Vagal modulation of bradykinin-induced mechanical hyperalgesia in the female rat.

In male rats, activity in subdiaphragmatic vagal afferents modulates nociception via an adrenal medulla-dependent mechanism. Because both the vagus and adrenal medullae are sexually dimorphic, we evaluated vagotomy-induced changes in mechanical nociceptive threshold and inflammatory hyperalgesia in female rats and compared them to those previously reported in male rats. We have found that (1) mechanical nociceptive threshold is lower in female rats than in male rats, perhaps because of tonic release of adrenal medullary factors in female rats; (2) mechanical nociceptive threshold in female rats is influenced to a lesser degree by activity in the subdiaphragmatic vagus; (3) vagotomy-induced enhancement of bradykinin hyperalgesia is greater in female rats; (4) in female rats, in contrast to male rats, celiac plus celiac accessory branch vagotomy failed to fully account for the enhancement of bradykinin hyperalgesia in complete subdiaphragmatic vagotomy; and (5) in female rats, in contrast to male rats, adrenal medullectomy plus subdiaphragmatic vagotomy only partially (approximately 30%) reversed the effect of vagotomy on bradykinin hyperalgesia. These findings demonstrate sexual dimorphism in the modulation of both mechanical nociceptive threshold and bradykinin-induced hyperalgesia by activity in subdiaphragmatic vagal afferents as well as the adrenal medulla.     

Repeated sound stress enhances inflammatory pain in the rat

While it is well established that acute stress can produce antinociception, a phenomenon referred to as stress-induced analgesia, repeated exposure to stress can have the opposite effect. Since, chronic pain syndromes, such as fibromyalgia and rheumatoid arthritis, may be triggered and/or exacerbated by chronic stress, we have evaluated the effect of repeated stress on mechanical nociceptive threshold and inflammatory hyperalgesia. Using the Randall-Selitto paw pressure test to quantify nociceptive threshold in the rat, we found that repeated non-habituating sound stress enhanced the mechanical hyperalgesia induced by the potent inflammatory mediator, bradykinin, which, in normal rats, produces hyperalgesia indirectly by stimulating the release of prostaglandin E2 from sympathetic nerve terminals. Hyperalgesia induced by the direct-acting inflammatory mediator, prostaglandin E2 as well as the baseline nociceptive threshold, were not affected. Adrenal medullectomy or denervation, reversed the effect of sound stress. In sound stressed animals, bradykinin-hyperalgesia had a more rapid latency to onset and was no longer inhibited by sympathectomy, compatible with a direct effect of bradykinin on primary afferent nociceptors. In addition, implants of epinephrine restored bradykinin-hyperalgesia in sympathectomized non-stressed rats, lending further support to the suggestion that increased plasma levels of epinephrine can sensitize primary afferents to bradykinin. These results suggest that stress-induced enhancement of inflammatory hyperalgesia is associated with a change in mechanism by which bradykinin induces hyperalgesia, from being sympathetically mediated to being sympathetically independent. This sympathetic-independent enhancement of mechanical hyperalgesia is mediated by the stress-induced release of epinephrine from the adrenal medulla.     

Sympathectomy does not abolish bradykinin-induced cutaneous hyperalgesia in man.

Bradykinin is an endogenous peptide that is thought to be a chemical mediator of the hyperalgesia following inflammation. In rat, bradykinin has been postulated to cause hyperalgesia to mechanical stimuli by releasing prostaglandin from sympathetic post-ganglionic terminals. The aim of this study was to determine whether bradykinin-induced cutaneous hyperalgesia in humans requires post-ganglionic sympathetic terminals. In humans, intradermal injection of bradykinin produces dramatic hyperalgesia to heat but not mechanical stimuli. Therefore, we measured the magnitude and duration of pain and hyperalgesia to heat stimuli following intradermal injection of bradykinin into the leg of a woman before and 6 months after an ipsilateral, surgical, lumbar sympathectomy. The pain and hyperalgesia to heat following bradykinin was found to be unaffected by the sympathectomy. These results suggest that the algesic effects of cutaneous bradykinin in human are independent of the sympathetic nervous system.     

