Intrathecal bradykinin acts presynaptically on spinal noradrenergic terminals to produce antinociception in the rat

Bradykinin induces peripheral antinociception in PGE2-induced hyperalgesia in mice

BACKGROUND

Bradykinin (BK) is an endogenous peptide involved in vascular permeability and inflammation. It has opposite effects (inducing hyperalgesia or antinociception) when administered directly in the central nervous system. The aim of this study was to evaluate whether BK may also present this dual effect when injected peripherally in a PGE₂-induced nociceptive pain model, as well as to investigate the possible mechanisms of action involved in this event in mice.

METHODS

Male Swiss and C57BL/6 knockout mice for B₁ or B₂ bradykinin receptors were submitted to a mechanical paw pressure test and hyperalgesia was induced by intraplantar prostaglandin E₂ (2 µg/paw) injection.

RESULTS

Bradykinin (20, 40 and 80 ng/paw) produced dose-dependent peripheral antinociception against PGE₂-induced hyperalgesia. This effect was antagonized by bradyzide (8, 16 and 32 μg/paw), naloxone (12.5, 25 and 50 μg/paw), nor-binaltorphimine (50, 100 and 200 μg/paw) and AM251 (20, 40 and 80 μg/paw). Bestatin (400 µg/paw), MAFP (0.5 µg/paw) and VDM11 (2.5 µg/paw) potentiated the antinociception of a lower 20 ng BK dose. The knockout of B₁ or B₂ bradykinin receptors partially abolished the antinociceptive action of BK (80 ng/paw), bremazocine (1 μg/paw) and anandamide (40 ng/paw) when compared with wild-type animals, which show complete antinociception with the same dose of each drug.

CONCLUSION

The present study is the first to demonstrate BK-induced antinociception in peripheral tissues against PGE₂-induced nociception in mice and the involvement of κ-opioid and CB₁ cannabinoid receptors in this effect.

Hypersensitivity Induced by Intrathecal Bradykinin Administration Is Enhanced by N-oleoyldopamine (OLDA) and Prevented by TRPV1 Antagonist

Transient receptor potential vanilloid 1 (TRPV1) channels contribute to the development of several chronic pain states and represent a possible therapeutic target in many painful disease treatment. Proinflammatory mediator bradykinin (BK) sensitizes TRPV1, whereas noxious peripheral stimulation increases BK level in the spinal cord. Here, we investigated the involvement of spinal TRPV1 in thermal and mechanical hypersensitivity, evoked by intrathecal (i.t.) administration of BK and an endogenous agonist of TRPV1, N-oleoyldopamine (OLDA), using behavioral tests and i.t. catheter implantation, and administration of BK-induced transient thermal and mechanical hyperalgesia and mechanical allodynia. All these hypersensitive states were enhanced by co-administration of a low dose of OLDA (0.42 µg i.t.), which was ineffective only under the control conditions. Intrathecal pretreatment with TRPV1 selective antagonist SB366791 prevented hypersensitivity induced by i.t. co-administration of BK and OLDA. Our results demonstrate that both thermal and mechanical hypersensitivity evoked by co-administration of BK and OLDA is mediated by the activation of spinal TRPV1 channels.

5-Hydroxytryptamine 1A receptors in the dorsomedial hypothalamus connected to dorsal raphe nucleus inputs modulate defensive behaviours and mediate innate fear-induced antinociception

The dorsal raphe nucleus (DRN) is an important brainstem source of 5-hydroxytryptamine (5-HT), and 5-HT plays a key role in the regulation of panic attacks. The aim of the present study was to determine whether 5-HT1A receptor-containing neurons in the medial hypothalamus (MH) receive neural projections from DRN and to then determine the role of this neural substrate in defensive responses. The neurotracer biotinylated dextran amine (BDA) was iontophoretically microinjected into the DRN, and immunohistochemical approaches were then used to identify 5HT1A receptor-labelled neurons in the MH. Moreover, the effects of pre-treatment of the dorsomedial hypothalamus (DMH) with 8-OH-DPAT and WAY-100635, a 5-HT1A receptor agonist and antagonist, respectively, followed by local microinjections of bicuculline, a GABAA receptor antagonist, were investigated. We found that there are many projections from the DRN to the perifornical lateral hypothalamus (PeFLH) but also to DMH and ventromedial (VMH) nuclei, reaching 5HT1A receptor-labelled perikarya. DMH GABAA receptor blockade elicited defensive responses that were followed by antinociception. DMH treatment with 8-OH-DPAT decreased escape responses, which strongly suggests that the 5-HT1A receptor modulates the defensive responses. However, DMH treatment with WAY-100635 failed to alter bicuculline-induced defensive responses, suggesting that 5-HT exerts a phasic influence on 5-HT1A DMH neurons. The activation of the inhibitory 5-HT1A receptor had no effect on antinociception. However, blockade of the 5-HT1A receptor decreased fear-induced antinociception. The present data suggest that the ascending pathways from the DRN to the DMH modulate panic-like defensive behaviours and mediate antinociceptive phenomenon by recruiting 5-HT1A receptor in the MH.

Spinal dynorphin and bradykinin receptors maintain inflammatory hyperalgesia

An upregulation of the endogenous opioid, dynorphin A, in the spinal cord is seen in multiple experimental models of chronic pain. Recent findings implicate a direct excitatory action of dynorphin A at bradykinin receptors to promote hyperalgesia in nerve injured rats, and its upregulation may promote, rather than counteract, enhanced nociceptive input due to injury. Here we examined a model of inflammatory pain by unilateral injection of complete Freund's adjuvant (CFA) into the rat hind paw. Rats exhibited tactile hypersensitivity and thermal hyperalgesia in the inflamed paw by 6 hours after CFA injection, whereas a significant elevation of prodynorphin transcripts in the lumbar spinal cord was seen at day 3 but not at 6 hours. Thermal hyperalgesia at day 3, but not at 6 hours, after CFA injection was blocked by intrathecal administration of anti-dynorphin antiserum or by bradykinin receptor antagonists. The antihyperalgesic effect of the latter was not due to de novo production of bradykinin or upregulation of spinal bradykinin receptors. These data suggest that elevated spinal dynorphin on peripheral inflammation mediates chronic inflammatory hyperalgesia. The antihyperalgesic effect of bradykinin receptor antagonists requires the presence of upregulated spinal dynorphin but not of de novo production of bradykinin, supporting our hypothesis that pathological levels of dynorphin may activate spinal bradykinin receptors to mediate inflammatory hyperalgesia.

PERSPECTIVE

This study shows that chronic peripheral inflammation induces a significant upregulation of the endogenous opioid peptide dynorphin. Elevated levels of spinal dynorphin and activation of spinal bradykinin receptors are essential to maintain inflammatory hyperalgesia. The results suggest that blockade of spinal bradykinin receptors may have therapeutic potential in chronic inflammatory pain.

