Effects of systemic bicuculline or morphine on formalin-evoked pain-related behaviour and c-Fos expression in trigeminal nuclei after formalin injection into the lip or tongue in rats.

This study examined differences in nociceptive responses between lip and tongue. Formalin-induced pain-related behaviour and c-Fos expression in the trigeminal caudal nucleus (Vc) with/without systemic preadministration of a gamma-aminobutyric acid (GABA) type A receptor antagonist, bicuculline (2 mg/kg, i.p., 10 min before formalin injection) or a micro-opioid receptor agonist, morphine (3 mg/kg, i.p., 10 min before formalin injection) have been studied. Formalin injection into the upper lip induced an immediate pain-related behaviour, mostly face-rubbing behaviour, for 15 min (phase 1, mean +/- SEM/5 min, 81.2 +/- 30.1), followed by a more increased activity for 15 min (phase 2, 205.4 +/- 43.6) and a decline to baseline for next 15 min (phase 3, 63.9 +/- 28.0). Formalin injection into the tongue induced similar amount of pain-related behaviour at phase 1 (67.9 +/- 16.7), followed by similar activity at phase 2 (48.6 +/- 6.2), and lesser behaviour at phase 3 (20.4 +/- 7.6). The behaviour at phase 2 decreased following preadministration of bicuculline or morphine when formalin was injected into the lip (b, 62.5 +/- 14.5; m, 95.8 +/- 10.0) but not into the tongue (b, 31.0 +/- 9.2; m, 77.4 +/- 27.0). A considerable numbers of c-Fos-immunoreactive (IR) cells were induced in the caudal and inter-medio-lateral center of superficial layers of the Vc (VcI/II; mean +/- SEM/section = 225.8 +/- 12.9) and magnocellular zone of the Vc (VcIII/IV; 67.1 +/- 4.7) 2 h after formalin injection into the lip. Much smaller numbers of c-Fos-IR cells were induced in the rostral and dorso-medial one-fourth of the VcI/II (72.6 +/- 3.7) and VcIII/IV (55.6 +/- 6.6) after formalin injection into the tongue. Following preadministration with systemic bicuculline or morphine, the formalin-induced c-Fos-IR cells were decreased more in the VcI/II when formalin was injected into the lip (VcI/II, 102.4 +/- 8.0; VcIII/IV, 32.8 +/- 1.4) than into the tongue (VcI/II, 49.5 +/- 8.1; VcIII/IV, 31.7 +/- 5.3). These results show that the lip is more sensitive to formalin-induced noxious stimulation and regulated more through GABA(A) and micro-opioid receptors than the tongue.

Effect of morphine on the release of excitatory amino acids in the rat hind instep: Pain is modulated by the interaction between the peripheral opioid and glutamate systems.

Behavioral evidence supports a role for peripheral glutamate receptors in normal nociceptive transmission. In this study, we examined the release of the excitatory amino acids, glutamate and aspartate, in the s.c. perfusate of the rat hind instep by in vivo microdialysis. Antidromic stimulation of the sciatic nerve and noxious stimuli in the form of heat stimulation and local application of capsaicin cream (1%) to the instep caused an increase in excitatory amino acid release. This capsaicin-induced excitatory amino acid release was suppressed by pretreatment with capsaicin. Both systemic (10 mg/kg, i.v.) and local injections (10(-5) M in the perfusate) of morphine inhibited the increase in excitatory amino acid release evoked by local application of capsaicin cream to the instep. This inhibitory effect of morphine was antagonized by naloxone either given systemically (5 mg/kg, i.v.) or locally (10(-5) M). These results suggest that excitatory amino acids are released from small diameter afferent fibers by heat stimulation in the periphery or local application of capsaicin cream, and that activation of opioid receptors, present on the peripheral endings of small-diameter afferent fibers, can regulate noxious stimulus-induced excitatory amino acid release.

Involvement of GABAergic systems in manifestation of pharmacological activity of desipramine.

