BK-induced Plasma Extravasation Research Articles

Receptor mediation and nociceptin inhibition of bradykinin-induced plasma extravasation in the knee joint of the rat

Objective and designThe aim was to investigate the signaling mechanisms and regulation of bradykinin (BK)-induced inflammation in rat knee joint.Materials and methodsKnee joints of anesthetized rats were perfused with BK (0.1–1.0 μM), and synovial plasma extravasation (PE) was evaluated by spectrophotometrical measurement of Evans Blue leakage. To examine the signaling pathway, B1 antagonist [des-Arg10]-HOE140 (0.1–1.0 μM) and B2 antagonist HOE140 (0.05–1.0 μM), calcitonin gene-related peptide (CGRP) antagonist CGRP8-37 (0.5–1.0 μM), prostaglandin E2 antagonist AH-6809 (0.1–1.0 μM), and histamine H1 antagonist mepyramine (0.1–1.0 μM) were used. Nociceptin (0.0001–1.0 μM) and antagonist J-113397 were tested for modulation of BK-induced PE. The analyses were compared side-by-side with 5-hydroxytryptamine-induced PE.ResultsBK perfusion dose-dependently induced PE, which was blocked by HOE140, CGRP8-37, AH-6809, and mepyramine. It was also inhibited by nociceptin, which could be reversed by antagonist J-113397. In contrast, 5-hydroxytryptamine-induced PE was biphasically regulated by nociceptin and was not antagonized by CGRP8-37.ConclusionsBK-induced PE is mediated by B2 receptors and may involve CGRP, prostaglandin, and histamine pathways. BK-induced PE is inhibited by nociceptin through the activation of ORL1 receptors. There are differences between BK- and 5-hydroxytryptamine-induced inflammation in signaling and modulation.

Role of adrenal medulla in development of sexual dimorphism in inflammation.

Many inflammatory diseases show a female predilection in adults, but not prepubertally. Because sex differences in the inflammatory response in the adult rat are mediated, in part, by sexual dimorphism in adrenal medullary function, we investigated the contribution of the adrenal medulla to the ontogeny of sexual dimorphism in inflammation. Whilst there was no sex difference in the magnitude of the plasma extravasation (PE) induced by the potent inflammatory mediator bradykinin (BK) in prepubertal rats, in adult rats BK-induced PE was markedly greater in males. Also, adult male rats, gonadectomized prior to puberty, had a lower magnitude of BK-induced PE than did adult male controls, whilst adult females gonadectomized prepubertally had higher BK-induced PE than did controls. In rats gonadectomized after puberty, the magnitude of BK-induced PE in adult males was not affected, whilst in females it resulted in significantly higher BK-induced PE, similar to the effect of prepubertal gonadectomy. When tested prepubertally, adrenal denervation increased the magnitude of BK-induced PE in females, but not in males. In contrast, in both males and females tested as adults, but castrated prepubertally, and in gonad-intact adult females, adrenal denervation significantly increased the magnitude of BK-induced PE. Adrenal denervation in prepubertal females given adult levels of 17beta-oestradiol produced a marked enhancement in the denervation-induced increase in magnitude of BK-induced PE compared to females not exposed prematurely to sex hormones. These studies suggest that an adrenal medulla-dependent inhibition of BK-induced PE is present in female but not male rats, and is enhanced by oestrogen but suppressed by testosterone.

Spino-bulbo-spinal pathway mediating vagal modulation of nociceptive-neuroendocrine control of inflammation in the rat.