Pronociceptive actions of dynorphin via bradykinin receptors

The endogenous opioid peptide dynorphin A is distinct from other endogenous opioid peptides in having significant neuronal excitatory and neurotoxic effects that are not mediated by opioid receptors. Some of these non-opioid actions of dynorphin contribute to the development of abnormal pain resulting from a number of pathological conditions. Identifying the mechanisms and the sites of action of dynorphin is essential for understanding the pathophysiology of dynorphin and for exploring novel therapeutic targets for pain. This review will discuss the mechanisms that have been proposed and the recent finding that spinal dynorphin may be an endogenous ligand of bradykinin receptors under pathological conditions to promote pain.

Involvement of kinin B1 receptor and oxidative stress in sensory abnormalities and arterial hypertension in an experimental rat model of insulin resistance

Diabetes Mellitus leads to pain neuropathy and cardiovascular complications which remain resistant to current therapies involving the control of glycaemia. This study aims at defining the contribution of kinin B(1) receptor (B(1)R) and the oxidative stress on sensory abnormalities and arterial hypertension in a rat model of insulin resistance. Rats were fed with 10% d-glucose for a chronic period of 12-14 weeks and the impact of a diet supplemented with alpha-lipoic acid, a potent antioxidant, was determined on tactile and cold allodynia, arterial hypertension and the expression of kinin B(1)R (real-time PCR and autoradiography) in several tissues. Acute effects of brain penetrant (LF22-0542) and peripherally acting (R-715) B(1)R antagonists were also assessed. Glucose-fed rats exhibited tactile and cold allodynia along with increases in systolic blood pressure between 4 and 12 weeks; these alterations were alleviated by alpha-lipoic acid. The latter regimen also decreased significantly increased plasma levels of insulin and glucose and insulin resistance (HOMA index) at 14 weeks. B(1)R mRNA was virtually absent in liver, aorta, lung, kidney and spinal cord isolated from control rats, yet B(1)R mRNA was markedly increased in all tissues in glucose-fed rats. Up-regulated B(1)R mRNA and B(1)R binding sites (spinal cord) were significantly reduced by alpha-lipoic acid in glucose-fed rats. LF22-0542 reduced tactile and cold allodynia (3h) and reversed arterial hypertension (3-48h) in glucose-fed rats. R-715 abolished tactile and cold allodynia but had not effect on blood pressure. Data suggest that the oxidative stress contributes to the induction and up-regulation of B(1)R in the model of insulin resistance induced by glucose feeding. The over expressed B(1)R contributes centrally to arterial hypertension and in the periphery to sensory abnormalities.

Inhibition of acute nociceptive responses in rats after i.c.v. injection of Thr6-bradykinin, isolated from the venom of the social wasp, Polybia occidentalis

BACKGROUND AND PURPOSE

In this work, a neuroactive peptide from the venom of the neotropical wasp Polybia occidentalis was isolated and its anti-nociceptive effects were characterized in well-established pain induction models.

EXPERIMENTAL APPROACH

Wasp venom was analysed by reverse-phase HPLC and fractions screened for anti-nociceptive activity. The structure of the most active fraction was identified by electron-spray mass spectrometry (ESI-MS/MS) and it was further assessed in two tests of anti-nociceptive activity in rats: the hot plate and tail flick tests.

KEY RESULTS

The most active fraction contained a peptide whose structure was Arg-Pro-Pro-Gly-Phe-Thr-Pro-Phe-Arg-OH, which corresponds to that of Thr(6)-BK, a bradykinin analogue. This peptide was given by i.c.v. injection to rats. In the tail flick test, Thr(6)-BK induced anti-nociceptive effects, approximately twice as potent as either morphine or bradykinin also given i.c.v. The anti-nociceptive activity of Thr(6)-BK peaked at 30 min after injection and persisted for 2 h, longer than bradykinin. The primary mode of action of Thr(6)-BK involved the activation of B(2) bradykinin receptors, as anti-nociceptive effects of Thr(6)-BK were antagonized by a selective B(2) receptor antagonist.

CONCLUSIONS AND IMPLICATIONS

Our data indicate that Thr(6)-BK acts through B(2) bradykinin receptors in the mammalian CNS, evoking antinociceptive behaviour. This activity is remarkably different from that of bradykinin, despite the structural similarities between both peptides. In addition, due to the increased metabolic stability of Thr(6)-BK, relative to that of bradykinin, this peptide could provide a novel tool in the investigation of kinin pathways involved with pain.

Descriptive and functional neuroanatomy of locus coeruleus-noradrenaline-containing neurons involvement in bradykinin-induced antinociception on principal sensory trigeminal nucleus

The present study was carried out in Wistar rats, using the jaw-opening reflex and dental pulp stimulation, to investigate noradrenaline- and serotonin-mediated antinociceptive circuits. The effects of microinjections of bradykinin into the principal sensory trigeminal nucleus (PSTN) before and after neurochemical lesions of the locus coeruleus noradrenergic neurons were studied. Neuroanatomical experiments showed evidence for reciprocal neuronal pathways connecting the locus coeruleus (LC) to trigeminal sensory nuclei and linking monoaminergic nuclei of the pain inhibitory system to spinal trigeminal nucleus (STN). Fast blue (FB) injections in the locus coeruleus/subcoeruleus region retrogradely labeled neurons in the contralateral PSTN and LC. Microinjections of FB into the STN showed neurons labeled in both ipsilateral and contralateral LC, as well as in the ipsilateral Barrington's nucleus and subcoeruleus area. Retrograde tract-tracing with FB also showed that the mesencephalic trigeminal nucleus sends neural pathways towards the ipsilateral PSTN, with outputs from cranial and caudal aspects of the brainstem. In addition, neurons from the lateral and dorsolateral columns of periaqueductal gray matter also send outputs to the ipsilateral PSTN. Microinjections of FB in the interpolar and caudal divisions of the STN labeled neurons in the caudal subdivision of STN. Microinjections in the STN interpolar and caudal divisions also retrogradely labeled serotonin- and noradrenaline-containing nucleus of the brainstem pain inhibitory system. Finally, the gigantocellularis complex (nucleus reticularis gigantocellularis/paragigantocellularis), nucleus raphe magnus and nucleus raphe pallidus also projected to the caudal divisions of the STN. Microinjections of bradykinin in the PSTN caused a statistically significant long-lasting antinociception, antagonized by the damage of locus coeruleus-noradrenergic neuronal fibres with (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine) (DSP4), a neurotoxin that specifically depleted noradrenaline from locus coeruleus terminal fields. These data suggest that serotonin- and noradrenaline-containing nuclei of the endogenous pain inhibitory system exert a key-role in the antinociceptive mechanisms of bradykinin and the locus coeruleus is crucially involved in this effect.

