Effect of des arginine9-bradykinin and other bradykinin fragments on the synthesis of prostacyclin and the binding of bradykinin by vascular cells in culture

The Role of the Kinin System and the Effect of Des-Arginine9-Bradykinin on Coagulation and Platelet Function in Critically Ill COVID-19 Patients: A Secondary Analysis of a Prospective Observational Study

The effect of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on the coagulation system is not fully understood. SARS-CoV-2 penetrates cells through angiotensin-converting enzyme 2 (ACE2) receptors, leading to its downregulation. Des-arginine9-bradykinin (DA9B) is degraded by ACE2 and causes vasodilation and increased vascular permeability. Furthermore, DA9B is associated with impaired platelet function. Therefore, the aim of this study was to evaluate the effects of DA9B on platelet function and coagulopathy in critically ill coronavirus disease 2019 (COVID-19) patients. In total, 29 polymerase-positive SARS-CoV-2 patients admitted to the intensive care unit of the University Hospital of Giessen and 29 healthy controls were included. Blood samples were taken, and platelet impedance aggregometry and rotational thromboelastometry were performed. Enzyme-linked immunosorbent assays measured the concentrations of DA9B, bradykinin, and angiotensin 2. Significantly increased concentrations of DA9B and angiotensin 2 were found in the COVID-19 patients. A negative effect of DA9B on platelet function and intrinsic coagulation was also found. A sub-analysis of moderate and severe acute respiratory distress syndrome patients revealed a negative association between DA9B and platelet counts and fibrinogen levels. DA9B provokes inhibitory effects on the intrinsic coagulation system in COVID-19 patients. This negative feedback seems reasonable as bradykinin, which is transformed to DA9B, is released after contact activation. Nevertheless, further studies are needed to confirm our findings.

Sensory and signaling mechanisms of bradykinin, eicosanoids, platelet-activating factor, and nitric oxide in peripheral nociceptors

Peripheral mediators can contribute to the development and maintenance of inflammatory and neuropathic pain and its concomitants (hyperalgesia and allodynia) via two mechanisms. Activation or excitation by these substances of nociceptive nerve endings or fibers implicates generation of action potentials which then travel to the central nervous system and may induce pain sensation. Sensitization of nociceptors refers to their increased responsiveness to either thermal, mechanical, or chemical stimuli that may be translated to corresponding hyperalgesias. This review aims to give an account of the excitatory and sensitizing actions of inflammatory mediators including bradykinin, prostaglandins, thromboxanes, leukotrienes, platelet-activating factor, and nitric oxide on nociceptive primary afferent neurons. Manifestations, receptor molecules, and intracellular signaling mechanisms of the effects of these mediators are discussed in detail. With regard to signaling, most data reported have been obtained from transfected nonneuronal cells and somata of cultured sensory neurons as these structures are more accessible to direct study of sensory and signal transduction. The peripheral processes of sensory neurons, where painful stimuli actually affect the nociceptors in vivo, show marked differences with respect to biophysics, ultrastructure, and equipment with receptors and ion channels compared with cellular models. Therefore, an effort was made to highlight signaling mechanisms for which supporting data from molecular, cellular, and behavioral models are consistent with findings that reflect properties of peripheral nociceptive nerve endings. Identified molecular elements of these signaling pathways may serve as validated targets for development of novel types of analgesic drugs.

The enhanced permeability retention effect: a new paradigm for drug targeting in infection

Multidrug-resistant, Gram-negative infection is a major global determinant of morbidity, mortality and cost of care. The advent of nanomedicine has enabled tailored engineering of macromolecular constructs, permitting increasingly selective targeting, alteration of volume of distribution and activity/toxicity. Macromolecules tend to passively and preferentially accumulate at sites of enhanced vascular permeability and are then retained. This enhanced permeability and retention (EPR) effect, whilst recognized as a major breakthrough in anti-tumoral targeting, has not yet been fully exploited in infection. Shared pathophysiological pathways in both cancer and infection are evident and a number of novel nanomedicines have shown promise in selective, passive, size-mediated targeting to infection. This review describes the similarities and parallels in pathophysiological pathways at molecular, cellular and circulatory levels between inflammation/infection and cancer therapy, where use of this principle has been established.