We have conducted this study to elucidate the influence of GABAergic systems on manifestation of pharmacological activity of desipramine using both pharmacological and electrophysiological methods. Desipramine (20 mg/kg, i.p.) significantly blocked the adjuvant-induced thermal hyperalgesia, which was facilitated by treatment with the GABA(A) antagonist picrotoxin (2 mg/kg, i.p.) or the GABA(B) antagonist saclofen (2 mg/kg, i.p.). This analgesic effect of desipramine was antagonized by post-treatment with picrotoxin or saclofen. However, none of these compounds showed any effect in normal animals without adjuvant-induced inflammation. In a slice preparation of the hippocampus, treatment with GABA (10(-5)-5 x 10(-4) M), baclofen (10(-5)-10(-4) M) or muscimol (10(-5)-10(-4) M) inhibited the field potential evoked in pyramidal neurons by Schaffer collateral stimulation. The inhibitory effect of GABA was facilitated by concurrent application of desipramine, carbamazepine or diazepam at a concentration of 5 x 10(-5)-2 x 10(-4) M. The rank of order of facilitation is: desipramine > carbamazepine > diazepam. Desipramine also enhanced the inhibitory effect of baclofen and muscimol. These results suggest that desipramine causes GABAergic systems to activate still more, and this phenomenon appears to be involved in manifestation of the pharmacological activity of desipramine such as antinociception.

Effects of intrathecal c-fos antisense oligodeoxynucleotide on adjuvant-induced thermal hyperalgesia.

We examined the effects of intrathecally preadministered injections of a phosphorothioate analog of c-fos antisense and mismatch oligodeoxynucleotides (ODNs) on the withdrawal latency to a thermal stimulus following unilateral injection of complete Freund's adjuvant (CFA) into the hind footpad of rats. Pretreatment with the c-fos antisense ODN significantly decreased the CFA-induced expression of c-Fos protein dose-dependently in ipsilateral laminae I/II (LI/II) of the dorsal horn (mean +/- SEM per section: 10 nM ODN, 43.9+/-1.3; 25 nM ODN, 19.4+/-4.1) compared with pretreatment with the mismatch ODN (63.6+/-2.9; 60.6+/-4.0) or saline (56.6+/-5.5). Animals pre-treated with 25 nM of the c-fos antisense ODN significantly increased the withdrawal latency to the noxious thermal stimulation (63.0-70.5%; compared with contralateral to the CFA injection) compared with animals pretreated with mismatch ODN (28.5-42.6%) or saline (26.4-45.3%) from 0 to 5 h after unilateral injection of CFA into the hind footpad. Pretreatment with 10 nM antisense ODN had a less significant effect. These results indicate that the expression of CFA-induced c-Fos in the dorsal horn might facilitate thermal nociception.

Influence of capsaicin cream in rats with peripheral neuropathy.

We investigated the effect of topical application of capsaicin cream on withdrawal latency in the hind foot of rat in response to radiant heat in an experimental model of neuropathic pain. A neuropathic state was induced by loose ligation of the sciatic nerve with chromic gut suture. A marked thermal hyperalgesia was observed in response to heat stimulus applied to the operated side from 3 days through 2 weeks, followed by a gradual return to the control level by 35 days after surgery. Capsaicin cream applied to both the bilateral hind instep and sole once a day for a continuous period of 2 weeks or 4 weeks alleviated thermal hyperalgesia in a dose-dependent manner. A remarkable effect was observed 2 weeks after the start of the application and this effect proved to be reversible. On the other hand, in sham-operated animals when capsaicin cream was applied once daily from day 7 after the sham operation, from 1 day through 3 weeks following capsaicin application, withdrawal latency of the sham-operated paws of the capsaicin-treated group was significantly increased as compared to that of the vehicle cream-treated group. The effects of antagonists of glutamate receptor and tachykinin receptors were investigated 7 days post surgery. Pretreatment with MK-801 (0.5 mg kg(-1), i.p.), but not with CNQX (0.5 mg kg(-1), i.p.), reversed the thermal hyperalgesia following nerve injury. Neither of RP67580 (1--10 mg kg(-1), i.p.) nor SR48968 (1--10 mg kg(-1), i.p.) had any effect on the withdrawal latency in the injured and non-injured hind paw. These results suggest that although the manifestation of effectiveness may be delayed by changes in networks of neurotransmitters related to the nociceptive pathways following nerve injury, longer-term repetitive application of capsaicin cream has a significant therapeutic effect on subjects with painful peripheral neuropathy.

