Post-treatment with S14080 dose-dependently antagonized the hyperalgesia induced by prostaglandin E2, bradykinin, dopamine and by the hyperalgesic cytokines reported to be released by carrageenin (tumour necrosis factor alpha, interleukin-1 and interleukin-8). 3. The blockade of prostaglandin E2-induced paw hyperalgesia by oral pretreatment of the rats with S14080 was abolished by prior intraplantar administration of either naloxone or NorBNI which are non-specific and specific kappa opioid antagonists, respectively. 4. Adrenalectomy abolished the oral antinociceptive effect of S14080. 5. Five consecutive daily injections of S14080 did not produce tolerance such as that seen with the central antinociceptive action of morphine. 6. As with peripherally acting opiates, the antinociceptive activity of S14080 was abolished by the intraplantar injection of agents which inhibit either arginine synthetase (NG-monomethyl-L-arginine) or the activation of guanylate cyclase (methylene blue). 7. We conclude that S14080 is a new type of peripheral antinociceptive which, in rats, acts mainly by releasing an endogenous, opioid-like substance from the adrenal glands.

Glutamate spinal retrograde sensitization of primary sensory neurons associated with nociception.

In the present investigation we have tested the hypothesis that spinal glutamate release by inflammatory stimuli causes hyperalgesia through sensitization of the primary sensory neurons associated with nociception. In these experiments, the rat paw hyperalgesia pressure test in which inflammatory hyperalgesia is blocked by the intraplantar administration of morphine (MPH) or SNAP, a NO donor was used. Glutamate and glutamatergic ionotropic agonists such as NMDA or AMPA injected intrathecally (i.t.) caused a dose-dependent hyperalgesia. Quisqualate or ACPD, both of which are glutamate metabotropic receptor agonists, had no hyperalgesic effect. The hyperalgesic response to glutamate and NMDA injected i.t. was antagonized by the intraplantar (i.pl.) injection of either MPH or SNAP. This observation indicates that the hyperalgesia induced by glutamate acting through an NMDA pre-synaptic receptor causes sensitization of the primary sensory neurons. Confirming that the analgesia by i.pl. injection of SNAP or MPH was due to an action in primary peripheral sensory neurons, it was shown that pretreatment of the paws with methylene blue (MB, an inhibitor of guanylate cyclase) or with MB and L-NMMA (an inhibitor of NO synthase) abolished their respective analgesic effect. AMPA i.t. induced hyperalgesia was not inhibited by either i.pl. administration of MPH or SNAP, indicating that its hyperalgesic capacity results from an action at a site other than the primary sensory neuron.(ABSTRACT TRUNCATED AT 250 WORDS)

Bradykinin initiates cytokine-mediated inflammatory hyperalgesia.

1. The hyperalgesic activities in rats of bradykinin, carrageenin and lipopolysaccharide (LPS) were investigated in a model of mechanical hyperalgesia. 2. Bradykinin and carrageenin evoked dose-dependent hyperalgesia with maximum responses of similar magnitude to responses to LPS (1 and 5 micrograms). 3. Hoe 140, an antagonist of BK2 receptors, inhibited in a dose-dependent manner hyperalgesic responses to bradykinin, carrageenin and LPS (1 microgram) but not responses to LPS (5 micrograms), prostaglandin E2, dopamine, tumour necrosis factor alpha (TNF alpha), IL-1, IL-6 and IL-8. 4. Responses to bradykinin and LPS (1 and 5 micrograms) were inhibited by the cyclo-oxygenase inhibitor, indomethacin and by the beta-adrenoceptor antagonist, atenolol. The effects of indomethacin and atenolol were additive: their combination abolished responses to bradykinin and LPS (1 microgram) and markedly attenuated the response to LPS (5 micrograms). 5. Antiserum neutralizing endogenous TNF alpha abolished the response to bradykinin whereas antisera neutralizing endogenous IL-1 beta, IL-6 and IL-8 each partially inhibited the response. The combination of antisera neutralizing endogenous IL-1 beta+IL-8 or IL-6+IL-8 abolished the response to bradykinin. 6. Antisera neutralizing endogenous TNF alpha, IL-1 beta, IL-6 and IL-8 each partially inhibited responses to LPS (1 and 5 micrograms). Increasing the dose of antiserum to TNF alpha or giving a combination of antisera to IL-1 beta+IL-8 or IL-6+IL-8 further inhibited responses to LPS (1 and 5 micrograms). 7. These data show that bradykinin can initiate the cascade of cytokine release that mediates hyperalgesic responses to carrageenin and endotoxin (1 microgram). The lack of effect of Hoe 140 on hyperalgesic responses to LPS (5 microgram) suggests that the release of hyperalgesic cytokines can be initiated independently of bradykinin BK2 receptors.