Mechanisms in bradykinin stimulated arachidonate release and synthesis of prostaglandin and platelet activating factor

Regulatory mechanisms in bradykinin (BK) activated release of arachidonate (ARA) and synthesis of prostaglandin (PG) and platelet activating factor (PAF) were studied in bovine pulmonary artery endothelial cells (BPAEC). A role for GTP binding protein (G-protein) in the binding of BK to the cells was determined. Guanosine 5-O- (thiotriphosphate), (GTPtauS), lowered the binding affinity for BK and increased the Kd for the binding from 0.45 to 1.99 nM. The Bmax remained unaltered at 2.25 x 10(-11) mole. Exposure of the cells to aluminium fluoride also reduced the affinity for BK. Bradykinin-induced release of ARA proved pertussis toxin (PTX) sensitive, with a maximum sensitivity at 10 ug/ml PTX. GTPtauS at 100 muM increased the release of arachidonate. The effect of GTPtauS and BK was additive at suboptimal doses of BK up to 0.5 nM but never exceeded the levels of maximal BK stimulation at 50 nM. PTX also inhibited the release of ARA induced by the calcium ionophore, A23187. Phorbol 12-myristate 13-acetate or more commonly known as tetradecanoyl phorbol acetate (TPA) itself had little effect on release by the intact cells. However, at 100 nM it augmented the BK activated release. This was downregulated by overnight exposure to TPA and correlated with down-regulation of protein kinase C (PKC) activity. The down-regulation only affected the augmentation of ARA release by TPA but not the original BK activated release. TPA displayed a similar, but more potent amplification of PAF synthesis in response to both BK or the calcium ionophore A23187. These results taken together point to the participation of G-protein in the binding of BK to BPAEC and its activation of ARA release. Possibly two types of G-protein are involved, one associated with the receptor, the other activated by Ca(2+) and perhaps associated with phospholipase A(2) (PLA(2)). Our results further suggest that a separate route of activation, probably also PLA(2) related, takes place through a PKC catalysed phosphorylation.

Vascular permeability enhancement in solid tumor: various factors, mechanisms involved and its implications

Most solid tumors are known to exhibit highly enhanced vascular permeability, similar to or more than the inflammatory tissues. Common denominators affecting both cancer and inflammatory lesions are now well known: bradykinin (BK), nitric oxide (NO), peroxynitrite (ONOO(-)), prostaglandins (PGs), collagenases or matrix metalloproteinases (MMPs) and others. Incidentally, enzymes involved in these mediator syntheses are upregulated or activated. Initially described vascular permeability factor (VPF) (proteinaceous) was later identified to be the same as vascular endothelial growth factor (VEGF), which promotes angiogenesis of cancer tissues as well. These mediators cross-talk or co-upregulate each other, such as BK-NO-PGs system. Therefore, vascular permeability observed in solid tumor may reflect the other side of the coin (angiogenesis). The vascular permeability and accumulation of plasma components in the interstitium described here is applicable for predominantly macromolecules (molecular weight, Mw>45 kDa), but not for low molecular compounds as most anticancer agents are. Macromolecular compounds (e.g., albumin, transferrin) or many biocompatible water-soluble polymers show this effect. Furthermore, they are not cleared rapidly from the sites of lesion (cancer/inflammatory tissue), thus, remain for prolonged time, usually for more than a few days. This phenomenon of "enhanced permeability and retention effect" observed in cancer tissue for macromolecules and lipids is coined "EPR effect", which is now widely accepted as a gold standard for anticancer drug designing to seek more cancer-selective targeting using macromolecular drugs. Consequently, drastic reduction of the systemic side effect is observed, while the macromolecular drugs will continuously exert antitumor activity. Other advantages of macromolecular drugs are also discussed.

Modulation of tumor-selective vascular blood flow and extravasation by the stable prostaglandin 12 analogue beraprost sodium

Improved delivery of macromolecular drugs to solid tumor is known as the enhanced permeability and retention (EPR) effect of macromolecular drugs and lipids. We report here that a prostaglandin I2 (PGI2) analogue induces enhancement of tumor-selective drug delivery, while it decreases tumor blood flow, in a rat tumor model (AH136B). Beraprost sodium (BPS) is an analogue of PGI2 that is more stable than parental PGI2 in vivo (t1/2 for BPS is > 1 h vs. a few seconds for PGI2). Thus, BPS was administered to tumor-bearing rats to examine its effect on tumor vascular permeability as well as tumor blood flow. The amount of extravasation of the Evans blue-albumin complex in tumor tissue increased from two to three times, whereas tumor blood flow decreased almost 70%, in the group treated with BPS at 7 (microg/kg compared with controls. Tissue blood flow of normal organs such as the kidney and the liver did not change to a significant extent. These findings establish a new role for BPS, not only in enhancing macromolecular drug delivery, but also in reducing the blood supply to tumor tissues.