Influence of serotonin receptor antagonists on substance P and serotonin release evoked by tooth pulp stimulation with electro-acupuncture in the trigeminal nucleus cudalis of the rabbit.

We studied the effect of NAN-190 (5-HT(1A) antagonist), ketanserin (5-HT(2) antagonist) and ICS 205-930 (5-HT(3) antagonist) on tooth pulp stimulation (TPS)-induced 5-HT release and substance P (SP) release in the superficial layers of the trigeminal nucleus caudalis (SpVc-I,II) in the presence or absence of electro-acupuncture (EAP). TPS slightly increased 5-HT release and significantly increased SP release. In combination with EAP, TPS-induced 5-HT release was remarkably enhanced, whereas SP release was significantly suppressed. Pretreatment with NAN-190 (3.5 mg/kg, i.v.) significantly enhanced the increase in TPS-induced 5-HT release in the presence of EAP. On the other hand, the increase of 5-HT release induced following TPS in the presence of EAP was inhibited by pretreatment with ketanserin (2.5 mg/kg, i.v.) and ICS 205-930 (1 mg/kg, i.v.). When NAN-190 was pre-treated in the animals combined TPS and EAP, the amount of SP release was significantly reduced compared with the absence of this drug. On the other hand, pretreatment with ketanserin and ICS 205-930 reversed the inhibitory effect of EAP on the TPS-generated SP release, especially ICS 205-930, which remarkably enhanced TPS-induced SP release compared with the absence of this drug. On the basis of the obtained results, we concluded that NAN-190 and ICS 205-930 act on EAP-induced analgesia positively and suppressively, respectively, by regulation of TPS-generated SP release through activation of their subtype receptors. On the other hand, ketanserin does not affect TPS-induced 5-HT release and SP release in the presence of EAP.

Influence of painful chronic neuropathy on neurogenic inflammation.

The effect of topical application of capsaicin cream on neurogenic inflammation was investigated in a neuropathic pain model in rat. The neuropathic state was induced by loose ligation of the sciatic nerve with a chromic gut suture. A marked thermal hyperalgesia was observed in response to heat stimulation applied to the operated side from 3 days through 2 weeks, followed by a gradual return to the control level 35 days after surgery. In sham-operated animals, topical application of capsaicin cream to both sides of the hind paw, the instep and sole, as well as antidromic stimulation of the sciatic nerve led to a significant increase in the amounts of Evans blue and substance P (SP) released into the perfusates. This stimulus-induced extravasation was significantly suppressed by pretreatment with RP67580, an NK1 antagonist. On day 7 after ligation, capsaicin- and antidromic stimulation-induced extravasation were significantly reduced. At this time, both amount of SP released immediately after application of capsaicin and during antidromic stimulation were almost similar to that in sham-operated rats, whereas the basal amount of SP release significantly increased in ligated animals. In particular a major release of SP was detected immediately after the start of the perfusion compared with that in sham-operated rats. Plasma extravasation evoked by SP (10(-4) M) applied to the subcutaneous perfusate was significantly less in ligated than in sham-operated rats. These results suggest that nerve injury with chronic pain may produce increase in basal SP release into the peripheral tissues, and then such enhanced SP release cause reduction of SP-induced extravasation.