Gonadal hormones do not account for sexual dimorphism in vagal modulation of nociception in the rat

Subdiaphragmatic vagotomy produces a decrease in mechanical nociceptive threshold that is greater in male rats and an enhancement of bradykinin hyperalgesia that is greater in female rats. To examine the role of gonadal hormones in these sex differences, we evaluated the effect of gonadectomy, with or without gonadal hormone replacement, on vagal modulation of nociceptive threshold and bradykinin hyperalgesia by using the Randall-Selitto paw withdrawal test. Gonadectomy (before sexual maturation) plus vagotomy decreased nociceptive threshold in male rats more than either lesion alone, whereas neither lesion nor in combination had an effect on nociceptive threshold in female rats. Testosterone or dihydrotestosterone replacement in gonadectomized plus vagotomized males and 17β-estradiol in females did not significantly alter nociceptive threshold compared to vagotomy plus gonadectomy, respectively. Combined vagotomy and gonadectomy unexpectedly almost completely abolished bradykinin hyperalgesia, whereas gonadectomy alone had no effect on bradykinin hyperalgesia in both sexes. Testosterone replacement in vagotomized males and 17β-estradiol in vagotomized females reversed the effect of gonadectomy. Dihydrotestosterone replacement in vagotomized males also reversed the effect of gonadectomy on bradykinin hyperalgesia, although to a lesser degree than testosterone. We conclude that although gonadal hormones and other gonadal-dependent mechanisms influence nociception, they do not account for sexual dimorphism in vagal modulation of mechanical nociceptive threshold or bradykinin hyperalgesia.     

Second Messengers Mediating the Expression of Neuroplasticity in a Model of Chronic Pain in the Rat

Hyperalgesic priming is a model of the transition from acute to chronic pain, in which previous activation of cell surface receptors or direct activation of protein kinase C epsilon markedly prolongs mechanical hyperalgesia induced by pronociceptive cytokines. We recently demonstrated a role of peripheral protein translation, alpha-calmodulin-dependent protein kinase II (αCaMKII) activation, and the ryanodine receptor in the induction of hyperalgesic priming. In the present study, we tested if they also mediate the prolonged phase of prostaglandin E₂–induced hyperalgesia. We found that inhibition of αCaMKII and local protein translation eliminates the prolonged phase of prostaglandin E₂ hyperalgesia. Although priming induced by receptor agonists or direct activation of protein kinase C epsilon occurs in male but not female rats, activation of αCaMKII and the ryanodine receptor also produces priming in females. As in males, the prolonged phase of prostaglandin E₂–induced hyperalgesia in female rats is also protein kinase C epsilon–, αCaMKII-, and protein translation–dependent. In addition, in both male and female primed rats, the prolonged prostaglandin E₂–induced hyperalgesia was significantly attenuated by inhibition of MEK/ERK. On the basis of these data, we suggest that the mechanisms previously shown to be involved in the induction of the neuroplastic state of hyperalgesic priming also mediate the prolongation of hyperalgesia.PerspectivesThe data provided by this study suggest that direct intervention on specific targets may help to alleviate the expression of chronic hyperalgesic conditions.     

Lumbar Sympathectomy Attenuates Cold Allodynia But Not Mechanical Allodynia and Hyperalgesia in Rats With Spared Nerve Injury