Mechanisms regulating the expression, self-maintenance, and signaling-function of the bradykinin B2 and B1 receptors

Bradykinin (BK) is a potent short-lived effector belonging to a class of peptides known as kinins. It participates in inflammatory and vascular regulation and processes including angioedema, tissue permeability, vascular dilation, and smooth muscle contraction. BK exerts its biological effects through the activation of the bradykinin B2 receptor (BKB2R) which is G-protein-coupled and is generally constitutively expressed. Upon binding, the receptor is activated and transduces signal cascades which have become paradigms for the actions of the Galphai and Galphaq G-protein subunits. Following activation the receptor is then desensitized, endocytosed, and resensitized. The bradykinin B1 (BKB1R) is a closely related receptor. It is activated by desArg(10)-kallidin or desArg(9)-BK, metabolites of kallidin and BK, respectively. This receptor is induced following tissue injury or after treatment with bacterial endotoxins such as lipopolysacharide or cytokines such as interleukin-1 or tumor necrosis factor-alpha. In this review we will summarize the BKB2R and BKB1R mediated signal transduction pathways. We will then emphasize the relevance of key residues and domains of the intracellular regions of the BKB2R as they relate to modulating its function (signal transduction) and self-maintenance (desensitization, endocytosis, and resensitization). We will examine the features of the BKB1R gene promoter and its mRNA as these operate in the expression and self-maintenance of this inducible receptor. This communication will not cover areas discussed in earlier reviews pertaining to the actions of peptide analogs. For these we refer you to earlier reviews (Regoli and Barabé, 1980, Pharmacol Rev 32:1-46; Regoli et al., 1990, J Cardiovasc Pharmacol 15(Suppl 6):S30-S38; Regoli et al., 1993, Can J Physiol Pharmacol 71:556-557; Marceau, 1995, Immunopharmacology 30:1-26; Regoli et al., 1998, Eur J Pharmacol 348:1-10).

Des-Arg(10)-kallidin engagement of the B1 receptor stimulates type I collagen synthesis via stabilization of connective tissue growth factor mRNA

Expression of the kinin B1 receptor is up-regulated in chronic inflammatory and fibrotic disorders; however, little is known about its role in fibrogenesis. We examined human embryonic lung fibroblasts that constitutively express the B1 receptor and report that engagement of the B1 receptor by des-Arg(10)-kallidin stabilized connective tissue growth factor (CTGF) mRNA, stimulated an increase in alpha1(I) collagen mRNA, and stimulated type I collagen production. These events were not observed in B2 receptor-activated fibroblasts. In addition, B1 receptor activation by des-Arg(10)-kallidin induced a rise in cytosolic Ca(2+) that is consistent with B1 receptor pharmacology. Our results show that the des-Arg(10)-kallidin-stimulated increase in alpha1(I) collagen mRNA was time- and dose-dependent, with a peak response observed at 20 h with 100 nM des-Arg(10)-kallidin. The increase in CTGF mRNA was also time- and dose-dependent, with a peak response observed at 4 h with 100 nM des-Arg(10)-kallidin. The increase in CTGF mRNA was blocked by the B1 receptor antagonist des-Arg(10),Leu(9)-kallidin. Inhibition of protein synthesis by cycloheximide did not block the des-Arg(10)-kallidin-induced increase in CTGF mRNA. These results suggest that engagement of the kinin B1 receptor contributes to fibrogenesis through increased expression of CTGF.

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.

Mechanisms in the transcriptional regulation of bradykinin B1 receptor gene expression. Identification of a minimum cell-type specific enhancer

To investigate the mechanisms of bradykinin B1 (BKB1) receptor gene expression, transient DNA transfection analyses of human BKB1 receptor gene promoter were performed in SV-40 transformed IMR90 cells. A positive regulatory element (PRE) located at position -604 to -448 base pair (bp) upstream of the transcription start site consistently exhibited, by far, the highest level of relative luciferase activity. A negative regulatory element, at position -682 to -604 bp, was able to completely ablate the function of the PRE. Transfection combined with deletion and mutation analyses illustrated that the PRE contains a classic, powerful enhancer. This enhancer was minimized to a 100-bp element at position -548 to -448 bp. A 78-bp fragment of negative regulatory element functioned as a silencer. Transient transfection of the enhancer construct, driven by heterologous herpes simplex thymidine kinase promoter, into a variety of cell types, showed that this enhancer presents a cell-type specific feature. In the characterization of the enhancer, motifs A (-548 to -532) and B (-483 to -477) were found to be essential for full enhancer activity. Motif D (-472 to -467) played a smaller role in enhancer activation. Gel shift and antibody supershift assays determined that an AP-1 factor binds with motif B. The nuclear protein which binds to motif A has yet to be identified. Both factors are the critical regulators for this enhancer activation.