Bradykinin release of TNF-alpha plays a key role in the development of inflammatory hyperalgesia.

Using specific antisera for IL-1 beta and IL-8, as well as cyclooxygenase inhibitors and propranolol, we have demonstrated that these cytokines are responsible for the prostaglandin and sympathetic components of carrageenin-induced hyperalgesia in the rat paw test. The release of IL-1 beta and IL-8 is preceded by the liberation of TNF-alpha. We have also tested in a nociceptive model the effects of bradykinin and a specific bradykinin antagonist, HOE 140, on the hyperalgesia induced by carrageenin and lipopolysaccharide (LPS). Bradykinin-induced hyperalgesia was abolished by HOE 140 and by treatment of the paws with anti-TNF-alpha antisera. HOE 140 significantly inhibited the hyperalgesia induced by carrageenin and LPS. It is suggested that in these two models bradykinin is associated with the release of hyperalgesic cytokines.

The pivotal role of tumour necrosis factor alpha in the development of inflammatory hyperalgesia.

1. The hyperalgesic activities in rats of interleukin-1 beta (IL-1 beta), IL-6, IL-8, tumour necrosis factor alpha (TNF alpha) and carrageenin were investigated. 2. IL-6 activated the previously delineated IL-1/prostaglandin hyperalgesic pathway but not the IL-8/sympathetic mediated hyperalgesic pathway. 3. TNF alpha and carrageenin activated both pathways. 4. Antiserum neutralizing endogenous TNF alpha abolished the response to carrageenin whereas antisera neutralizing endogenous IL-1 beta, IL-6 and IL-8 each partially inhibited the response. 5. The combination of antisera neutralizing endogenous IL-1 beta + IL-8 or IL-6 + IL-8 abolished the response to carrageenin. 6. These results show that TNF alpha has an early and crucial role in the development of inflammatory hyperalgesia. 7. The delineation of the role of TNF alpha, IL-1 beta, IL-6 and IL-8 in the development of inflammatory hyperalgesia taken together with the finding that the production of these cytokines is inhibited by steroidal anti-inflammatory drugs provides a mechanism of action for these drugs in the treatment of inflammatory hyperalgesia.

Analgesia by direct antagonism of nociceptor sensitization involves the arginine-nitric oxide-cGMP pathway.

We tested the hypothesis that activation of the nitric oxide (NO)-cGMP pathway is involved in the mechanism of two directly acting non-opiate peripheral analgesics, myrcene and dipyrone, using our modification of the Randall-Selitto test. The NO inhibitor, NG-monomethyl-L-arginine (50 micrograms/paw) and methylene blue (500 micrograms/paw) abolished the analgesic effect of dipyrone and myrcene. Dibutyryl cyclic adenosine monophosphate (DbcAMP) caused a dose-dependent hyperalgesia (20, 50 and 100 micrograms/paw). Only responses to low doses of DbcAMP were inhibited by the two analgesics. Pretreatment with MY5445 (50 micrograms/paw) resulted in potentiation of the effects of both analgesics. These results support our hypothesis that the sensitivity of nociceptors may be controlled by the balance between the levels of cAMP and cGMP. Stimulation of the NO-cGMP pathway is probably the common denominator for the mode of action of peripheral analgesics which block hyperalgesia directly.

Blockade of hyperalgesia and neurogenic oedema by topical application of nitroglycerin.

Surprisingly, a single topical application of a nitroglycerin (NTG) gel in humans has been shown to cause analgesia and to reduce oedema in thrombophlebitis. In the present investigation, we showed that the NTG gel reduces prostaglandin E2-induced hyperalgesia and blocks neurogenic inflammation induced in rat skin by antidromic electrical stimulation of the saphenous nerve. These results offer an explanation for the effects of topical application of NTG observed in thrombophlebitis, which may be common to other cutaneous pathologies. The data also support the development of nitrates the effects of which are restricted to the site of application.