Stimulation of nociceptors by intradermal capsaicin produces depression of bradykinin (BK)-induced synovial plasma extravasation (PE) that is markedly enhanced by subdiaphragmatic vagotomy. This depression is mediated by the adrenal medullae, a propriospinal pathway between the afferent nociceptive input and preganglionic neurones projecting to the adrenal medullae, and a spino-bulbo-spinal pathway. Here we investigated the role of spinal ascending and descending pathways in the interaction between noxious and vagal afferent inputs, leading to inhibition of BK-induced PE mediated by the adrenal medullae. Nociceptors in the paw were activated by capsaicin and depression of BK-induced PE was measured in rats with intact or cut subdiaphragmatic vagus nerves. After cutting the dorsolateral funiculus (DLF) contralateral to the stimulated hindpaw (segmental level C5/C6 and T8/T9), depression of BK-induced PE was weak or absent both in rats with intact vagus nerves and in vagotomised rats, suggesting that an ascending excitatory pathway was interrupted. After cutting the DLF ipsilateral to the stimulated hindpaw, depression of BK-induced PE was already markedly enhanced, even in the absence of vagotomy. Ipsilateral DLF lesion (L2/L3) below the level of the spinal output to the adrenal medullae produced the same effect, suggesting interruption of a descending inhibitory pathway that relays the effect of vagal activity to the level of the capsaicin-induced nociceptive input. Contralateral and ipsilateral hemisection of the spinal cord (C5/C6) produced the same changes as the corresponding DLF lesions. Ipsi- or contralateral lesion of the dorsal funiculus at the spinal level T8/T9 had no effect on depression of BK-induced PE generated by cutaneous noxious stimulation of the forepaw. We suggest that noxious stimulation activates an ascending pathway of the spino-bulbo-spinal excitatory circuit which projects through the DLF contralateral to the nociceptive input, and that the inhibitory pathway which is activated by vagal afferent activity projects through the DLF ipsilateral to the nociceptive input.

Sex Steroid Regulation of the Inflammatory Response: Sympathoadrenal Dependence in the Female Rat

To investigate the role of sex steroids in sex differences in the response of rats to the potent inflammatory mediator bradykinin (BK), we evaluated the effect of sex steroid manipulation on the magnitude of BK-induced synovial plasma extravasation (PE). The magnitude of BK-induced PE is markedly less in females. Ovariectomy of female rats increased BK-induced PE, and administration of 17beta-estradiol to ovariectomized female rats reconstituted the female phenotype. Castration in male rats decreased BK-induced PE, and administration of testosterone or its nonmetabolizable analog dihydrotestosterone reconstituted the male phenotype. The results of these experiments strongly support the role of both male and female sex steroids in sex differences in the inflammatory response. Because the stress axes are sexually dimorphic and are important in the regulation of the inflammatory response, we evaluated the contribution of the hypothalamic-pituitary-adrenal and the sympathoadrenal axes to sex differences in BK-induced PE. Neither hypophysectomy nor inhibition of corticosteroid synthesis affected BK-induced PE in female or male rats. Adrenal denervation in females produced the same magnitude increase in BK-induced PE as adrenalectomy or ovariectomy, suggesting that the adrenal medullary factor(s) in females may account for the female sex steroid effect on BK-induced PE. Furthermore, we have demonstrated that in female but not male rats, estrogen receptor alpha immunoreactivity is present on medullary but not cortical cells in the adrenal gland. These data suggest that regulation of the inflammatory response by female sex steroids is strongly dependent on the sympathoadrenal axis, possibly by its action on estrogen receptors on adrenal medullary cells.

Annexin I is a local mediator in neural-endocrine feedback control of inflammation.