Background levels of atmospheric mercury in Kagoshima City, and influence of mercury emission from Sakurajima Volcano, Southern Kyushu, Japan

Vapor phase mercury concentration was determined daily for 1 year (Jan. 1996-Jan. 1997) in order to present the levels of atmospheric mercury in Kagoshima City and to estimate the influence of mercury emission from Sakurajima Volcano, southern Kyushu, Japan. The atmospheric mercury was collected on a porous gold collector at Kagoshima University and was determined by cold vapor atomic absorption spectrometry; Kagoshima University of Kagoshima City is located approximately 11 km west of Sakurajima Volcano. The mercury concentration obtained was in the range 1.2-52.5 ng m(-3) (mean 10.8 ng m(-3), n = 169). The atmospheric concentration varied from season to season; the concentration was high in summer and lower in winter. A linear relation was obtained by plotting ln[Hg/ng m(-3)] vs. 1/T for the north, south and west winds with correlation coefficients of -0.76, -0.79 and -0.83, respectively, but no such dependency was found for the east wind (r = -0.035). When the wind is blowing from the east, Kagoshima City is on the leeward side of the volcano. The impact of the fumarolic activity of the volcano on ambient air in the city was evident in the disappearance of temperature dependency with the appearance of the east wind. Atmospheric mercury concentration except for the east wind was considered to be background levels of Kagoshima City. As background levels, 8.1 +/- 5.3 ng m(-3), 14.8 +/- 7.9 ng m(-3), 13.9 +/- 11.7 ng m(-3) and 4.4 +/- 1.6 ng m(-3) (mean +/- S.D.) were obtained for spring, summer, autumn and winter, respectively.

Mercury contamination in the Yatsushiro Sea, south-western Japan: spatial variations of mercury in sediment.

Mercury-contaminated effluent was discharged into Minamata Bay from a chemical plant over a 20-year period until 1965 (from 1958 to 1959, effluent was discharged into Minamata River), causing Minamata disease. In an effort to characterize the extent of the contamination in the Yatsushiro Sea, the vertical and horizontal distributions of mercury in sediment were investigated. Sediment was sampled at 62 locations in the southern part of the sea from 4 to 6 March 1996. In the lower layers of the long cores of sediment, the total amount of mercury was at a relatively uniform low concentration. We interpret these low values to represent the background concentration absent of anthropogenic influence. The background value thus estimated for the Yatsushiro Sea was 0.059 +/- 0.013 mg kg(-1) (mean +/- S.D., n = 51). The highest concentration in each sample ranged from 0.086 to 3.46 mg kg(-1) (mean, 0.57 mg kg(-1)). The higher values were obtained at stations near Minamata Bay and the Minamata River (the sources of the pollution). Concentrations decreased with distance from the source. An inspection of the vertical profiles of mercury concentration in cores suggested that the deposited mercury had not been fixed in sediment but had been transported, despite 30 years having past since the last discharge of contaminated effluent. At nine stations, extractable inorganic and organic mercury concentrations were determined differentially. Inorganic mercury is the predominant species in sediment and organic mercury comprising approximately 1% of the total.

Effects of topically applied capsaicin cream on neurogenic inflammation and thermal sensitivity in rats.

The effects of capsaicin cream on neurogenic inflammation and thermal nociceptive threshold were investigated in rats. Firstly, for topical application of capsaicin cream to hind paw, we shaped boots from dental cement to prevent the animals from licking off the drug. Capsaicin cream (1%) led to significant increases in the amounts of Evans blue and substance P (SP) released into the perfusate, and the former response was significantly suppressed by pretreatment with RP67580, an NK1-receptor antagonist, but not by treatment with an NK2-receptor antagonist. Subsequent electrical stimulation of the sciatic nerve resulted in a significant reduction in Evans blue and SP extravasation 24 h after topical application of capsaicin cream. On the other hand, when capsaicin cream was repeatedly applied to both hind paws once a day, withdrawal latency for noxious heat stimulation decreased after 24 h, and this thermal hyperalgesia was reversed 3 days later. These results suggest that capsaicin cream initially affects neurogenic inflammation mechanisms and then blocks the pain transmission mechanism.