Peripheral analgesic activities of peptides related to alpha-melanocyte stimulating hormone and interleukin-1 beta 193-195.

1. The hyperalgesic effects of interleukin-1 beta (IL-1 beta) and prostaglandin E2 (PGE2) were measured in rats. 2. Hyperalgesic responses to IL-1 beta were inhibited in a dose-dependent manner by alpha-melanocyte stimulating hormone (alpha-MSH)-related peptides with the following order of potency: [N1(4),D-Phe7]alpha-MSH greater than alpha-MSH greater than Lys-D-Pro-Val greater than Lys-Pro-Val greater than Lys-D-Pro-Thr greater than D-Lys-Pro-Thr. 3. Hyperalgesic responses to PGE2 were not inhibited by Lys-D-Pro-Thr and D-Lys-Pro-Thr but were inhibited in a dose-dependent manner by the other peptides with the same order of potency as against IL-1 beta. 4. The potencies of [N1(4), D-Phe7]alpha-MSH and alpha-MSH were greatly diminished by deletion of their C-terminal tripeptide, Lys11-Pro-Val13. 5. Nor-binaltorphimine (Nor-BNI) largely reversed the analgesic effects of alpha-MSH, [N1(4), D-Phe7]alpha-MSH, Lys-Pro-Val and Lys-D-Pro-Val indicating that kappa-opioid receptors mediated the analgesic activity of these peptides. 6. Nor-BNI did not antagonize the inhibition by Lys-D-Pro-Thr and D-Lys-Pro-Thr of IL-1 beta evoked hyperalgesia indicating that these peptides were not acting via kappa-opioid receptors.

Interleukin-8 as a mediator of sympathetic pain.

1. The hyperalgesic effects of interleukin-8 (IL-8), interleukin-1 beta (IL-1 beta) and carrageenin were measured in a rat paw pressure test. 2. IL-8 evoked a dose-dependent hyperalgesia which was attenuated by a specific antiserum, the beta-adrenoceptor antagonists atenolol and propranolol, the dopamine receptor antagonist SCH 23390 and the adrenergic neurone-blocking agent guanethidine. The hyperalgesia was not attenuated by the cyclooxygenase inhibitor indomethacin or the IL-1 beta analogue Lys-D-Pro-Thr. 3. IL-1 beta-evoked hyperalgesia was attenuated by indomethacin and Lys-D-Pro-Thr but not by atenolol or SCH 23390. 4. Carrageenin-evoked hyperalgesia was attenuated by atenolol, indomethacin and anti-IL-8 serum. The effects of atenolol and anti-IL-8 serum were not additive. The effects of indomethacin and anti-IL-8 serum were additive: this combination abolished carrageenin-evoked hyperalgesia. 5. A new biological activity of IL-8 is described, namely the capacity to evoke hyperalgesia by a prostaglandin-independent mechanism. IL-8 is the first endogenous mediator to be identified as evoking hyperalgesia involving the sympathetic nervous system. Since IL-8 is released by activated macrophages and endothelial cells it may be a humoral link between tissue injury and sympathetic hyperalgesia.

Myrcene mimics the peripheral analgesic activity of lemongrass tea.

Oral administration of an infusion of lemongrass (Cymbopogon citratus) fresh leaves to rats produced a dose-dependent analgesia for the hyperalgesia induced by subplantar injections of either carrageenin or prostaglandin E2, but did not affect that induced by dibutyryl cyclic AMP. These results indicate a peripheral site of action which was confirmed with the essential oil obtained by steam distillation of the leaves. Silica gel column fractionation of the essential oil allowed the identification of myrcene as the major analgesic component in the oil. Identification of the components was made by thin-layer chromatography and checked by mass spectrometry. The peripheral analgesic effect of myrcene was confirmed by testing a standard commercial preparation on the hyperalgesia induced by prostaglandin in the rat paw test and upon the contortions induced by intraperitoneal injections of iloprost in mice. In contrast to the central analgesic effect of morphine, myrcene did not cause tolerance on repeated injection in rats. This analgesic activity supports the use of lemongrass tea as a "sedative" in folk medicine. Terpenes such as myrcene may constitute a lead for the development of new peripheral analgesics with a profile of action different from that of the aspirin-like drugs.