Annexin I is a local mediator in neural-endocrine feedback control of inflammation. J. Neurophysiol. 80: 3120-3126, 1998. Activation of primary afferent nociceptors induces a neural endocrine-mediated inhibition of the inflammatory response via a circuit that includes ascending spinal pathways and activation of the hypothalamic-pituitary adrenal (HPA) axis. This circuit inhibits sympathetic neuron-dependent plasma extravasation (PE) in the rat knee joint produced by bradykinin (BK), but not sympathetic neuron-independent PE produced by platelet activating factor (PAF). Noxious (25 mA) but not non-noxious (2.5 mA) electrical stimulation significantly increased plasma corticosterone concentrations, and intravenous infusion of corticosterone (5 micrograms/min) mimicked inhibition of BK-induced PE produced by noxious stimulation. However, perfusion of corticosterone locally through the knee joint, at doses that do not have a systemic action (i.e., </=1 microM), did not inhibit BK-induced PE. Annexin I (lipocortin-1), a 37-kDa member of a family of phospholipid and calcium binding proteins, can mediate local anti-inflammatory effects of glucocorticoids via a mechanism that is partially dependent on inhibition of phospholipase A2 activity and adhesion and transmigration of polymorphonuclear leukocytes. Because BK-induced PE is dependent on both polymorphonuclear leukocytes and phospholipase A2 activity, we tested the hypothesis that the action of corticosterone to inhibit BK-induced PE is mediated by stimulating the production and release of annexin I. Perfusion of BK (150 nM) through the rat knee joint induces a rapid and sustained increase in PE. Co-perfusion of BK with annexin I (100 ng/ml) through the knee joint mimics the inhibition of BK-induced PE produced by noxious electrical stimulation or by intravenous corticosterone. Co-perfusion of BK with annexin I antibody (LCPS1, 1:60 dilution) prevented the inhibition of BK-induced PE produced by noxious electrical stimulation or intravenous corticosterone adminstration. PAF-induced PE, which is not dependent on polymorphonuclear leukocytes, was not inhibited by local perfusion of annexin I. These data suggest that the inhibitory effect of C-fiber activity on BK-induced PE, acting via an HPA circuit, is mediated by annexin I in the knee joint.

Endocrine and vagal controls of sympathetically dependent neurogenic inflammation.

Recently the very significant role of the postganglionic sympathetic neuron (PGSN) terminal in the production of neurogenic inflammation has been appreciated. An important model of this sympathetically dependent inflammation is venular plasma extravasation (PE) and neutrophil attraction produced by local intra-articular injection of the potent inflammatory mediator bradykinin (BK). Sympathetic-dependent PE in the synovium has been proposed as a protective mechanism in arthritis. In a recent series of studies, a novel mechanism has been discovered by which activation of primary afferent nociceptors exerts a potent feedback inhibition of PGSN-dependent PE. Activation of nociceptive afferents was shown to be involved in this feedback system. Such a negative feedback control of the acute inflammatory response would have survival value; the inflammatory response, as initiated by a high degree of positive feedback, and the inflammatory process itself when persisting can result in significant tissue injury. If indeed HPA axis activity plays a significant physiological role in the modulation of neurogenic inflammation, then physiological processes that modulate the HPA axis would be expected to influence neurogenic inflammation. A dramatic effect of this kind has been demonstrated, in the rat, for vagal afferent activity. In the presence of subdiaphragmatic (or celiac branch) vagotomy, the potency of nociceptive afferent activity to inhibit sympathetically dependent, BK-induced PE was increased by four orders of magnitude compared to vagus-intact animal. Hypoactivity or hyperactivity of these vagally mediated mechanisms could contribute to diseases characterized by either an inadequate or an exaggerated inflammatory response.

Negative Feedback Neuroendocrine Control of Inflammatory Response in the Rat is Dependent on the Sympathetic Postganglionic Neuron

Negative feedback control of inflammation is mediated by activation of nociceptive afferents that in turn activates the hypothalamic-pituitary-adrenal axis to release corticosteroids. Plasma extravasation (PE) produced by the potent inflammatory mediator, bradykinin (BK), but not that induced by another potent inflammatory mediator, platelet-activating factor (PAF), is inhibited by released corticosterone. Because bradykinin, but not PAF, produces PE by a mechanism that is, in part, dependent on the sympathetic postganglionic neuron (SPGN) terminal, we tested the hypothesis that the negative feedback control of inflammation is dependent on the SPGN terminal in the inflamed tissue. In sympathectomized rats, the residual (i.e., SPGN-independent) PE in the knee joint produced by BK was not inhibited by noxious electrical stimulation. Furthermore, intravenous administration of corticosterone potently inhibited, with a similar time-course, the SPGN-dependent, but not the SPGN-independent, component of BK-induced PE. Neither electrical stimulation nor corticosterone inhibited PAF-induced PE. Finally, corticosterone's actions do not appear to be mediated by release of norepinephrine from the SPGN terminal, because neither the alpha-adrenergic receptor antagonist phentolamine nor the beta2-adrenergic receptor antagonist ICI 118, 551 antagonized the inhibition of BK-induced PE by corticosterone. We conclude that in the rat knee joint, negative feedback control of the inflammatory response is dependent on the presence of the SPGN terminal. Further, our data suggest that a significant component of corticosteroid-induced inhibition of PE produced by inflammatory mediators is SPGN-dependent.