Characterization of the receptor and the mechanisms underlying the inflammatory response induced by des-Arg9-BK in mouse pleurisy

1 The characterization of the B1 kinin receptor, and some mediators involved in the inflammatory response elicited by intrathoracic (i.t.) administration of des-Arg9-bradykinin (BK) in the mouse model of pleurisy, was investigated. 2 An i.t. injection of des-Arg9-BK (10-100 nmol per site), a selective B1 agonist, caused a significant and dose-related increase in the vascular permeability observed after 5 min, which peaked at 1 h, associated with an increase in cell influx, mainly neutrophils, and, to a lesser extent, mononuclear cell influx, peaking at 4 h and lasting for up to 48 h. The increase in fluid leakage caused by des-Arg9-BK was completely resolved 4 h after peptide injection. I.t. injection of Lys-des-Arg9-BK (30 nmol per site) caused a similar inflammatory response. 3 Both the exudation and the neutrophil influx elicited by i.t. injection of des-Arg9-BK were significantly antagonized (P<0.01) by an i.t. injection of the selective B1 antagonists des-Arg9-[Leu8]-BK (60 and 100 nmol per site) or des-Arg9-NPC 17731 (5 nmol per site), administered in association with des-Arg9-BK (P<0.01), or 30 and 60 min before the cellular peak, respectively. In contrast, an i.t. injection of the B2 bradykinin selective receptor antagonist Hoe 140 (30 nmol per site), at a dose which consistently antagonized bradykinin (10 nmol per site)-induced pleurisy, had no significant effect on des-Arg9-BK-induced pleurisy. 4 An i.t. injection of the selective tachykinin receptor antagonists (NK1) FK 888 (1 nmol per site), (NK2) SR 48968 (20 nmol per site) or (NK3) SR 142801 (10 nmol per site), administered 5 min before pleurisy induction, significantly antagonized neutrophil migration caused by i.t. injection of des-Arg9-BK. In addition, FK 888 and SR 142801, but not SR 48968, also prevented the influx of mononuclear cells in response to i.t. injection of des-Arg9-BK (P<0.01). However, the NK3 receptor antagonist SR 142801 (10 nmol per site) also significantly inhibited des-Arg9-BK-induced plasma extravasation. An i.t. injection of the calcitonin gene-related peptide (CGRP) receptor antagonist CGRP8-37 (1 nmol per site), administered 5 min before pleurisy induction, inhibited des-Arg9-BK-induced plasma extravasation (P<0.01), without significantly affecting the total and differential cell migration. 5 The nitric oxide synthase inhibitors L-NOARG and L-NAME (1 pmol per site), administered 30 min beforehand, almost completely prevented des-Arg9-BK (i.t.)-induced neutrophil cell migration (P<0.01), and, to a lesser extent, mononuclear cell migration (P<0.01). The D-enantiomer D-NAME had no effect on des-Arg9-BK-induced pleurisy. At the same dose range, L-NOARG and L-NAME inhibited the total cell migration (P<0.01). L-NAME, but not L-NOARG caused significant inhibition of des-Arg9-BK-induced fluid leakage. Indomethacin (1 mg kg(-1), i.p.), administered 1 h before des-Arg9-BK (30 nmol per site), inhibited the mononuclear cell migration (P<0.05), but, surprisingly, increased the neutrophil migration at 4 h without interfering with plasma extravasation. The administration of terfenadine (50 mg kg(-1), i.p.), 30 min before des-Arg9-BK (30 nmol per site), did not interfere significantly with the total cell migration or with the plasma extravasation in the mouse pleurisy caused by i.t. injection of des-Arg9-BK. 6 Pretreatment of animals with the lipopolysaccharide of E. coli (LPS; 10 microg per animal, i.v.) for 24 h did not result in any significant change of the inflammatory response induced by i.t. injection of des-Arg9-BK compared with the saline treated group. However, the identical treatment of mice with LPS resulted in a marked enhancement of des-Arg9-BK induced paw oedema (P<0.01). 7 In conclusion, we have demonstrated that the inflammatory response induced by i.t. injection of desArg9-BK, in a murine model of pleurisy, is mediated by stimulation of constitutive B1 receptors. (These responses are largely mediated by release of neuropeptides such as substanceP or CGRP and also by NO, but products derived from cyclo-oxygenase pathway and histamine seem not to be involved. Therefore, these results further support the notion that the B1 kinin receptor has an important role in modulating inflammatory responses, and it is suggested that selective B1 antagonists may provide therapeutic benefit in the treatment of inflammatory and allergic conditions.