Interaction between nitric oxide and substance P on heat-induced inflammation in rat paw.

To elucidate the interaction between nitric oxide (NO) and substance P (SP) in neurogenic inflammatory responses, we measured the change in the degree of Evans blue leakage and NO levels in perfusate from the subcutaneous space in the rat instep following noxious heat stimulation (47 degrees C for 30 min). Furthermore, the effects of drugs affecting nitric oxide synthase were examined. Noxious heat stimulation caused on an increase in NOx, or NO2- and NO3- into the perfusate in parallel with plasma extravasation. Nw-nitro-L-arginine methylester (L-NAME: 100 mg/kg once daily.) intraperitoneally (i.p.) given five times (chronic treatment) significantly suppressed the increase in Evans blue extravasation induced by heat stimulation, whereas acute treatments with L- and D-NAME (100 mg/kg once, i.p.) did not show any significant effect. NO release induced by heating also was significantly suppressed by chronic pretreatment with L-NAME, but not by acute treatment. SP (10(-5) M) applied into the perfusate caused a remarkable increase in the NOx release into the perfusate. Intra-arterial injection of RP67580 (1 mg/kg) on the perfused side, but not SR48968 (1 mg/kg), significantly attenuated the increases in Evans blue leakage and NOx release during heat stimulation. These results suggest that heat-induced SP release from the peripheral endings of small-diameter afferent fibers causes NO generation through NK-1R, and that this gas act to elicit or enhance inflammatory responses.

Effect of nitric oxide on substance P release from the peripheral endings of primary afferent neurons.

To elucidate the interaction between nitric oxide (NO) and substance P (SP) in neurogenic inflammatory responses, we studied the effect of drugs related to nitric oxide (NO) on the levels of Evans blue and SP released into perfusate from the subcutaneous space in the rat instep. Noxious heat stimulation (47 degrees C for 30 min) caused an increase in SP release in parallel with plasma extravagation. N(omega)-nitro-L-arginine methylester (L-NAME: 100 mg/kg, once daily) given intraperitoneally (i.p.) five times (chronic treatment) significantly suppressed the heat-evoked SP release and Evans blue leakage. FK409 (10(-4) M), which evokes a release of NO, applied locally caused a remarkable increase in the SP release into the perfusate. These results suggest that heat-induced NO generation causes SP release from the peripheral endings of small-diameter primary afferent neurons.

Serotonin receptor subtypes involved in modulation of electrical acupuncture.

We examined the effects of intravenous injection of several serotonin (5-HT) antagonists on the inhibitory action of electro-acupuncture (EAP) against the nociceptive responses in the trigeminal nucleus caudalis in rabbits. The inhibitory effect of EAP was suppressed by pindolol, methysergide and ICS 205-930, whereas NAN-190 and ketanserin amplified the EAP effect. These results suggest that 5-HT1, except 5-HT1A; 5-HT2, except 5-HT2A; and 5-HT3 receptors are positively involved in EAP-induced analgesia, whereas the activation of 5-HT1A and 5-HT2A receptors suppressively act on EAP-induced analgesia.

Involvement of nitric oxide in re-innvervation of rat molar tooth pulp following transection of the inferior alveolar nerve.