Effects of alpha-lipoic acid on kinin B1 and B2 receptor binding sites in the spinal cord of chronically angiotensin-treated rats

A quantitative autoradiographic study was performed to determine whether kinin receptors are altered in the rat spinal cord in an experimental model of arterial hypertension under antioxidant therapy with alpha-lipoic acid. Sprague-Dawley rats were fed for 4 weeks with a normal chow diet or with an alpha-lipoic acid supplemented diet (1000 mg/kg feed), and treated for the last 2 weeks with angiotensin II (AT II) (200 ng/kg/min with an osmotic pump implanted s.c.). Control rats received either diet but not AT II. A 2-week administration of AT II increased significantly systolic blood pressure, the production of superoxide anion in the aorta and B1 receptor binding sites in the thoracic spinal dorsal horn. This treatment did not affect spinal B2 receptor binding sites, glycemia and insulinemia. The diet supplemented with alpha-lipoic acid reduced significantly the increase in systolic blood pressure, the production of aortic superoxide anion and prevented the increases of B1 receptor binding sites. Results show an association between the oxidative stress and the increases of B1 receptors and arterial blood pressure induced by AT II. Data also exclude the possibility that arterial hypertension is a primary mechanism leading to an increase of B2 receptor binding sites in the rat spinal cord.

Chronic effects of angiotensin-converting enzyme inhibition on kinin receptor binding sites in the rat spinal cord

With the use of in vitro receptor autoradiography, this study aims at determining whether the higher level of kinin B(2) receptor density in the spinal cord of the spontaneously hypertensive rat (SHR) is secondary to arterial hypertension and whether chronic treatment with angiotensin I-converting enzyme inhibitors (ACEI) can regulate neuronal B(1) and B(2) receptors. SHR received, from the age of 4 wk, one of the two ACEI (lisinopril or zofenopril, 10 mg x kg(-1) x day(-1)) or for comparison, the selective AT(1) antagonist (losartan, 20 mg x kg(-1) x day(-1)) in their drinking water for a period of 4, 12, and 20 wk. Age-matched untreated SHR and Wistar-Kyoto rats (WKY) were used as controls. B(2) receptor binding sites in most laminae were higher in SHR than in WKY from the age of 8 to 24 wk. Whereas B(1) receptor binding sites were significantly present in young SHR and WKY, they were barely detectable in adult rats. ACEI (16 and 24 wk) and AT(1) antagonist (24 wk) enhanced the number of B(2) without changing B(1) receptor binding sites. However, at 8 wk the three treatments significantly increased B(1) and decreased B(2) receptors in lamina I. It is concluded that 1) the higher density of B(2) receptors in the spinal cord of SHR is not due to hypertension, 2) kinin receptors are regulated differently by ACEI in neuronal and vascular tissues, and 3) aging may have a profound impact on levels of B(1) and B(2) receptors in the rat spinal cord.

Intrathecal bradykinin administration: opposite effects on nociceptive transmission

Injected intrathecally, bradykinin (BK) produced either hyperalgesia (0.15 microg) or antinociception (6.0 microg) in rats when thermal noxious stimuli were used. Similarly, des-Arg(9)-BK at the lower dose (0.15 microg) decreased, whereas at the higher dose (6.0 microg) it increased the threshold to thermal noxious stimuli; however, these effects were less pronounced than those of BK. The antinociception induced by BK was abolished by HOE 140, a B(2) receptor antagonist, injected intrathecally at a dose of 1.3 ng and was markedly attenuated by des-Arg(10)-HOE 140, a B(1) receptor antagonist (1.15 ng i.t.). The results obtained in this study showed that--depending on the dose used--BK and des-Arg(9)-BK could produce pro- as well as antinociceptive actions. Both B(2) and B(1) receptors are involved in the action of intrathecally applied BK.

Pharmacologic and autoradiographic evidence for an up-regulation of kinin B(2) receptors in the spinal cord of spontaneously hypertensive rats

1. The effects of intrathecally (i.t.) injected kinin B(1) and B(2) receptor agonists and antagonists were measured on mean arterial pressure (MAP) and heart rate (HR) of conscious unrestrained spontaneously hypertensive rats (SHR of 16 weeks old) and age-matched normotensive Wistar Kyoto (WKY). Quantitative in vitro autoradiographic studies were also performed on the thoracic spinal cord of both strains with specific radioligands for B(2) receptors, [(125)I]-HPP-Hoe 140, and B(1) receptors, [(125)I]-HPP-[des-Arg(10)]-Hoe140. 2. Bradykinin (BK) (0.81 - 810 pmol) increased MAP dose-dependently with increases or decreases of HR. The pressor response to BK was significantly greater in SHR. The cardiovascular response to 8.1 pmol BK was reversibly blocked by 81 pmol Hoe 140 (B(2) antagonist) but not by 81 - 810 pmol [des-Arg(10)]-Hoe 140 (B(1) antagonist) in both strains. 3. The B(1) receptor agonist, des-Arg(9)-BK (8100 pmol) produced either no effects or increased MAP with variable effects on HR. These responses were similar in both strains and were reversibly blocked by 81 pmol Hoe 140. Inhibition with 8100 pmol [des-Arg(10)]-Hoe 140 was not specific to B(1) agonist-mediated responses. 4. [(125)I]-HPP-Hoe 140 specific binding sites were predominantly located to superficial laminae of the dorsal horn and were significantly higher in SHR. Low levels of [(125)I]-HPP-[des-Arg(10)]-HOE 140 specific binding sites were found in all laminae of both strains. 5. It is concluded that the hypersensitivity of the cardiovascular response to BK is due to an increased number of B(2) receptors in the spinal cord of SHR and that B(1) receptors are unlikely involved in spinal cardiovascular regulation in SHR.

Kinin receptors in pain and inflammation

Kinins are among the most potent autacoids involved in inflammatory, vascular and pain processes. These short-lived peptides, including bradykinin, kallidin and T-kinin, are generated during tissue injury and noxious stimulation. However, emerging evidence also suggests that kinins are stored in neuronal elements of the central nervous system (CNS) where they are thought to play a role as neuromediators in various cerebral functions, particularly in the control of nociceptive information. Kinins exert their biological effects through the activation of two transmembrane G-protein-coupled receptors, denoted bradykinin B(1) and B(2). Whereas the B(2) receptor is constitutive and activated by the parent molecules, the B(1) receptor is generally underexpressed in normal tissues and is activated by kinins deprived of the C-terminal Arg (des-Arg(9)-kinins). The induction and increased expression of B(1) receptor occur following tissue injury or after treatment with bacterial endotoxins or cytokines such as interleukin-1 beta and tumor necrosis factor-alpha. This review summarizes the most recent data from various animal models which convey support for a role of B(2) receptors in the acute phase of the inflammatory and pain response, and for a role of B(1) receptors in the chronic phase of the response. The B(1) receptor may exert a strategic role in inflammatory diseases with an immune component (diabetes, asthma, rheumatoid arthritis and multiple sclerosis). New information is provided regarding the role of sensory mechanisms subserving spinal hyperalgesia and intrapleural neutrophil migration that occur upon B(1) receptor activation in streptozotocin-treated rats, a model of insulin-dependent diabetes mellitus in which the B(1) receptor seems to be rapidly overexpressed. Although it is widely accepted that the blockade of kinin receptors with specific antagonists could be of benefit in the treatment of somatic and visceral inflammation and pain, recent molecular and functional evidence suggests that the activation of B(1) receptors with an agonist may afford a novel therapeutic approach in the CNS inflammatory demyelinating disorder encountered in multiple sclerosis by reducing immune cell infiltration (T-lymphocytes) into the brain. Hence, the B(1) receptor may exert either a protective or detrimental effect depending on the inflammatory disease. This dual function of the B(1) receptor deserves to be investigated further.