Contribution of adrenal hormones to nicotine-induced inhibition of synovial plasma extravasation in the rat.

1. In this study, we examined the mechanism(s) by which s.c. nicotine inhibits synovial plasma extravasation. We found that nicotine dose-dependently inhibited bradykinin (BK)- and platelet activating factor (PAF)-induced plasma extravasation. 2. The effect of nicotine on both BK- and PAF-induced plasma extravasation was attenuated by adrenal medullectomy. ICI-118,551 (a selective beta 2-adrenoceptor blocker) (30 micrograms ml-1, intra-articularly) significantly attenuated the inhibitory action of high-dose (1 mg kg-1) nicotine on BK-induced plasma extravasation without affecting the inhibition by low- (0.01 microgram kg-1) dose nicotine or that on PAF-induced plasma extravasation by nicotine at any dose. This suggested that beta 2-adrenoceptors mediate the inhibitory actions of high-dose, but not low-dose, nicotine. We also found that systemic naloxone (an opioid receptor antagonist) (two hourly injections of 1 mg kg-1, i.p.) attenuated the inhibitory action produced by all doses of nicotine on BK- or PAF-induced plasma extravasation, suggesting the contribution of endogenous opioids. 3. RU-38,486 (a glucocorticoid receptor antagonist) (30 mg kg-1, s.c.), and metyrapone (a glucocorticoid synthesis inhibitor) (two hourly injections of 100 mg kg-1, i.p.) both attenuated the action of high-dose nicotine without affecting that of low-dose nicotine. 4. Spinal mecamylamine (a nicotinic receptor antagonist) (0.025 mg kg-1, intrathecally, i.t.) attenuated the action of high-dose, but not low-dose, nicotine, suggesting that part of the action of high-dose nicotine is mediated by spinal nicotinic receptors. 5. Combined treatment with ICI-118,551, naloxone and RU-38,486 attenuated the action of low-dose nicotine by an amount similar to that produced by naloxone alone but produced significantly greater attenuation of the effect of high-dose nicotine when compared to the action of any of the three antagonists alone.

Inhibition of bradykinin-induced synovial plasma extravasation produced by intrathecal nicotine is mediated by the hypothalamopituitary adrenal axis.

1. Bradykinin (BK)-induced plasma extravasation (PE) in the rat knee joint, which is dependent to a large extent on the sympathetic innervation of the synovium, is powerfully inhibited, dose dependently, by intrathecal administration of nicotine, especially after interruption of the impulse traffic in afferents of the abdominal vagus nerve. In this study we investigated in vagotomized animals possible efferent pathways that might mediate the inhibition produced by the intrathecally applied nicotine. We studied the role of the sympathetic supply to the knee joint, of the sympathoadrenal system, and of the hypothalamopituitary-adrenal (HPA) axis in the ability of intrathecal nicotine to inhibit BK-induced PE in the knee joint. The experimental interventions performed were as follows: recording activity in the lumbar sympathetic trunk; antagonizing the effect of epinephrine, released from the adrenal medulla; acute interruption of the lumbar sympathetic trunks; hypophysectomy; and blockade of the glucocorticoid receptors. We employed acutely vagotomized animals because in these animals nicotine-induced inhibition is enhanced. 2. We found that hypophysectomy or blockade of the glucocorticoid receptors markedly attenuated the inhibition of BK-induced PE produced by intrathecal nicotine. 3. Intrathecal nicotine did not affect activity in the sympathetic chain. 4. Acute interruption of the lumbar sympathetic chain, which leaves the sympathetic terminals in the synovium intact but abolishes activity in the sympathetic postganglionic neurons, did not change the inhibition of BK-induced PE produced by intrathecal nicotine. 5. Blockade of the beta 2 adrenoceptors in the knee joint, preventing in this way potential effects of epinephrine released by the adrenal medulla, did not affect the inhibition of BK-induced PE produced by intrathecal nicotine. 6. The results of the present experiments strongly support the hypothesis that the powerful suppression of BK-induced PE in the knee joint generated by intrathecal nicotine is mediated via the HPA axis and not via activity in sympathetic neurons innervating the knee joint or the adrenal medulla. Future studies are needed to determine in which functional contexts this pathway is active in the control of PE in the synovia and of other aspects of inflammation.