Enhanced bradykinin-stimulated phospholipase C activity in murine embryonic stem cells lacking the G-protein alphaq-subunit

The gene coding for the G-protein alphaq subunit was interrupted by homologous recombination in murine embryonic stem cells (alphaq-null ES cells) as detected by Southern analysis and reverse-transcriptase PCR. The bradykinin (BK) B2 receptor was stably transfected into wild-type (WT) alphai-2-null and alphaq-null ES cells. The B2 receptor bound BK with high affinity and mobilized Ca2+. BK also activated phospholipase C (PLC), as determined by total inositol phosphate (IP) accumulation in a Bordetella pertussis toxin- and genistein-insensitive manner. In WT and alphai-2-null ES cells, BK increased IP levels approx. 4-fold above baseline. Most interestingly, in alphaq-null ES cells, BK increased IP accumulation approx. 9-fold above baseline. Re-expression of alphaq in alphaq-null ES cells resulted in normalization of the BK-stimulated IP accumulation (4-fold above baseline). These results suggest that the B2 receptor activates PLC through more than one member of the Gq family. Additionally, the absence of alphaq alters the kinetics of IP generation, which may reflect intrinsic characteristics of individual members of the Gq family or a decreased susceptibility to heterologous regulation in the alphaq-null ES cells, thus allowing for a more sustained generation of IP.

Ischemia and reperfusion in pancreas

Ischemic diseases of heart and brain are the primary causes of mortality in industrialized nations. The ischemic injury with the consecutive reperfusion is responsible for the disturbance of microcirculation with ensuing tissue damage and organ dysfunction. Recent evidence suggests that oxygen-derived free radicals and activated polymorphonuclear leukocytes produced in ischemic tissue are instrumental in the development of ischemic cell injury. In pancreas, ischemia/ reperfusion is proposed as a potentially damaging factor accounting in part for the pathogenesis of acute pancreatitis. Apart from ischemia/reperfusion injury, the kallikrein-kinin system mediates acute inflammation associated with enhanced capillary permeability and accumulation of polymorphonuclear leukocytes, cardinal features of ischemia/reperfusion injury also in acute pancreatitis. Therefore, it seems reasonable to use bradykinin-antagonists to influence postischemic reperfusion injury of the pancreas. In the following, we describe the pathophysiology of ischemia/reperfusion injury with special reference to the pancreatic microcirculation and morphological changes as observed in a model of complete and reversible ischemia. Furthermore, we will discuss the effects of two bradykinin-antagonists (HOE 140 and CP-0597) on functional integrity of the pancreas after ischemia/ reperfusion.

B1 bradykinin receptors and sensory neurones

1. The location of the B1 bradykinin receptors involved in inflammatory hyperalgesia was investigated. 2. No specific binding of the B1 bradykinin receptor ligand [3H]-des-Arg10-kallidin was detected in primary cultures of rat dorsal root ganglion neurones, even after treatment with interleukin-1 beta (100 iu ml-1). 3. In dorsal root ganglion neurones, activation of B2 bradykinin receptors stimulated polyphosphoinositidase C. In contrast, B1 bradykinin receptor agonists (des-Arg9-bradykinin up to 10 microM and des-Arg10-kallidin up to 1 microM) failed to activate polyphosphoinositidase C, even in neurones that had been treated with interleukin-1 beta (100 iu ml-1), prostaglandin E2 (1 microM) or prostaglandin I2 (1 microM). 4. Dorsal root ganglion neurones removed from rats (both neonatal and 14 days old) that had been pretreated with inflammatory mediators (Freund's complete adjuvant, or carrageenan) failed to respond to B1 bradykinin receptor selective agonists (des-Arg9-bradykinin up to 10 microM and des-Arg10-kallidin up to 1 microM). 5. Bradykinin (25 nM to 300 nM) evoked ventral root responses when applied to peripheral receptive fields or central terminals of primary afferents in the neonatal rat spinal cord and tail preparation. In contrast, des-Arg9-bradykinin (50 nM to 500 nM) failed to evoke ventral root depolarizations in either control rats or in animals that developed inflammation following ultraviolet irradiation of the tail skin. 6. The results of the present study imply that the B1 bradykinin receptors that contribute to hypersensitivity in models of persistent inflammatory hyperalgesia are located on cells other than sensory neurones where they may be responsible for releasing mediators that sensitize or activate the nociceptors.