Pharmacological characterization of the cardiovascular responses elicited by kinin B(1) and B(2) receptor agonists in the spinal cord of streptozotocin-diabetic rats

Kinin receptor agonists and antagonists at the B(1) and B(2) receptors were injected intrathecally (i.t., at T-9 spinal cord level) to conscious unrestrained rats and their effects on mean arterial pressure (MAP) and heart rate (HR) were compared in streptozotocin (STZ)-diabetic rats (65 mg kg(-1) STZ, i.p. 3 weeks earlier) and aged-matched control rats. The B(1) receptor agonist, des-Arg(9)-Bradykinin (BK) (3.2 - 32.5 nmol), evoked dose-dependent increases in MAP and tachycardia during the first 10 min post-injection in STZ-diabetic rats only. The cardiovascular response to 6.5 nmol des-Arg(9)-BK was reversibly blocked by the prior i.t. injection of antagonists for the B(1) receptor ([des-Arg(10)]-Hoe 140, 650 pmol or [Leu(8)]-des-Arg(9)-BK, 65 nmol) and B(2) receptor (Hoe 140, 81 pmol or FR173657, 81 pmol) or by indomethacin (5 mg kg(-1), i.a.). The i.t. injection of BK (8.1 - 810 pmol) induced dose-dependent increases in MAP which were accompanied either by tachycardiac (STZ-diabetic rats) or bradycardiac (control rats) responses. The pressor response to BK was significantly greater in STZ-diabetic rats. The cardiovascular response to 81 pmol BK was reversibly blocked by 81 pmol Hoe 140 or 81 pmol FR173657 but not by B(1) receptor antagonists nor by indomethacin in STZ-diabetic rats. The data suggest that the activation of kinin B(1) receptor in the spinal cord of STZ-diabetic rats leads to cardiovascular changes through a prostaglandin mediated mechanism. Thus, this study affords an accessible model for studying the expression, the pharmacology and physiopathology of the B(1) receptor in the central nervous system.

Effect of diabetes on bradykinin-induced thermal hyperalgesia in mice

To investigate the role of protein kinase C in the attenuation of bradykinin-induced thermal hyperalgesia in diabetic mice, we examined the effects of a protein kinase C activator or inhibitor on the i.t. bradykinin-induced hyperalgesia in diabetic and non-diabetic mice. Intrathecal injection of bradykinin caused a transient antinociceptive effect, which diminished within 30 min, and then produced a thermal hyperalgesia, which lasted about 120 min, in non-diabetic mice. Although the duration of the antinociceptive phase was longer in diabetic mice than in non-diabetic mice, the hyperalgesic response was not observed in diabetic mice. The bradykinin-induced hyperalgesia was dose-dependently and significantly enhanced by pretreatment with calphostin C (0.3 to 3 pmol, i.t.), a specific protein kinase C inhibitor, in diabetic mice. However, calphostin C (3 pmol, i.t.) had no significant effect on bradykinin-induced hyperalgesia in non-diabetic mice. On the other hand, pretreatment with phorbol-12, 13-dibutyrate (12.5 to 50 pmol, i.t.), a protein kinase C activator, significantly and dose-dependently reduced bradykinin-induced hyperalgesia in non-diabetic mice. However, phorbol-12, 13-dibutyrate (50 pmol, i.t. ) had no significant effect on bradykinin-induced hyperalgesia in diabetic mice. These results suggest that the change in bradykinin-induced thermal hyperalgesia in diabetic mice may be due, at least in part, to the modification of nociceptive transmission in the spinal cord by the activation of protein kinase C.

Pharmacology and cardiovascular implications of the kinin-kallikrein system

Kinins are peptide hormones that can exert a significant influence on the regulation of blood pressure and vascular tone due to their vasodilatatory, natriuretic and growth modulating activity. Their cardiovascular involvement in physiological and pathophysiological situations has been studied intensively since inhibitors for angiotensin I-converting enzyme and selective receptor antagonists have become available for pharmacologically potentiating or inhibiting kinin-mediated reactions. Molecular biological analysis and the establishment of genetically modified animal models have also allowed newer information to be acquired on this subject. In this review, the components and cardiovascularly relevant mechanisms of the kinin-kallikrein system shall be described. Organ-specific effects concerning the kidneys, the vascular system, the heart and nervous tissue shall also be illustrated. On this issue, the physiological functions and pathophysiological implications of the kinin-kallikrein system should be clearly distinguished from the many, mostly endothelium-mediated protective effects which occur during ACE inhibition due to the potentiation of kinin effects. Finally, a view shall also be cast upon newly discovered targets of action, which could be exploited for therapeutically altering the kinin-kallikrein system.

Brain sites involved in the antinociceptive effect of bradykinin in rats

The localization of brain sites where bradykinin (BK) induces its antinociceptive effect in rats, was studied using as index the threshold for the jaw-opening reflex elicited by the dental pulp electrical stimulation test (DPEST). The microinjection of BK into the lateral or fourth cerebral ventricles induced an antinociceptive effect, with Index of Antinociception (IA) of 0.51+/-0.03 and 0.68+/-0.05, respectively. However, microinjections of the peptide into the third ventricle induced a less marked antinociception (IA = 0.28+/-0.08). The brain sites where the microinjection of BK caused an antinociceptive effect were: locus coeruleus, principal nucleus, oral part of the spinal sensorial trigeminal nucleus, and the sensory root of the trigeminal nerve. The antinociceptive effect was more intense when BK (4-16 nmol) was injected into the locus coeruleus. Microinjection of BK (4 nmol) into the fourth ventricle, but not into the locus coeruleus, induced an increase in blood pressure. The microinjection of the peptide into the nucleus tractus solitarius, a site that is also involved in the pressor effect of BK, did not induce an antinociceptive effect. These results indicate that the antinociceptive effect of BK is not related to blood pressure changes. The microinjection of BK into some of the sites involved in the mechanisms of analgaesia, including the periaqueductal gray matter (dorsal, lateral and ventrolateral) and the dorsal raphe nucleus did not induce an antinociceptive effect. The results suggest that the most likely brain sites involved in the antinociceptive effect of BK are the locus coeruleus and the principal sensory trigeminal nucleus. The present results did not exclude the involvement of other brain sites surrounding the lateral and the third ventricles.