In certain patients with neuropathic pain, the pain is dependent on activity in the sympathetic nervous system. To investigate whether the spared nerve injury model (SNI) produced by injury to the tibial and common peroneal nerves and leaving the sural nerve intact is a model for sympathetically maintained pain, we measured the effects of surgical sympathectomy on the resulting mechanical allodynia, mechanical hyperalgesia, and cold allodynia. Decreases of paw withdrawal thresholds to von Frey filament stimuli and increases in duration of paw withdrawal to pinprick or acetone stimuli were observed in the ipsilateral paw after SNI, compared with their pre-SNI baselines. Compared with sham surgery, surgical lumbar sympathectomy had no effect on the mechanical allodynia and mechanical hyperalgesia induced by SNI. However, the sympathectomy significantly attenuated the cold allodynia induced by SNI. These results suggest that the allodynia and hyperalgesia to mechanical stimuli in the SNI model is not sympathetically maintained. However, the sympathetic nervous system may be involved, in part, in the mechanisms of cold allodynia in the SNI model. PERSPECTIVE: The results of our study suggest that the SNI model is not an appropriate model of sympathetically maintained mechanical allodynia and hyperalgesia but may be useful to study the mechanisms of cold allodynia associated with sympathetically maintained pain states.     

Analysis of the antinociceptive effect of the flavonoid myricitrin: evidence for a role of the L-arginine-nitric oxide and protein kinase C pathways

The present study investigated the antinociceptive effects of the flavonoid myricitrin in chemical behavioral models of pain in mice and rats. Myricitrin given by i.p. or p.o. routes produced dose-related antinociception when assessed on acetic acid-induced visceral pain in mice. In addition, the i.p. administration of myricitrin exhibited significant inhibition of the neurogenic pain induced by intraplantar (i.pl.) injection of capsaicin. Like-wise, myricitrin given by i.p. route reduced the nociception produced by i.pl. injection of glutamate and phorbol myristate acetate (PMA). Western blot analysis revealed that myricitrin treatment fully prevented the protein kinase C (PKC) alpha and PKCepsilon activation by PMA in mice hind paws. Myricitrin given i.p. also inhibited the mechanical hyperalgesia induced by bradykinin, without affecting similar responses caused by epinephrine and prostaglandin E(2). The antinociception caused by myricitrin in the acetic acid test was significantly attenuated by i.p. treatment of mice with the nitric oxide precursor, L-arginine. In contrast, myricitrin antinociception was not affected by naloxone (opioid receptor antagonist) or neonatal pretreatment of mice with capsaicin and myricitrin antinociceptive effects is not related to muscle relaxant or sedative action. Together, these results indicate that myricitrin produces pronounced antinociception against chemical and mechanical models of pain in rodents. The mechanisms involved in their actions are not completely understood but seem to involve an interaction with nitric oxide-L-arginine and protein kinase C pathways.     

Gender and gonadal hormone effects on vagal modulation of tonic nociception.

We studied the influence of gender and gonadal hormones on modulation of tonic nociception exerted by vagal activity. In male rats, subdiaphragmatic vagotomy resulted in significantly reduced nociceptive behavior during phase 2 of the formalin test. Whereas gonadectomy alone had no effect, it completely eliminated the suppressive effect of subdiaphragmatic vagotomy; however, sex hormone replacement with either testosterone or dihydrotestosterone did not restore the ability of subdiaphragmatic vagotomy to suppress nociceptive behavior. These results suggest that, in males, a gonad-dependent but androgenic gonadal hormone-independent mechanism contributes to pronociceptive effects of vagal afferent activity. Although neither gonadectomy nor subdiaphragmatic vagotomy alone affected the response to formalin in females, gonadectomy plus vagotomy resulted in significantly reduced nociceptive behavior during phase 2. Reconstitution with 17 beta-estradiol implants in gonadectomized females not only prevented suppression of nociceptive behavior seen with gonadectomy plus vagotomy, but also led to increased nociceptive behavior in the interphase between phases 1 and 2. However, placement of 17 beta-estradiol implants in gonad-intact females had no effect on formalin-induced nociceptive behavior. The finding that estrogen produced an increase in nociceptive behavior in gonadectomized female rats after vagotomy but not in normal female rats (with intact gonads and subdiaphragmatic vagus) suggests that the interaction between estrogen and nociceptive afferent activity is suppressed by vagal function. In conclusion, a nonandrogenic action of testicular function in male rats and estrogen in females seems to influence the effect of vagal activity on formalin-induced nociceptive behavior.     