The aim of this study was to elucidate whether nitric oxide (NO) is involved in re-innervation of rat molar tooth pulp following transection of the inferior alveolar nerve. The inferior alveolar nerves (IAN) of rats were transected unilaterally under anesthesia with chloral hydrate. The animals received horseradish peroxidase (HRP) application to mandibular molar tooth pulps on both sides and were fixed by transvascular perfusion. The average number of labeled cells on each side of the trigeminal ganglion was not significantly different [101 +/- 11 (mean +/- S.E.M.; n = 6, left) and 89 +/- 11 (n = 6, right)]. With HRP application on postoperative day 3, the ratio of the number of labeled neurons in the transected vs. non-transected (contralateral) sides was 31.5 +/- 5.8% (n = 11). The i.p. administration of N(omega)-nitro-L-arginine methyl ester (L-NAME; 100 mg/kg, once a day for a period of 4 days), but not D-NAME, significantly decreased the ratio of the number of labeled neurons (10.1 +/- 7.0%, n = 10). L-Arginine (300 mg/kg, i.p., once a day for a period of 4 days) slightly increased the number of labeled neurons on the transected side. Clonidine (25 microg/kg, i.p., once a day for a period of 4 days) failed to exhibit any significant effect on nerve regeneration. In the trigeminal ganglion ipsilateral to the transected IAN on postoperative day 4, NADPH-diaphorase (NADPH-d)-positive neurons had significantly increased. On the other hand, no changes in NADPH-d were observed in the superficial layers of the subnucleus caudalis of the spinal trigeminal nucleus from where primary neurons innervating the mammalian tooth pulp project. These results suggest that NO is involved in several mechanisms related to neuronal regeneration.

Involvement of calcium-activated potassium channels in the inhibitory prejunctional effect of morphine on peripheral sensory nerves.

We examined the contribution of potassium channels to the inhibitory effect of morphine on the increase in substance P release and cutaneous blood flow evoked by antidromic stimulation of the sectioned sciatic nerve. Cutaneous blood flow in the instep of the rat hind paw was measured by the non-invasive technique of laser Doppler flowmetry. Antidromic stimulation of the sectioned sciatic nerve caused a biphasic flow response, an initial transient decrease followed by an increase and an increase in substance P release into the subcutaneous perfusate of the instep of the rat hind paw. Both the increases of substance P release and cutaneous blood flow evoked by antidromic stimulation of the sectioned sciatic nerve were significantly inhibited by intra-arterial (i.a.) infusion of morphine (30 mumol/kg). This inhibitory effect of morphine was antagonized by pretreatment with naloxone (2 mg/kg, i.p.) or potassium channels blockers such as tetraethylammonium (40 mg/kg, i.v.). apamin (0.5 mg/kg, i.v.) and charybdotoxin (0.12 mg/kg. i.v.) but not with cesium chloride (85 mg/kg, i.v.) and glibenclamide (25 mg/kg, i.v.). These results suggest that the calcium-activated potassium channels may be involved in the prejunctional inhibitory effects of morphine in the hind instep of rats.

Nitric oxide in the rat spinal cord in Freund's adjuvant-induced hyperalgesia.

To elucidate the involvement of nitric oxide in spinal nociceptive processing, the correlation of thermal withdrawal latency with nitric oxide synthase-stained neurons in the rat lumbar dorsal horn was analyzed after adjuvant-induced inflammation. From 4 hr through 5 days after subcutaneous injection of complete Freund's adjuvant into the hind paw, a marked thermal hyperalgesia was observed for heat stimulus applied to the affected region. NADPH-diaphorase- and nitric oxide synthase-positive neurons increased significantly in the superficial layers of the dorsal horn ipsilateral to the inflamed hind paw at day 3 of adjuvant-induced inflammation. No change in NADPH-diaphorase-positive neurons was observed at 1 hr and 1 day of adjuvant-induced inflammation. The intravenous administration of N omega-nitro-L-arginine methyl ester (L-NAME, 50 mg/kg), an inhibitor of nitric oxide synthase, significantly blocked the adjuvant-induced thermal hyperalgesia at day 3 of inflammation, but not at day 1; and it had no effect in non-inflamed rats. This anti-hyperalgesic effect of L-NAME at day 3 of inflammation was reversed by the prior administration of L-arginine (600 mg/kg, i.p.), a substrate of nitric oxide synthase. These data suggest that nitric oxide producing neurons in the spinal dorsal horn are involved in maintaining and facilitating the hyperalgesia associated with chronic nociception.