Pathophysiology of the kallikrein-kinin system in mammalian nervous tissue

The nervous system and peripheral tissues in mammals contain a large number of biologically active peptides and proteases that function as neurotransmitters or neuromodulators in the nervous system, as hormones or cellular mediators in peripheral tissue, and play a role in human neurological diseases. The existence and possible functional relevance of bradykinin and kallidin (the peptides), kallikreins (the proteolytic enzymes), and kininases (the peptidases) in neurophysiology and neuropathological states are discussed in this review. Tissue kallikrein, the major cellular kinin-generating enzyme, has been localised in various areas of the mammalian brain. Functionally, it may assist also in the normal turnover of brain proteins and the processing of peptide-hormones, neurotransmitters, and some of the nerve growth factors that are essential for normal neuronal function and synaptic transmission. A specific class of kininases, peptidases responsible for the rapid degradation of kinins, is considered to be identical to enkephalinase A. Additionally, kinins are known to mediate inflammation, a cardinal feature of which is pain, and the clearest evidence for a primary neuronal role exists so far in the activation by kinins of peripherally located nociceptive receptors on C-fibre terminals that transmit and modulate pain perception. Kinins are also important in vascular homeostasis, the release of excitatory amino acid neurotransmitters, and the modulation of cerebral cellular immunity. The two kinin receptors, B2 and B1, that modulate the cellular actions of kinins have been demonstrated in animal neural tissue, neural cells in culture, and various areas of the human brain. Their localisation in glial tissue and neural centres, important in the regulation of cardiovascular homeostasis and nociception, suggests that the kinin system may play a functional role in the nervous system.

Pressor effect mediated by bradykinin in the paratrigeminal nucleus of the rat

1. The participation of the paratrigeminal nucleus (Pa5) in the pressor response produced by bradykinin in the dorsolateral medulla of rats was investigated. The microinjection of 6 pmol of bradykinin directly over the paratrigeminal nucleus of unanaesthetized rats produced a significant increase in arterial pressure and a moderate increase in heart rate. 2. Bradykinin microinjections in different sites surrounding the Pa5 compromising the external cuneate nucleus, the trigeminal nucleus, the lateral and ventral spinal trigeminal tract and the dorsal trigeminal tract rostral and caudal to the Pa5 did not elicit significant pressor responses. In contrast, microinjections in the paratrigeminal nucleus produced pressor effects. Injections in the dorsolateral medulla directly over the paratrigeminal nucleus produced larger responses than when injections were made in the nucleus. Saline injections in the different nuclei did not produce pressor effects. 3. Neurochemical lesioning of the Pa5, with microinjections of ibotenic acid in the Pa5, abolished the pressor response to bradykinin injected over the lesioned nucleus. The effect was present, however, when bradykinin was injected on the contralateral side to the lesion, over the intact nucleus of the same animal. Pretreatment with capsaicin (injected in the lateral cerebral ventricle), which causes selective degeneration of afferent sensory fibres, did not alter the pressor effect of bradykinin injected over the paratrigeminal nucleus. 4. Dose-related responses were produced by different concentrations of bradykinin (0.6-1.8 pmol) microinjected over the nucleus. The bradykinin receptor antagonist HOE 140, injected over the paratrigeminal nucleus 30 min earlier, abolished the pressor response caused by bradykinin. 5. Low doses of bradykinin injected in or directly over the paratrigeminal nucleus increased arterial pressure and caused a small increase in heart rate by stimulating kinin receptors of the paratrigeminal nucleus in the dorsolateral medulla of awake and unrestrained rats. The pattern of the response was consistent with that of sympathetic stimulation. The paratrigeminal nucleus, which receives primary afferents and projects to the nucleus tractus solitarii and the rostral ventral lateral medulla, may be positioned as relay nucleus possibly connecting sensory input to structures that regulate blood pressure.

Distribution of bradykinin B2 receptors in sheep brain and spinal cord visualized by in vitro autoradiography

Bradykinin B2 receptors were localized in the sheep brain and spinal cord by quantitative in vitro autoradiography using a radiolabelled and specific bradykinin B2 receptor antagonist analogue, 3-4-hydroxyphenyl-propionyl-D-Arg0-[Hyp3,Thi5,D-Tic 7,Oic8]bradykinin, (HPP-HOE 140). This radioligand displays high affinity and specificity for bradykinin B2 receptors. The respective K(i) values of 0.32, 1.37 and 156 nM were obtained for bradykinin, HOE140 and D-Arg[Hyp3,D-Phe7,Leu8]bradykinin competing for radioligand binding to lamina II of sheep spinal cord sections. Using this radioligand, we have demonstrated the distribution of bradykinin B2 receptors in many brain regions which have not been previously reported. The highest density of bradykinin B2 receptors occur in the pleoglial periaqueductal gray, oculomotor and trochlear nuclei and the circumventricular organs. Moderate densities of receptors occur in the substantia nigra, particularly the reticular part, the posterior thalamic and subthalamic nuclei, zona incerta, the red and pontine nuclei, some of the pretectal nuclei and in discrete layers of the superior colliculus. In the hindbrain, moderate levels of bradykinin B2 receptor binding occur in the nucleus of the solitary tract, and in spinal trigeminal, inferior olivary, cuneate and vestibular nuclei. Laminae II, X and dorsal root ganglia display the most striking binding densities in the spinal cord, while the remainder of the dorsal and ventral horn display a low and diffuse density of binding. Bradykinin B2 receptors are extensively distributed throughout the sheep brain and spinal cord, not only to sensory areas but also to areas involved in motor activity.

Central involvement of kinin B1 and B2 receptors in the febrile response induced by endotoxin in rats

1. The effect of central injection of selective kinin B1 and B2 receptor antagonists on the febrile response induced by endotoxin (E. coli lipopolysaccharide, LPS) in rats was investigated. 2. Intracerebroventricular (i.c.v.) injection of a selective B2 receptor antagonist (Hoe-140, 8 nmol) reduced the early (0-2 h), but increased the late phase (4-6 h) of the febrile response induced by intravenous (i.v.) injection of LPS (0.5 microgram kg-1). 3. Co-administration of Hoe-140 (8 nmol, i.c.v.) with LPS (0.5 microgram kg-1, i.v.), followed 2.5 h later by the i.c.v. injection of a selective B1 receptor antagonist [des-Arg9-Leu8]-bradykinin (BK, 8 nmol), significantly reduced the febrile response induced by LPS throughout the whole experimental period. 4. Intravenous injection of Hoe-140 (1 mg kg-1) significantly reduced the febrile response induced by LPS (0.5 microgram kg-1, i.p.). 5. Pretreatment (24 h) with LPS (0.5 microgram kg-1, i.v.) reduced the febrile response induced by BK or [Tyr8]-BK (both, 5 nmol, i.c.v.), but markedly increased the febrile response induced by [des-Arg9]-BK (5 nmol, i.c.v.). The response induced by [des-Arg9]-BK in LPS-pretreated rats was significantly inhibited by co-injection of [des-Arg9-Leu8]-BK (15 nmol, i.c.v.). 6. The results suggest that kinins are involved in the induction of LPS-induced fever and that central B2 and B1 receptors are activated during the initial and late phase of this response, respectively. The results also suggest that downregulation and/or desensitization of B2 receptors and induction and/or upregulation of B1 receptors in LPS-pretreated animals may have a significant pathophysiological role in the induction and maintenance of fever. These observations may be specifically important in the case of chronic inflammatory conditions, because the BK metabolite [des-Arg9]-BK, so far considered an inactive metabolite, acquires an active and relevant role with the progressive expression of B1 receptors that occurs in such states.