Mitochondrial electron transport in models of neuropathic and inflammatory pain

Although peripheral nerve function is strongly dependent on energy stores, the role of the mitochondrial electron transport chain, which drives ATP synthesis, in peripheral pain mechanisms, has not been examined. In models of HIV/AIDS therapy (dideoxycytidine), cancer chemotherapy (vincristine), and diabetes (streptozotocin)-induced neuropathy, inhibitors of mitochondrial electron transport chain complexes I, II, III, IV, and V significantly attenuated neuropathic pain-related behavior in rats. While inhibitors of all five complexes also attenuated tumor necrosis factor alpha-induced hyperalgesia, they had no effect on hyperalgesia induced by prostaglandin E2 and epinephrine. Two competitive inhibitors of ATP-dependent mechanisms, adenosine 5'-(beta,gamma-imido) triphosphate and P1,P4-di(adenosine-5') tetraphosphate, attenuated dideoxycytidine, vincristine, and streptozotocin-induced hyperalgesia. Neither of these inhibitors, however, affected tumor necrosis factor alpha, prostaglandin E2 or epinephrine hyperalgesia. These experiments demonstrate a role of the mitochondrial electron transport chain in neuropathic and some forms of inflammatory pain. The contribution of the mitochondrial electron transport chain in neuropathic pain is ATP dependent.     

Regulation and function of spinal and peripheral neuronal B1 bradykinin receptors in inflammatory mechanical hyperalgesia

Activation of either B1 or B2 bradykinin receptors by kinins released from damaged tissues contributes to the development and maintenance of inflammatory hyperalgesia. Whereas B2 agonists activate sensory neurones directly, B1 agonists were thought only to have indirect actions on sensory neurones. The recent discovery of constitutive B1 receptor expression in the rat nervous system lead us to re-investigate the role of neuronal B1 receptors in inflammatory hyperalgesia. Therefore we have examined B1 bradykinin receptor regulation in rat dorsal root ganglia in a model of inflammatory hyperalgesia, and correlated it with hyperalgesic behaviour. Twenty-four hours after injection of Freund's complete adjuvant into one hindpaw, there was a significant increase in B1 protein expression (measured by immunohistochemistry) in both ipsilateral and contralateral dorsal root ganglion neurones, whereas axotomy resulted in reduction of B1 protein in ipsilateral dorsal root ganglia. In behavioural experiments, the B1 antagonist desArg10HOE140, administered by either intrathecal or systemic routes, attenuated Freund's complete adjuvant-induced mechanical hyperalgesia in the inflamed paw, but did not affect mechanical allodynia. The B1 agonist, desArg9BK, did not affect paw withdrawal thresholds in nai;ve rats following intraplantar administration into the paw, whilst intrathecal administration elicited mechanical hyperalgesia. However, after Freund's complete adjuvant-induced inflammation, desArg9BK caused a marked mechanical hyperalgesia, by either route, of the contralateral, uninflamed hindpaw, correlating with the observed contralateral and ipsilateral increases in receptor levels. Our results suggest a functional role for B1 receptors expressed both in the periphery and in the spinal cord, in mechanical hyperalgesia during inflammation.     