Mechanism of bradykinin-induced plasma extravasation in the rat knee joint.

1. We have investigated the mechanism of bradykinin (BK)-induced plasma extravasation into the knee joint of the anaesthetized rat. Accumulation of [125I]-human serum albumin within the synovial cavity was used as a marker of increased vascular permeability. 2. Perfusion with BK (1 microM) produced significant plasma extravasation into the knee which was inhibited by co-perfusion of the selective bradykinin B2 receptor antagonist D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]-bradykinin (Hoe 140, 200 nM). 3. The bradykinin B1 receptor agonist, [des-Arg9]-BK (up to 100 mM), did not induce plasma extravasation into the knee joint, over this time period. 4. Chemical sympathectomy by chronically administered 6-hydroxydopamine (6-OHDA) did not inhibit bradykinin-induced plasma extravasation. Acute intra-articular perfusion with 6-OHDA (to stimulate transmitter release from sympathetic nerve terminals) at concentrations up to 50 mM did not induce significant plasma extravasation. Intra-articular perfusion of 100 mM 6-OHDA induced significant plasma extravasation but produced severe systemic toxicity. 5. The selective neurokinin1 (NK1) receptor antagonist, RP67580 (230 nmol kg-1), or receptor antagonists for the mast cell products histamine and 5-hydroxytryptamine did not significantly inhibit BK-induced plasma extravasation. 6. Co-perfusion of the NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME) (1 mM) did not significantly inhibit the response to BK. 133Xe clearance from L-NAME (1 mM)-injected joints was significantly (P < 0.05) reduced compared to D-NAME injected joints, suggesting a reduction in blood flow as a result of decreased basal NO production. Systemic administration of L-NAME at doses sufficient to produce significant and sustained elevation of blood pressure (5 or 30 mg kg-1, i.v. 15 min prior to BK perfusion) also failed to significantly inhibit the BK-induced response.7 We conclude that, in normal joints, BK induces plasma extravasation by acting on bradykinin B2 receptors and that this response is not dependent on secondary release of mediators from sympathetic nerve terminals, sensory nerves, mast cells or on generation of NO.

Negative feedback neuroendocrine control of the inflammatory response in rats

We describe that an ongoing inflammatory response at one site (produced by complete Freund's adjuvant injection in the hindpaw) produces a negative feedback inhibition on plasma extravasation, produced by perfusion of the inflammatory mediator, bradykinin (160 nM), at a second site (the knee joint). This negative feedback process is abolished in rats that have been neonatally treated with capsaicin to deplete most of their unmyelinated primary afferent fibers, which suggests that this negative feedback process is mediated by activation of primary afferent fibers. Electrical stimulation of the hindpaw at intensities that excite C-fibers also inhibited bradykinin-induced plasma extravasation. Stimulation at intensities that only excite A-fibers had no effect on bradykinin-induced plasma extravasation. Platelet activating factor-induced plasma extravasation, which is not dependent on the innervation of the joint, was not inhibited by stimulation of C-fibers from the hindpaw. Acute surgical interruption of the lumbar sympathetic outflow to the hind limb (the paravertebral ganglia between L2 and L4) did not attenuate the depression of bradykinin-induced plasma extravasation produced by C-fiber stimulation. This indicates that the depression is not mediated by activity in the sympathetic outflow. Transection of the spinal cord, hypophysectomy, inhibition of corticosterone synthesis, and adrenalectomy (but not adrenal medullectomy) all prevented the inhibition of BK-induced plasma extravasation by electrical simulation, indicating that the negative feedback inhibition on plasma extravasation is dependent on an intact neuraxis and an intact hypothalamic-pituitary-adrenocortical axis. In summary, our data demonstrate a negative feedback inhibition of an inflammatory process, which is elicited by stimulation of C-fiber afferents.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of bradykinin B1 receptors in the maintenance of intra‐articular plasma extravasation in chronic antigen‐induced arthritis