Localization of bradykinin-like immunoreactivity in the rat spinal cord: effects of capsaicin, melittin, dorsal rhizotomy and peripheral axotomy

A putative role for bradykinin has been proposed in the processing of sensory information at the level of the spinal cord. Autoradiographic studies have demonstrated the presence of B2 kinin receptor binding sites in superficial laminae of the dorsal horn and a down-regulation of those receptors in rat models of pain injury. In this study, classical immunocytochemistry and confocal microscopy immunofluorescence were used first to localize bradykinin-like immunoreactivity in all major spinal cord segments of naive rats; second, to assess bradykinin-like immunoreactivity changes that occur in animals subjected to various chemical treatments and surgical lesions. High densities of bradykinin-like immunoreactivity were observed in motoneuron of the ventral horn, deeper laminae and nucleus dorsalis of the dorsal horn. Higher magnification of ventral horn showed strong immunostaining of motoneuron perikaryas and their proximal processes. Two types of bradykinin-like immunoreactivity immunostained cellular bodies were observed in deeper laminae of the dorsal horn. These interneurons, morphologically corresponding to islets and antenna-type cells project dendrites to adjacent laminae. Furthermore, numerous strongly marked dendrites, transversally cut, suggest the presence of projection neurons to higher cervical centres. Following unilateral lumbar dorsal rhizotomy (L1-L6) or peripheral lesion of the sciatic nerve, important increases of bradykinin-like immunoreactivity were found in laminae III and IV of the ipsilateral dorsal horn. In contrast, significant decreases of immunodeposits were observed in both cell bodies and numerous dendrites of motoneuron surrounding neuropil. Specific destructions of sensory afferent fibres with capsaicin or selective activation of kallikreins with melittin caused increases of bradykinin-like immunoreactivity in both the dorsal and ventral horns of the spinal cord. These results which demonstrate the cellular localization of bradykinin-like immunoreactivity in both dorsal and ventral horns of the rat spinal cord, further reveal the plasticity of this non-sensory peptidergic system following various chemical and surgical treatments. Hence, these anatomical findings along with earlier functional and receptor autoradiographic studies reinforce the putative role of bradykinin in sensory function.

Possible role of nitric oxide in the antinociceptive action of intraventricular bradykinin in mice

The i.c.v. administration of bradykinin (4, 8 and 16 micrograms) induced antinociception in mice which was resistant to naloxone; furthermore, the induction of tolerance to morphine by a single s.c. injection (100 mg/kg, 24 h before test doses of the peptide) did not affect antinociception. Since bradykinin is known to increase nitric oxide (NO) in peripheral tissues, we studied the possibility that its antinociceptive action may be related to NO effects in the central nervous system. Bradykinin effects were antagonized by previous treatment with NG-nitro-L-arginine or concomitant i.c.v. administration of bradykinin and methylene blue. The immediate precursor of NO, L-arginine, which by itself produces analgesia, also reduced bradykinin effects; moreover, tolerance to L-arginine significantly decreased the response to the peptide. These results suggest that NO is involved in antinociception induced by i.c.v. administration of bradykinin.

Central B2 receptor involvement in the antinociceptive effect of bradykinin in rats

1. The effect of intracerebroventricular (i.c.v.) injection of bradykinin (BK) and related peptides was tested on the dental pulp electrical stimulation threshold (DPEST) in rats. 2. BK (4, 8 and 16 nmol) induced a dose-dependent increase of DPEST, indicative of an antinociceptive effect. 3. I.c.v. injection of equimolar doses of BK-related peptides, Lys-BK and Met-Lys-BK, also induced an increase of DPEST, but the magnitude of the effect was not as intensive as that induced by BK, when the maximum increase of DPEST was considered. The peptide T-kinin induced a short lasting and weak antinociceptive effect. 4. The B1 agonist, des-Arg9-BK (8 nmol) induced a significant antinociceptive effect, but this was not as intensive as that induced by BK. 5. The B2 antagonist D-Arg0-Hyp3-Thi5,8-D-Phe7-BK (D-Arg0) competitively antagonized the BK-induced antinociception. Likewise, Hyp3-Thi5,8-D-Phe7-BK (Hyp) also antagonized BK effect. However, the compound Thi5,8-D-Phe7-BK (Thi), initially considered a pure BK antagonist, induced an antinociceptive effect, supporting previous observations that this peptide can also act as a partial agonist. 6. It is concluded that the dose-dependent antinociceptive effect induced by i.c.v. injection of BK is mediated by the stimulation of brain B2 receptors.

Quantitative autoradiographic localization of [125I-Tyr8]bradykinin receptor binding sites in the rat spinal cord: effects of neonatal capsaicin, noradrenergic deafferentation, dorsal rhizotomy and peripheral axotomy

In vitro receptor autoradiography was used to localize, quantify and characterize [125I-Tyr8]bradykinin binding sites in all major spinal cord segments of normal rats and animals subjected to various chemical treatments and surgical lesions. [125I-Tyr8]bradykinin specific binding sites were predominantly located to superficial laminae of the rat dorsal horn, with the substantia gelatinosa showing the highest density of labelling (values ranging from 3.1 fmol/mg tissue in cervical to 4.5 fmol/mg tissue in lumbar segments). A moderate density (1.8-3.0 fmol/mg tissue) of specific binding was observed in lamina III, whereas in other areas, i.e. laminae I and IV-X, lower amounts of labelling were detected. Within the superficial laminae of the dorsal horn, [125I-Tyr8]bradykinin binding was largely distributed over the neurophil with some perikarya showing concentrations of labelling. In contrast, the ventral horn showed a rather homogeneous distribution of [125I-Tyr8]bradykinin binding over the neuropil, with silver grain alignments surrounding motoneuron perikaryas and proximal processes. Bradykinin, [Tyr8]bradykinin and B2 receptor antagonists (D-Arg[Hyp3,Thi5,D-Tic7,Oic8]bradykinin (Hoe 140), D-Arg[Tyr3,D-Phe7,Leu8]bradykinin, D-Arg[Hyp3, Leu8]bradykinin, D-Arg[Hyp2, Thi5,8,-Phe7]bradykinin D-Arg[Hyp3, D-Phe7, Leu8]bradykinin, Tyr0, D-Arg[Hyp3, D-Phe7, Leu8]bradykinin inhibited [125I-Tyr8]-bradykinin binding with very high subnanomolar affinities, while the B1 receptor agonist (Tyr0,des-Arg10-kallidin) and antagonist ([Leu8]-des-Arg9-bradykinin) did not significantly affect [125I-Tyr8]bradykinin binding at up to micromolar concentrations. Two weeks after unilateral lumbar dorsal rhizotomy (L1-L6) or peripheral lesions of the sciatic nerve, significant decreases ( +/- 50%) in [125I-Tyr8]bradykinin binding sites were found in ipsilateral laminae I-III of lumbar spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)

Bradykinin modulation of alpha 2-adrenoceptors in the nucleus tractus solitarii of the rat. An in vitro autoradiographical study