Multiple PKCε-dependent mechanisms mediating mechanical hyperalgesia

We have recently implicated mitochondrial mechanisms in models of neuropathic and inflammatory pain, in some of which a role of protein kinase Cε (PKCε) has also been implicated. Since mitochondria contain several proteins that are targets of PKCε, we evaluated the role of mitochondrial mechanisms in mechanical hyperalgesia induced by proinflammatory cytokines that induce PKCε-dependent nociceptor sensitization, and by a direct activator of PKCε (ψεRACK), in the rat. Prostaglandin E₂ (PGE₂)-induced hyperalgesia is short lived in naïve rats, while it is prolonged in ψεRACK pre-treated rats, a phenomenon referred to as priming. Inhibitors of two closely related mitochondrial functions, electron transport (complexes I–V) and oxidative stress (reactive oxygen species), attenuated mechanical hyperalgesia induced by intradermal injection of ψεRACK. In marked contrast, in a PKCε-dependent form of mechanical hyperalgesia induced by prostaglandin E₂ (PGE₂), inhibitors of mitochondrial function failed to attenuate hyperalgesia. These studies support the suggestion that at least two downstream signaling pathways can mediate the hyperalgesia induced by activating PKCε.     

Ethanol withdrawal-associated allodynia and hyperalgesia: age-dependent regulation by protein kinase C epsilon and gamma isoenzymes.

Ethanol (EtOH) withdrawal increases sensitivity to painful stimuli in adult rats. In this study, withdrawal from a single, acute administration of EtOH dose-dependently produced mechanical allodynia and thermal hyperalgesia in postnatal day 7 (P7) rats. In contrast, P21 rats exhibited earlier and more prolonged mechanical allodynia but not thermal hyperalgesia. For both P7 and P21 rats, blood and spinal cord EtOH levels peaked at 30 minutes after administration, with P7 rats achieving overall higher spinal cord concentrations. Protein kinase C (PKC) has been implicated in mediating pain responses. Inhibitory PKC- and gamma-specific peptides attenuated mechanical allodynia and thermal hyperalgesia in P7 rats, whereas only the PKCgamma inhibitor prevented mechanical allodynia in P21 rats. Immunoreactive PKC in dorsal root ganglion and PKCgamma in lumbar spinal cord increased at 6 hours after EtOH administration in P7 rats. In P21 rats, the density of PKC immunoreactivity remained unchanged, whereas the density of PKCgamma immunoreactivity increased and translocation occurred. These studies demonstrate developmental differences in neonatal nociceptive responses after withdrawal from acute EtOH and implicate a role for specific PKC isozymes in EtOH withdrawal-associated allodynia and hyperalgesia. PERSPECTIVE: This study examines age-specific nociceptive responses after ethanol exposure by using 2 different ages of rats. The results suggest that ethanol age-dependently alters sensitivity to mechanical and thermal stimuli via specific protein kinase C isozymes. These results begin to ascertain the mechanisms that produce abnormal pain after alcohol exposure.     

Sympathoadrenal contribution to nicotinic and muscarinic modulation of bradykinin-induced plasma extravasation in the knee joint of the rat.

Previous results from this laboratory demonstrated that plasma extravasation produced by intra-articular infusion of bradykinin in the rat is mediated by an action on the sympathetic terminals in the knee joint and that adrenal medullary epinephrine regulates the plasma extravasation provoked by bradykinin. Because the release of epinephrine is under cholinergic control, we have now evaluated the effect of nicotinic and muscarinic cholinergic agonists on bradykinin-induced plasma extravasation in the knee joint of the rat. We report that s.c. administration of nicotine and carbachol attenuated plasma extravasation induced by bradykinin; this attenuation was significantly antagonized by systemic injection of hexamethonium and atropine, respectively. The nicotine and carbachol effects were also significantly attenuated after removal of the adrenal medulla. These results indicate that both nicotine and carbachol can inhibit bradykinin-induced plasma extravasation and that this inhibition is mediated, at least in part, through activation of nicotinic and muscarinic receptors in the adrenal medulla. Finally, local perfusion of the knee joint with hexamethonium did not affect the inhibition of bradykinin-induced plasma extravasation produced by systemic nicotine. Intra-articular perfusion of atropine potentiated the inhibition of bradykinin-induced plasma extravasation by systemic carbachol, indicating that muscarinic receptors in the synovium also contribute to plasma extravasation. The inhibitory action of nicotine on plasma extravasation may contribute, in part, to the reported increased severity of arthritis in individuals who smoke.     