The bradykinin antagonist CP-0597 can limit the progression of postischemic pancreatitis

Bradykinin mediates the inflammatory process of acute pancreatitis characterized by an increase of microvascular permeability, vasodilation and leukocyte activation. These phenomena are characteristic also for the ischemia/reperfusion injury of the pancreas, which in time is considered a causative factor in the pathogenesis of acute pancreatitis. The aim of this study was to investigate the influence of the bradykinin B2 receptor antagonist CP-0597. After complete ischemia/reperfusion of the pancreas in rats there is progression from postischemic acute edema to necrotizing pancreatitis over a reperfusion period of 5 days. In 8 Sprague-Dawley rats (treatment group) 18 micrograms/kg/h CP-0597 was administered intraperitoneally over 5 days with an osmotic minipump starting 15 min before release of 2 h ischemia. Animals of the placebo group (n = 8) were identically treated, but received the solvent, phosphate buffer. Animals of a control group (n = 7) underwent sham operation without ischemia. After 5 days the animals were sacrificed for histology. No morphological changes of the pancreatic gland were observed in the control group. Ischemia for 2 h resulted in necrotizing pancreatitis with high mortality (4/8 animals) during the reperfusion period of 5 days. In contrast, all animals in the treatment group survived without clinical or histological signs of necrotizing pancreatitis.

Bradykinin enhances GLUT4 translocation through the increase of insulin receptor tyrosine kinase in primary adipocytes: evidence that bradykinin stimulates the insulin signalling pathway

It has been suggested that bradykinin stimulates glucose uptake in experiments in vivo and in cultured cells. However, its mechanism has not yet been fully elucidated. In this study, the effects of bradykinin on the insulin signalling pathway were evaluated in isolated dog adipocytes. The bradykinin receptor binding study revealed that dog adipocytes possessed significant numbers of bradykinin receptors (Kd = 83 pmol/l, binding sites = 1.7 x 10(4) site/ cell). Reverse transcription-polymerase chain reaction amplification showed the mRNA specific for bradykinin B2 receptor in the adipocytes. Bradykinin alone did not increase 2-deoxyglucose uptake in adipocytes; however, in the presence of insulin (10(-7) mol/l) it significantly increased 2-deoxyglucose uptake in a dose-dependent manner. Bradykinin also enhanced insulin stimulated GLUT4 translocation from the intracellular fraction to the cell membrane, and insulin induced phosphorylation of the insulin receptor beta subunit and insulin receptor substrate-1 (IRS-1) without affecting the binding affinities or numbers of cell surface insulin receptors in dog adipocytes. The time-course of insulin stimulated phosphorylation of the insulin receptor beta subunit revealed that phosphorylation reached significantly higher levels at 10 min, and stayed at the higher levels until 120 min in the presence of bradykinin, suggesting that bradykinin delayed the dephosphorylation of the insulin receptor. It is concluded that bradykinin could potentiate insulin induced glucose uptake through GLUT4 translocation. This effect could be explained by the potency of bradykinin to upregulate the insulin receptor tyrosine kinase activity which stimulates phosphorylation of IRS-1, followed by GLUT4 translocation.

Sympathetic-dependence in bradykinin-induced synovial plasma extravasation is dose-related

While previous studies have implicated a role for sympathetic postganglionic neuron-terminals in bradykinin-induced plasma extravasation, a recent report by Cambridge and Brain [Br. J. Pharmacol., 115 (1995) 641-647] has suggested that it is sympathetic-independent. However, the doses of bradykinin used in these two groups of studies were considerably different. Therefore, in the present study, we characterized the sympathetic-dependence of plasma extravasation at varying doses of bradykinin. By measuring the concentration of Evans blue dye extravasation into the joint perfusate following its intravenous injection, bradykinin-induced plasma extravasation in the knee joint cavity was determined spectrophotometrically. To examine the role of sympathetic postganglionic neuron terminals in mediating bradykinin-induced plasma extravasation, we used surgical ablation of the lumbar sympathetic chain. Intra-articular perfusion of BK dose-dependently increased synovial plasma extravasation. After surgical sympathectomy, the dose-response curve for bradykinin-induced plasma extravasation was significantly shifted to the right. We conclude that at concentrations observed in inflamed tissues (between 10(-8) and 10(-7) M), bradykinin-induced plasma extravasation is largely mediated by sympathetic postganglionic neuron terminals.