1. The role of bradykinin B1 and B2 receptors in bradykinin- and des-Arg9-bradykinin-induced plasma extravasation in normal and inflamed rat knee joints was investigated by use of an antigen-induced model of chronic arthritis. A modification of an Evans blue extraction technique allowed the unstimulated (basal) plasma extravasation to be assessed in this model. The contributions of bradykinin B1 and B2 receptors towards basal synovial plasma extravasation were determined. 2. In normal knees, intra-articular injection of bradykinin (BK) induced plasma extravasation in a potent, dose-dependent manner with a threshold of 0.01 nmol and an ED50 of 0.1 nmol. In day 5 arthritic knees, basal plasma extravasation was substantially enhanced. Lower doses of BK had no demonstrable effect and increases above basal extravasation were first observed at 0.1 nmol. Thereafter the dose-response mirrored the response in normal knees and the maximal response was unaltered. 3. The B1 agonist, des-Arg9-BK, induced slight but significant plasma extravasation in normal knees but was less potent than bradykinin. This response was inhibited by the B1 receptor antagonist, des-Arg9, [Leu8]-BK. Lower doses of des-Arg9-BK bradykinin did not significantly increase basal extravasation in day 5 arthritic knees but, in contrast to BK, the maximal response was significantly enhanced. 4. The B2 antagonist, Hoe 140, inhibited BK-induced plasma extravasation in normal joints over a dose-range of 0.1-1.0 nmol but was relatively inactive in day 5 inflamed knees. The B1 receptor antagonist, des-Arg9, [Leu8]-BK, was relatively inactive in normal joints but showed increased potency against BK-induced plasma extravasation in day 5 arthritic joints.5. Hoe 140 and des-Arg9,[Leu8]-BK both inhibited basal extravasation in arthritic joints on days 1 and 5 post-challenge in a dose-dependent fashion. Whilst Hoe 140 was the more potent inhibitor on day 1, it was less potent than des-Arg9,[Leu8]-BK on day 5.6. Although the majority of responses to BK in normal tissue are mediated via B2 receptors, a small population of B1 receptors may exist in normal joint tissues. The data presented in this study suggest an evolving role for B1 receptors in the mediation of plasma extravasation in inflamed joint tissues. A role for BK antagonists in the treatment of arthritis is also suggested.

Sympathetic neuron factors involved in bradykinin-induced plasma extravasation in the rat

Previous studies have demonstrated that bradykinin (BK) produces a sympathetically dependent plasma extravasation into the rat knee joint which is, in part, dependent upon the production of a prostaglandin. In the present study, co-administration of the specific prostaglandin, PGE 2, markedly enhanced the BK-induced plasma extravasation. In this study we also report that after chemically induced sympathectomy, by chronic pretreatment with 6-hydroxydopamine (6-OHDA), both the plasma extravasation produced by BK and the enhancing effect of PGE 2 are markedly attenuated. Plasma extravasation induced by PGE 2 alone was small and was not significantly attenuated by sympathectomy. We conclude that BK-induced extravasation involves production of at least two sympathetic postganglionic neuron (SPGN) terminal-dependent factors, one of which is a cyclo-oxygenase product of arachidonic acid metabolism, probably PGE 2, (Coderre et al., J. Neurophysiol., 62 (1989) 45–58) and another that is unidentified.