Antinociceptive properties of mixture of alpha-amyrin and beta-amyrin triterpenes: evidence for participation of protein kinase C and protein kinase A pathways

The mixture of the two pentacyclic triterpenes alpha-amyrin and beta-amyrin, isolated from the resin of Protium kleinii and given by intraperitoneal (i.p.) or oral (p.o.) routes, caused dose-related and significant antinociception against the visceral pain in mice produced by i.p. injection of acetic acid. Moreover, i.p., p.o., intracerebroventricular (i.c.v.), or intrathecal (i.t.) administration of alpha,beta-amyrin inhibited both neurogenic and inflammatory phases of the overt nociception caused by intraplantar (i.pl.) injection of formalin. Likewise, alpha,beta-amyrin given by i.p., p.o., i.t., or i.c.v. routes inhibits the neurogenic nociception induced by capsaicin. Moreover, i.p. treatment with alpha,beta-amyrin was able to reduce the nociception produced by 8-bromo-cAMP (8-Br-cAMP) and by 12-O-tetradecanoylphorbol-13-acetate (TPA) or the hyperalgesia caused by glutamate. On the other hand, in contrast to morphine, alpha,beta-amyrin failed to cause analgesia in thermal models of pain. The antinociception caused by the mixture of compounds seems to involve mechanisms independent of opioid, alpha-adrenergic, serotoninergic, and nitrergic system mediation, since it was not affected by naloxone, prazosin, yohimbine, DL-p-chlorophenylalanine methyl ester, or L-arginine. Interestingly, the i.p. administration of alpha,beta-amyrin reduced the mechanical hyperalgesia produced by i.pl. injection of carrageenan, capsaicin, bradykinin, substance P, prostaglandin E2, 8-Br-cAMP, and TPA in rats. However, the mixture of compounds failed to alter the binding sites of [3H]bradykinin, [3H]resiniferatoxin, or [3H]glutamate in vitro. It is concluded that the mixture of triterpene alpha-amyrin and beta-amyrin produced consistent peripheral, spinal, and supraspinal antinociception in rodents, especially when assessed in inflammatory models of pain. The mechanisms involved in their action are not completely understood but seem to involve the inhibition of protein kinase A- and protein kinase C-sensitive pathways.     

The effect of spinal and systemic administration of indomethacin on zymosan-induced edema, mechanical hyperalgesia, and thermal hyperalgesia.

Pretreatment with intraperitoneal (i.p.) indomethacin was used to determine whether indomethacin preferentially affected the development of edema and hyperalgesia to thermal and mechanical stimuli produced by injection of zymosan in the ispsilateral hindpaw of the rat. Indomethacin also was delivered intrathecally (i.t.) either 30 minutes before or 4 hours after intraplantar zymosan to determine whether spinal prostaglandin production was important for the induction and/or maintenance of hyperalgesia. Zymosan alone produced a robust edema, a monophasic mechanical hyperalgesia, and a biphasic thermal hyperalgesia in the ipsilateral hindpaw. Systemic administration of indomethacin reduced zymosan-induced edema and increased thermal and mechanical response thresholds in the zymosan-injected paw. Systemic indomethacin did not affect thermal withdrawal response thresholds in the uninjected contralateral hindpaw of zymosan-treated rats, but significantly increased mechanical withdrawal thresholds of the uninjected contralateral paw of zymosan-treated rats. i.t. administration of indomethacin before the induction of hyperalgesia attenuated the development of zymosan-induced mechanical hyperalgesia, but did not affect the development of either zymosan-induced edema or thermal hyperalgesia. Once hyperalgesia was established, i.t. indomethacin also attenuated the mechanical hyperalgesia whereas it had no effect on thermal hyperalgesia or edema. These data suggest that peripheral, but not spinal prostaglandins contribute to the edema and development of thermal hyperalgesia produced by zymosan. In contrast, spinal prostaglandins contribute to the development and maintenance of mechanical hyperalgesia.     