Upregulation of B1 receptor mediating des-Arg9-BK-induced rat paw oedema by systemic treatment with bacterial endotoxin

1. The effect of pretreatment with bacterial endotoxin (LPS, 10 micrograms, i.v., 24 h) on the bradykinin B1 and B2 receptor-induced oedema in the rat paw, and the interaction of B1-mediated responses with other inflammatory mediators, was investigated. 2. Intraplantar (i.pl.) injection of the selective B1 agonist, des-Arg9-BK (DABK, 100 nmol) in naive animals pretreated with the angiotensin converting enzyme inhibitor, captopril caused a small increase in paw volume (0.04 +/- 0.003 ml, mean +/- s.e. mean, n = 6), while the B2-selective agonist, tyrosine8-bradykinin (T-BK, 3 nmol) induced marked oedema (0.36 +/- 0.02 ml). However, i.pl. injection of DABK (3-300 nmol) in rats pretreated with LPS (24 h beforehand) resulted in a marked dose- and time-related increase in paw volume, with mean ED50 of 24.1 nmol. In contrast, oedema caused by T-BK (3 nmol) was reduced by 79 +/- 4% in animals treated with LPS when compared with naive animals. 3. Oedema caused by prostaglandin E2 (PGE2, 10 nmol) was unaffected by LPS treatment, while oedema induced by histamine (100 nmol), 5-hydroxytryptamine (5-HT, 10 nmol) and substance P (SP, 3 nmol) was reduced (P < 0.05). 4. The selective B1 antagonist, des-Arg9[Leu8]-BK (100-300 nmol), produced dose-dependent inhibition of DABK (100 nmol)-induced paw oedema in LPS-treated animals with mean IC50 of 134 nmol, while the selective B2 antagonists, Hoe 140 and NPC 17731 (each 10 nmol), had no effect. 5. Treatment of animals with dexamethasone (0.5 mg kg-1, s.c.) 24 or 48 h prior to LPS injection resulted in a graded inhibition of DABK (100 nmol)-induced oedema formation (58 +/- 3 and 82 +/- 2%, respectively), and almost reversed to control value oedema formation induced by T-BK (3 nmol) in LPS-pretreated rats. Cycloheximide (1 mg kg-1, s.c.) or indomethacin (2 mg kg-1, i.p.) pretreatment 24 and 1 h prior to LPS injection, respectively, markedly inhibited DABK (100 nmol)-induced paw oedema (98 +/- 2 and 50 +/- 4%, respectively). 6. Intraplantar injection of submaximal dose of DABK (10 nmol) in LPS-treated rats produced modest paw oedema (0.09 +/- 0.03 ml). However, i.pl. injections of PGE2, prostacyclin (PGI2), calcitonin-gene-related peptide (CGRP), SP, 5-HT, or platelet activating factor (PAF) (each 1 nmol), which alone caused little or no paw oedema, resulted in a potentiation of the DABK-induced oedema. The increases in paw volume (in ml) were: PGE2 + DABK (0.31 +/- 0.03), PGI2 + DABK (0.39 +/- 0.02), CGRP+DABK (0.35 +/- 0.04), DABK+SP (0.33 +/- 0.04), DABK + 5-HT (0.40 +/- 0.02) and DABK+PAF (0.38 +/- 0.016) ml. In contrast, histamine (1 nmol) was ineffective in potentiating the response to DABK. 7. The selective B1 receptor antagonist, DALBK (100-300 nmol), produced dose-dependent inhibition of paw oedema potentiation induced by co-injection of DABK and other mediators with mean ID50S (nmol) of: 180, 160, 139 and 135 in the presence of PGE2, PGI2, SP and 5-HT, respectively. 8. These results demonstrate that DABK-induced increase in paw volume in LPS-treated rats is probably mediated by induction of B1 receptors, associated with downregulation of B2 receptors. The induction of B1 receptors by LPS is sensitive to dexamethasone and cycloheximide treatment and requires activation of cyclo-oxygenase pathway. In addition, B1 receptors, when upregulated following LPS treatment, can interact in a synergistic manner with several inflammatory mediators such as PGI2, PGE2, CGRP, PAF and 5-HT. Such results indicate that induction of the B1 receptor might have a significant pathophysiological role in modulating chronic inflammatory diseases.

Kinin B1 receptors: a review

The kinin B1 receptor has been initially defined as the one mediating the contractile effect of bradykinin (BK)-related peptides in the isolated rabbit aorta. The B1 receptor is selectively sensitive to kinin metabolites without the C-terminal arginine residue, e.g. des-Arg9-BK and Lys-des-Arg9-BK; it is apparently rapidly up-regulated in immunopathology under the influence of cytokines and is further regulated by growth factors. Progress in the understanding of this pharmacologic entity is reviewed, including the development of B1 receptor agonists and antagonists, binding assays, physiopathological applications and the recent cloning and sequencing of the receptor cDNA.