A possible involvement of monoaminergic and opioidergic systems in the analgesia induced by electro-acupuncture in rabbits.

To elucidate mechanisms involved in analgesia induced by effects of electro-acupuncture (EAP), effects of EAP on evoked potentials and release of substance P (SP) following tooth pulp stimulation (ST) in the superficial layers of the trigeminal nucleus caudalis (Vc-I-II) were studied in the rabbit. The potentials evoked by ST were composed of two main components with conduction velocity of ca. 30 m/sec (fast component) and ca. 12 m/sec (late component). The late component was significantly inhibited by morphine (10 mg/kg, i.v.) or CP-96,345 (5 mg/kg, i.v.), an SP antagonist. This inhibitory effect of morphine was antagonized by naloxone (1 mg/kg, i.v.) or methysergide (5 mg/kg, i.v.). In addition, the late component was significantly inhibited by EAP, which was observed in ca. 70% of the rabbits examined. This EAP-induced inhibitory effect was antagonized by naloxone (1 mg/kg, i.v.) or methysergide (5 mg/kg, i.v.), but not by prazosin (5 mg/kg, i.v.) and yohimbine (1 mg/kg, i.v.). The stimulus-evoked SP release was inhibited by EAP, which was significantly antagonized by pretreatment with naloxone (1 mg/kg, i.v.) or methysergide (5 mg/kg, i.v.). These results suggest that one of the mechanisms of analgesia induced by EAP is due to inhibition of the stimulus-evoked SP release in the Vc-I-II through activation of the descending serotonergic systems linking up with opioidergic systems.

Contribution of bradykinin to heat-induced substance P release in the hind instep of rats.

To investigate the possible contribution of the bradykinin (BK) system to heat-induced substance P (SP) release from the peripheral endings of primary afferent nerves, we used the high molecular weight (HMW) and low molecular weight (LMW) kininogen-deficient rat strain (Brown Norway-Katholiek, B/N-Ka) and the normal rat strain (Brown Norway-Kitasato, B/N-Ki). We found that immersion of the paw of B/N-Ki rats in water of 47 degrees C for 20 min led to significant increases of BK, SP and Evans blue extravasation in the s.c. perfusate, and that similar treatment resulted in significantly lower levels in B/N-Ka rats. Local application of BK (10(-4) M) to the s.c. perfusate and intra-arterial infusion of BK 10(-5) mol/kg) increased Evans blue extravasation and SP release evoked by heat stimulation, respectively, in B/N-Ka rats to similar levels to those in B/N-Ki rats after heat-stimulation without BK treatment. These results indicate that BK released into the extravascular space by noxious stimulation is involved in SP release from the peripheral endings of capsaicin-sensitive primary sensory neurons.

[Releases of bradykinin and substance P by heating hind paw of rat].

Contribution of kallikrein-kinin system to heat-induced substance P (SP) release into the periphery was studied by using plasma kininogens-deficient strain Brown Norway Katholiek (B/N-Ka) and normal strain Brown Norway Kitasato (B/N-Ki) rats. Bradykinin (BK) and SP levels in the sc perfusates of the hind instep were measured by radioimmunoassay. In B/N-Ki rat, immersion of hind paw into hot water (47 degrees C) for 20 min led to an increase of BK (43 +/- s 34 fmol.min-1) and SP (11.1 +/- 9.7 fmol.min-1) in the perfusate, whereas those in B/N-Ka rat (BK 1.3 +/- 1.0 fmol.min-1 (P < 0.01), SP 5.5 +/- 3.5 fmol.min-1 (P < 0.05)) were remarkably less. Heat-induced extravasation (leakage of Evans blue) in B/N-Ka rat was also less than that in B/N-Ki rat (P < 0.05). Results suggest that kallikrein-kinin system is involved in the release of SP into the periphery, ie, BK released into the extravascular space by noxious heat stimulation intervenes in SP release.