Lumbar sympathectomy failed to reverse mechanical allodynia- and hyperalgesia-like behavior in rats with L5 spinal nerve injury

The L5 spinal nerve ligation model of neuropathic pain in rats has been proposed as a model for sympathetically maintained pain (SMP) based on the effects of surgical or chemical sympathectomy on nerve injury induced behavior. In an attempt to confirm that the lesion produces an animal model of SMP, surgical sympathectomies were independently conducted in two different laboratories (Johns Hopkins and University Kiel) using male Sprague-Dawley (n = 30) or Wistar rats (n = 14). The L5 spinal nerve was ligated or cut and ligated. Using von Frey hairs, paw withdrawal threshold and incidence of paw withdrawal were tested concurrently before and after the sympathectomy. The sympathectomy was either verified by (a) glyoxylic acid staining of peripheral blood vessels of the hindpaw or (b) skin temperature measurements of the hindpaws. To blind the experimenter, surgeries and behavioral tests were performed by two different investigators and a sham sympathectomy was performed at Johns Hopkins. Decreased paw withdrawal thresholds and increased frequencies of paw withdrawal on the lesioned side were observed after the L5 lesion. Thus, the L5 spinal nerve ligation resulted in behavioral signs of allodynia and hyperalgesia to mechanical stimuli. Lumbar surgical sympathectomy 1-3 weeks after the lesion or prior to lesion with bilateral removal of the sympathetic ganglia L2-L4, however, did not reverse or prevent the behavioral changes induced by the nerve injury. The lack of effect of the sympathectomies was independent of the testing paradigm used. Experiments in Wistar and Sprague-Dawley rats yielded the same results. Potential reasons for the discrepancies between the present study and earlier reports are discussed. These results indicate that an L5 spinal nerve injury rat model is not a reliable model for SMP.     

Metallopeptidase inhibition potentiates bradykinin-induced hyperalgesia

The neuropeptide bradykinin (BK) sensitizes nociceptor activation following its release in response to inflammatory injury. Thereafter, the bioactivity of bradykinin is controlled by the enzymatic activities of circulating peptidases. One such enzyme, the metalloendopeptidase EC3.4.24.15 (EP24.15), is co-expressed with bradykinin receptors in primary afferent neurons. In this study, using approaches encompassing pharmacology, biochemistry, cell biology, and behavioral animal models, we identified a crucial role for EP24.15 and the closely related EP24.16 in modulating bradykinin-mediated hyperalgesia. Pharmacological analyses indicated that EP24.15 and EP24.16 inhibition significantly enhances bradykinin type-2 receptor activation by bradykinin in primary trigeminal ganglia cultures. In addition, bradykinin-induced sensitization of TRPV1 activation was increased in the presence of the EP24.15/16 inhibitor JA-2. Furthermore, behavioral analyses illustrated a significant dose-response relationship between JA-2 and bradykinin-mediated thermal hyperalgesia. These results indicate an important physiological role for the metallopeptidases EP24.15 and EP24.16 in regulating bradykinin-mediated sensitization of primary afferent nociceptors.     

Muscle inflammation induces a protein kinase Cepsilon-dependent chronic-latent muscle pain.

Skeletal muscle injuries can induce chronic pain, but the underlying mechanism is unknown. One possible cause has been suggested to be an increased sensitivity to inflammatory mediators. We demonstrate that self-limited inflammatory hyperalgesia induced by intramuscular carrageenan (lasting approximately 5 days) results in a state of chronic-latent hyperalgesia, revealed by injection of prostaglandin E(2) (PGE(2)) 10 days after carrageenan at the same site. In carrageenan-pretreated muscle, PGE(2) produced hyperalgesia that was unattenuated even 14 days after injection, markedly longer than the 4-hour hyperalgesia induced by PGE(2) in naive rats. This chronic-latent hyperalgesia was reversed as well as prevented by spinal intrathecal injection of oligodeoxynucleotide antisense to protein kinase Cepsilon, a second messenger implicated in long-lasting plasticity in cutaneous nociceptors. PERSPECTIVE: We describe a novel experimental model for chronic muscle pain, produced by mild acute muscle inflammation, that has clinical significance since it has the potential to reveal cellular processes by which acute inflammation or muscle trauma underlies chronic muscle pain.     