Bradykinin-induced Airway Microvascular Leakage and Bronchoconstriction Are Mediated via a Bradykinin B2Receptor

We have investigated the effects of bradykinin (Bk) antagonists on Bk-induced airway microvascular leakage and bronchoconstriction in mechanically ventilated guinea pigs by simultaneous measuring extravasation of Evans blue dye and airway opening pressure (Pao). Bradykinin (1 microgram/kg intravenously) significantly increased leakage of dye in trachea, main bronchi, and intrapulmonary airways, and increased Pao, indicating airway narrowing. The selective Bk B2 antagonist D-Arg-[Hyp3-Thi5,8-D-Phe7]-Bk (NPC 349; 400 micrograms/kg intravenously) did not alter basal leakage, but when given 2 min before Bk, significantly inhibited the Bk-induced plasma extravasation by 99.8% in the trachea (p less than 0.05), by 75.9% in main bronchi (p less than 0.05), by 83.5% in proximal intrapulmonary airways (p less than 0.05), and by 91.5% in distal intrapulmonary airways (p less than 0.05). NPC 349 also reduced the increase in Pao induced by Bk by 73.5% (p less than 0.05) without affecting the basal Pao. However, NPC 349 had no inhibitory effect on Bk-induced leak or bronchoconstriction when given 30 min before Bk. By contrast, the B1 antagonist des Arg9-Leu8-Bk (500 micrograms/kg intraveneously) had no effect on the Bk-increased plasma extravasation and Pao. We conclude that Bk increases airway plasma leakage and bronchoconstriction via activation of B2 receptors.

Studies on the vascular permeability induced by intrathecal substance P and bradykinin in the rat

The effects of substance P (SP), SP fragments, neurokinin A (NKA), neurokinin (NKB) and selective agonists for neurokinin receptors were assessed on cutaneous vascular permeability after intrathecal (i.t.) administration in rats. Dose-dependent increases in plasma extravasation were observed with the following rank orders of potency ([p-Glu 6] SP-(6–11)>SP⩾SP-(4–11)>[p-Glu 5, MePhe 8, Sar 9]SP-(5–11)=[p-Glu 5]SP-(5–11)>SP-(7–11) an d SP>NKA>NKB). The N-terminal fragments SP-(1–4), SP-(1–7) and SP-(1–9) were inactive. The NK-1 receptor selective agonists ([β-Ala 4, ar 9, Met(O 2) 11]SP-(4–11) and [Pro 9,Met(O 2) 11]SP) were more potent than the NK-2 ([Nle 10]NKA-(4–10)) and NK-3 ([β-Asp 4,MePhe 7]NKB-(4–10) and [MePhe 7]NKB) receptor-selective agonists. Plasma extravasation was also increased by i.t. bradykinin (BK, 8.1 nmol) while the fragment BK-(1–8), a potent B 1-receptor-selective agonist, produced only a slight effect at 81 nmol. When BK was given after prior i.t. administration of 6.1 nmol of [Thi 5,8,D-Phe 7]BK, an antagonist of BK at the B 2-receptor, the increase in vascular permeability was significantly attenuated. The analogue [Leu 8]BK-(1–8) (10.3 nmol), an antagonist of BK at the B 1-receptor, failed to modify the BK-induced plasma extravasation. Plasma extravasation induced by SP (6.5 nmol) and BK (8.1 nmol) was abolished in cervically vagotomized rats, and significantly reduced in both spinal rats and in capsaicin-treated animals. Conversely, bilateral adrenalectomy (48 h earlier) and intercollicular decerebration (30 min earlier) had no major effect on the response elicited either by SP or BK. The response to SP remained unaffected by methysergide and hexamethonium but was significantly reduced by methylnitrate atropine and diphenhydramine. Indomethacin significantly enhanced the plasma extravasation induced by SP. These results suggest that SP and BK may play a role as spinal mediators in peripheral vascular permeability through a sensory and cholinergic vagal mechanism involving a spinobulbar pathway. The receptors mediating the response to SP and BK in the spinal cord are of the NK-1 and B 2 subtypes, respectively.