The existence of an interaction between bradykinin (Bk) receptors and the alpha 2-adrenoceptors were evaluated by means of quantitative receptor autoradiography in the nucleus tractus solitarii (NTS) of the rat. In competition experiments using L-noradrenaline (0.1 nM to 10 microM) against [3H]p-aminoclonidine ([3H]PAC) (10 nM) it was observed that Bk produced an increase in the IC50 value of L-noradrenaline in a concentration response manner, which reached a maximum of about 100% with 10 nM of the peptide associated with a small decrease in the B0 value (15%). In saturation experiments Bk promoted a significant increase in the KD value of [3H]PAC (60%) and a decrease in the Bmax value (36%). The specific Bk B2 receptor antagonist HOE-140 fully counteracted the effect of Bk on the alpha 2-adrenoceptors as analyzed by the competition experiments. Furthermore, des-Arg9-Bk, a Bk analog which exhibits selective agonist activity to the Bk B1 receptor subtype did not produce any effect on the alpha 2-adrenoceptors, suggesting that the Bk B2 receptor subtype may be mediating the Bk action on the alpha 2-adrenoceptors in the NTS. The effect of Bk (10 nM) was analyzed together with GTP (0.1 nM) in competition experiments and no change in the ability of L-noradrenaline to compete for [3H]PAC binding sites was observed in the presence of GTP, suggesting that the receptor interaction between the Bk B2 receptors and the alpha 2-adrenoceptors may be a G-protein dependent mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinins and kinin receptors in the nervous system

Kinins, including bradykinin and kallidin, are peptides that are produced and act at the site of tissue injury or inflammation. They induce a variety of effects via the activation of specific B1 or B2 receptors that are coupled to a number of biochemical transduction mechanisms. In the periphery the actions of kinins include vasodilatation, increased vascular permeability and the stimulation of immune cells and peptide-containing sensory neurones to induce pain and a number of neuropeptide-induced reflexes. Mechanisms for kinin synthesis are also present in the CNS where kinins are likely to initiate a similar cascade of events, including an increase in blood flow and plasma leakage. Kinins are potent stimulators of neural and neuroglial tissues to induce the synthesis and release of other pro-inflammatory mediators such as prostanoids and cytotoxins (cytokines, free radicals, nitric oxide). These events lead to neural tissue damage as well as long lasting disturbances in blood-brain barrier function. Animal models for CNS trauma and ischaemia show that increases in kinin activity can be reversed either by kinin receptor antagonists or by the inhibition of kinin production. A number of other central actions have been attributed to kinins including an effect on pain signalling, both within the brain (which may be related to vascular headache) and within the spinal dorsal horn where primary afferent nociceptors can be stimulated. Kinins also appear to play a role in cardiovascular regulation especially during chronic spontaneous hypertension. Presently, however, direct evidence is lacking for the release of kinins in pathophysiological conditions of the CNS and it is not known whether spinal or central neurones, other than afferent nerve terminals, are sensitive to kinins. A more detailed examination of the effects of kinins and their central pharmacology is necessary. It is also important to determine whether the inhibition of kinin activity will alleviate CNS inflammation and whether kinin receptor antagonists are useful in pathological conditions of the CNS.

Bradykinin excites tetrodotoxin-resistant primary afferent fibers

Bradykinin is a nonapeptide that plays a central role in the production of pain and inflammation. A horizontal spinal cord slice preparation with attached dorsal root and dorsal root ganglion was used to study the effect of bradykinin on afferent fibers. Intracellular recordings were made from dorsal root ganglion and dorsal horn neurons. Bath application of bradykinin (1 microM) to the dorsal root ganglion compartment produced a depolarization (5 +/+ 0.8 mV) and firing of action potentials in eight out of eighteen dorsal root ganglion neurons tested. Simultaneous intracellular recordings from dorsal horn neurons revealed that the application of bradykinin to dorsal root ganglion, peripheral nerve trunk or dorsal root resulted in the synaptic activation of dorsal horn neurons. The depolarizing effect of bradykinin on the dorsal root ganglion neurons and its synaptic excitatory effect on dorsal horn neurons was abolished by pretreatment of the same segment of sensory neurons by a B2 bradykinin receptor antagonist (D-Arg0,Hyp3,beta-Thi5,8,D-Phe7)-bradykinin (5 microM). Bath application of tetrodotoxin (TTX; 0.2-1 microM) to the sensory neurons blocked electrically-evoked action potentials in large dorsal root ganglion neurons and, consequently, excitatory postsynaptic potentials in dorsal horn neurons evoked by electrical activation of low threshold afferent fibers. However, the stimulatory effects, both depolarization and firing of action potentials, of bradykinin were resistant to TTX. Replacement of sodium ions with TRIS completely abolished the stimulatory effect of bradykinin on the sensory neurons. Bradykinin potentiated the postsynaptic potentials induced by electrical stimulation of TTX-resistant afferent fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoradiographic localization of [125I-Tyr8]-bradykinin receptor binding sites in the guinea pig spinal cord

The present study aimed to localize and characterize [125I-Tyr8]-BK binding sites in all major segments of the guinea pig spinal cord using in vitro quantitative receptor autoradiography. [125I-Tyr8]-BK specific binding sites were localized predominantly in superficial layers of the dorsal horn, with lamina II depicting the highest labelling. The density of specific binding in laminae I and III was moderate, whereas in other areas, i.e., laminae IV-X, lower amounts of labelling were noticed. The B2 receptor antagonists D-Arg[Hyp3,Thi5,D-Tic7,Oic8]-BK (Hoe 140), D-Arg[Hyp3,D-Phe7,Leu8]-BK, Tyr0,D-Arg[Hyp3,D-Phe7,Leu8]-BK, D-Arg[Tyr3,D-Phe7,Leu8]-BK, D-Arg[Hyp2,Thi5,8,D-Phe7]-BK, D-Arg[Hyp3,Leu8]-BK and D-Arg[Hyp3,Gly6,Leu8]-BK as well as unlabelled [Tyr8]-BK inhibited [125I-Tyr8]-BK binding with respective Ki values of 0.04, 12.4, 23.4, 34.5, 43.5, 33.5, 23.0, and 0.6 nM while B1 related molecules (Tyr0,des-Arg10-kallidin and [Leu8]-des-Arg9-BK) did not significantly inhibit [125I-Tyr8]-BK binding up to micromolar concentrations. These results indicate that the specific [125I-Tyr8]-BK binding sites present in the guinea pig spinal cord belong to the B2 receptor subtype. The high density of B2 binding sites in the substantia gelatinosa provides an anatomical evidence in favour of a role for BK as a modulator of nociceptive information.