Bradykinin-induced contraction is inhibited by tiaramide, an anti-inflammatory drug, with an inhibition of increase in intracellular free calcium

The mechanism of bradykinin-induced contraction in rabbit urinary detrusor was investigated using an anti-inflammatory drug, tiaramide. The contraction as well as prostaglandin (PG) E2 release induced by bradykinin was abolished by treatment with indomethacin, indicating that the contraction was mediated by PGs. The accumulation of inositol phosphates (IP) by bradykinin was partly inhibited by treatment with indomethacin, suggesting that part of the IP accumulation was due to PGs. Although the remaining accumulation of IPs induced by bradykinin in the presence of indomethacin should elicit contraction in smooth muscle cells, indomethacin abolished bradykinin-induced contraction. The dissociation between indomethacin-induced inhibition of IP accumulation and contraction induced by bradykinin might be explained by the existence of PG-generating cells in addition to smooth muscle cells. Bradykinin stimulates phospholipase C, which leads to an increase in intracellular free Ca++, activation of phospholipase A2 and release of PGs in the PG-generating cells. The released PGs act on smooth muscle cells to elicit contractions via phospholipase C activation and Ca++ mobilization. Tiaramide inhibited the PGE2 release and contraction induced by bradykinin by reducing the arachidonic acid release from membrane phospholipid but did not have a direct effect on cyclo-oxygenase. Tiaramide reduced IP accumulation induced by bradykinin to an extent similar to indomethacin. However, tiaramide had no effect on IP accumulation induced by PGE2, although it potently inhibited the contraction induced by PGE2, which elicits contractions without affecting phospholipase A2. The rise in intracellular free Ca++ induced by PGE2 as well as bradykinin was inhibited by tiaramide.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pharmacological modification of the edema produced by combined infusions of prostaglandin E1 and bradykinin in canine forelimbs

In dogs anesthetized with pentobarbital, 60 min local i.a. infusions of prostaglandin E1 (4 micrograms/min) together with bradykinin (10 micrograms base/min) into forelimbs perfused at a constant pump controlled flow rate produced decreases in perfusion pressure and very marked increases in lymph flow, lymph total protein concentration, total protein transport and weight (266 g). Pretreatment with indomethacin did not significantly reduce the very marked increases in these parameters produced by the combined prostaglandin E1-bradykinin infusions. Treatment with diphenhydramine completely prevented the increases in lymph flow, lymph total protein concentration, total protein transport, weight and vasodilation produced by infusions of histamine, but not those produced by infusions of prostaglandin E1 or bradykinin. Pretreatment with methylprednisolone prevented the increases in lymph flow, lymph total protein concentration, total protein transport and weight produced by infusions of prostaglandin E1, but not those produced by infusions of high doses of histamine or bradykinin. Treatment with either methylprednisolone or diphenhydramine significantly reduced the very marked increases in these parameters produced by combined infusions of prostaglandin E1 and bradykinin to levels produced by infusions of bradykinin alone. Vasopressin or isoproterenol treatment essentially prevented the very marked increases in lymph flow, lymph total protein concentration, total protein transport and weight produced by combined infusions of prostaglandin E1 and bradykinin. These data suggest that the potentiation of the bradykinin edema formation produced by prostaglandin E1 results from an endogenous release of histamine and that treatment with vasopressin or isoproterenol essentially prevents the development of edema produced by combined infusions of these autacoids. Moreover, the potentiation is not dependent on the vasodilator action of prostaglandin E1 as it may be demonstrated under constant controlled flow conditions.