Effect of bradykinin and prostaglandins on the release of calcitonin gene-related peptide-like immunoreactivity from the rat spinal cord in vitro

1. The release of calcitonin gene-related peptide-like immunoreactivity (CGRP-LI) from the dorsal horn of the rat spinal cord in vitro in response to dorsal root stimulation was measured by radioimmunoassay. 2. Stimulation of the dorsal roots (3 or 4 roots on each side) at 10 Hz for 5 min evoked a mean release (R1) of 134.3 +/- 17.5 (n = 10) fmol CGRP-LI; the release (R2) evoked by a second stimulation period 30 min later under control conditions was 77 +/- 10% (n = 10) of R1. Test compounds were applied to the preparation following release R1, and their effect calculated from the value of R2/R1. 3. Bradykinin (0.01-10 microM) had no significant effect on the basal release of CGRP-LI, but at 0.1-10 microM it increased 2-3 fold the release evoked by dorsal root stimulation. 4. This effect of bradykinin was prevented by indomethacin (10 microM), or by the B2-receptor antagonist, Hoe140 (1-10 microM). In the presence of Hoe140, bradykinin significantly reduced R2/R1; the explanation for this is not clear. 5. The B1-receptor agonist, Des-Arg9-bradykinin (10 microM), did not affect CGRP-LI release nor was the effect of bradykinin blocked by the B1-receptor antagonist, Des-Arg9-Leu8-bradykinin (10 microM). 6. Various prostaglandins were found to mimic the effect of bradykinin on CGRP-LI release. Their approximate order of potency was prostaglandin D2 (PGD2) = PGE1 > PGF2 alpha = PGE2; PGI2 was ineffective at 10 microM.7. Forskolin (30 muM) and 3-isobutyl l-methylxanthine (IBMX; 10 fM) also increased the evoked release of CGRP-LI.8. It is concluded that bradykinin acts on B2-receptors in the spinal cord, causing the formation ofprostanoids, which in turn cause an enhancement of neuropeptide release from primary afferent nerve terminals in the dorsal horn. This effect may be secondary to activation of adenylate cyclase. Because B2-receptors are mainly associated with primary afferent nerve terminals, it is likely that prostanoid production is also a function of these structures. Whether this action of bradykinin has any physiological function in nociceptive transmission remains unclear..

Opioid mediation of the antiaversive and hyperalgesic actions of bradykinin injected into the dorsal periaqueductal gray of the rat

Reported evidence indicates that the dorsal region of the periaqueductal gray matter (PAG) is involved in the modulation of both pain and aversion, and that opioid mechanisms, among others, participate in their modulation. Since many central actions of bradykinin (BK) have been shown to be similar to those of morphine, the present was undertaken to measure the effects of microinjection of BK into the PAG on the thresholds of aversive electrical stimulation of the same brain area and of dental pulp electrical stimulation. Bradykinin, injected into the dorsal PAG, induced a dose-dependent increase in the aversive threshold, an effect similar to that reported by others for morphine. Also, as reported for morphine, the antiaversive effect of BK was antagonized by naloxone injected intraperitoneally. Whereas subcutaneously administered morphine induced marked analgesia, intra-PAG administration of BK caused a small but significant hyperalgesia. Similarly, morphine injected into the dorsal PAG tended to cause hyperalgesia instead of analgesia. Furthermore, the hyperalgesic effect of BK also appears to involve opioid mechanisms since it was blocked by naloxone. As in previously reported studies, intracerebroventricularly injected BK raised the pain threshold. These results indicate that BK mobilizes opioid mechanisms in the dorsal PAG that inhibit aversion but not pain.

Cardiovascular responses elicited by intrathecal kinins in the conscious rat

In the conscious, unrestrained rat, intrathecal (i.t.) injection of 0.81 pmol-81 nmol bradykinin (BK), kallidin (KD) and T-kinin at the T-9 spinal cord level produced transient (less than 10 min) increases in mean arterial pressure (MAP) and longer lasting decreases in heart rate (HR). These effects were dose-dependent and similar with respect to intensity and time course for the three kinins. The des-Arg9-BK fragment, a selective agonist for B1 receptors, was active only at 81 nmol. The pressor response induced by BK was enhanced by propranolol and by transection of the cervical spinal cord but was converted to a vasodepressor effect by prazosin. The bradycardia was converted to tachycardia by prazosin, atropine, pentolinium, capsaicin and in spinal transected rats. However, the cardiovascular responses to BK remained unaffected by diphenhydramine plus cimetidine, morphine, indomethacin, adrenal medullectomy, i.t. idazoxan and after bulbospinal noradrenaline deafferentation with 6-hydroxydopamine. These results suggest that the increase in MAP induced by i.t. BK is mediated by the sympathoadrenal system while the decrease in HR is ascribable to a vagal reflex involving sensory C-fibers and a spinobulbar pathway. This pharmacological evidence therefore supports a role for kinins in cardiovascular regulation in the spinal cord.

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 B (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-Glu6]SP-(6-11) greater than SP greater than or equal to SP-(4-11) greater than [p-Glu5,MePhe8,Sar9]SP-(5-11) = [p-Glu5]SP-(5-11) greater than SP-(7-11) and SP greater than NKA greater than NKB). The N-terminal fragments SP-(1-4), SP-(1-7) and SP-(1-9) were inactive up to 65 nmol. The NK-1 receptor selective agonists [( beta-Ala4,Sar9,Met(O2)11]SP-(4-11) and [Pro9,Met(O2)11]SP) were more potent than the NK-2 ([Nle10]NKA-(4-10] and NK-3 ([beta-Asp4,MePhe7]NKB-(4-10) and [MePhe7]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 B1-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 [Thi5.8,D-Phe7]BK, an antagonist of BK at the B2-receptor, the increase in vascular permeability was significantly attenuated. The analogue [Leu8]BK-(1-8) (10.3 nmol), an antagonist of BK at the B1-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 B2 subtypes, respectively.

Bradykinin-induced depolarization of primary afferent nerve terminals in the neonatal rat spinal cord in vitro

1. Application of bradykinin (BK) to the spinal cord of the neonatal rat evoked depolarizations which could be recorded via either the dorsal or ventral roots. However, responses recorded via the ventral root were abolished by removal of extracellular Ca2+ or the addition of Cd2+, while responses recorded via the dorsal root were unaffected. 2. The response recorded via the ventral root was inhibited by the substance P antagonist spantide, while responses recorded via the dorsal root were unaffected. 3. Depolarizations recorded via the dorsal root were concentration-dependent with an EC50 of 30 nM. These responses were not antagonized by the BK1 selective antagonist Leu8des-Arg9BK, but were antagonized by D-Arg0Hyp3Thi5,8D-Phe7BK with a pA2 of 6.8 +/- 0.6, which is similar to the values determined for other BK2-mediated responses. 4. Application of phorbol dibutyrate (PDBu) to the spinal cord also evoked a depolarization with respect to the dorsal root. This response to PDBu was enhanced by removal of extracellular Ca2+, while the response to BK was unaffected. 5. The potent protein kinase inhibitor staurosporine reduced the response to PDBu, but did not affect the response to BK. 6. These results suggest that BK by acting on BK2 receptors can depolarize the central terminals of primary afferent nerve fibres. This response to BK does not appear to be mediated via the activation of protein kinase C. The depolarization to BK recorded via the ventral root of the spinal cord is indirect and may be secondary to the action of BK on the primary afferent terminals.