The involvement of bradykinin B1 and B2 receptor mechanisms in cytokine-induced mechanical hyperalgesia in the rat

1. Interleukin-1 beta (IL-1 beta), IL-2 and IL-8 induced a mechanical hyperalgesia following intra-articular (i.artic.) injection into rat knee joints, whereas IL-6 and tumour necrosis factor alpha (TNF-alpha) were without effect. 2. Co-administration of IL-1 receptor antagonist (0.1 micrograms) with IL-1 beta (1 mu), IL-2 (10 mu) or IL-8 (0.1 mu) prevented the subsequent development of the hyperalgesia. 3. Co-administration of desArg9Leu8BK (0.5-5 nmol) with IL-1 beta (1 mu), IL-2 (10 mu) or IL-8 (0.1 mu) reduced the level of hyperalgesia at 1, 4 and 6 h post administration, whereas Hoe 140 (5 pmol) antagonized the hyperalgesia only at the 1 h time point. 4. Intravenous administration of desArg9Leu8BK (10 nmol kg-1) or Hoe 140 (100 pmol kg-1) following IL-1 beta (1 mu), IL-2 (10 mu), or IL-8 (0.1 mu) reversed the subsequent hyperalgesia. 5. Administration of desArg9BK into joints 24 h after pre-treatment with IL-1 beta (1 mu) produced analegsia at low doses (50 pmol) and hyperalgesia at a higher dose (0.5 nmol). Both these effects were blocked by desArg9Leu8BK (0.5 nmol). 6. Administration of desArg9BK (0.5 nmol i.artic.) to animals 24 h after pre-treatment with IL-2 (1-100 mu) or IL-8 (0.1-10 mu) had no effect on the load tolerated by the treated joint. 7. Administration of indomethacin (1 mg kg-1, s.c.) prior to IL-1 beta (1 mu i.artic.) prevented the development of hyperalgesia. Administration of desArg9BK (5 pmol-0.5 nmol, i.artic.) to animals 24 h after indomethacin and IL-1 beta pretreatment had no effect on the load tolerated by the treated joint. 7. Administration of indomethacin (1 mg kg-1, s.c.) prior to IL-1beta (1 u i.artic.) prevented the development of hyperalgesia. Administration of desArg9BK (5 pmol-0.5 nmol, i.artic.) to animals 24 h after indomethacin and IL-1 beta pretreatment had no effect on the load tolerated by the treated joint.8. These data suggest that both bradykinin B1 and B2 receptors are involved in the induction and maintenance of cytokine-induced hyperalgesia. They also show that the induction of B1 receptor-mediated hyperalgesia requires both cyclo-oxygenase products and IL-1 in vivo.

Interleukin-1 beta induced-desArg9bradykinin-mediated thermal hyperalgesia in the rat

The induction of desArg9Bk-mediated thermal hyperalgesia has been studied in the rat. Intraplantar injections of interleukin-1 beta, (IL-1 beta, 1-100 Units, U) produced a 30-40% decrease in withdrawal latency to noxious heat which lasted for up to 24 hr in the treated paw. IL-1 beta-induced thermal hyperalgesia was also present in the contralateral paw for up to 1 hr following IL-1 beta injection. Intraplantar tumour necrosis factor-alpha (TNF alpha, 500 U) also reduced the withdrawal latency in the u.v.-treated paw with recovery by 18 hr but with no contralateral hyperalgesia. Forty-eight hr after IL-1 beta but not after TNF alpha administration, desArg9Bk (10 nmol/kg i.v.) reduced the withdrawal latency in both the ipsi- and contra-lateral paws by 30-49%. In naive animals, desArg9Bk was without effect. These data suggest that, in the rat, IL-1 beta but not TNF alpha can lead to the induction of bradykinin B1 receptors mediating thermal hyperalgesia.

Induction of B1 receptors in vivo in a model of persistent inflammatory mechanical hyperalgesia in the rat

The induction of mechanical hyperalgesia by B1 and B2 receptor agonists following an inflammatory insult has been studied in the rat. Intra-articular injection of bradykinin, but not desArg9 bradykinin, into naïve joints induced mechanical hyperalgesia with a reduction of up to 38% in load tolerated by the treated leg. Following intra-articular injection of Freund's complete adjuvant (FCA) the load tolerated by the treated leg was depressed for three days. The development of FCA-induced hyperalgesia was reduced by desArg9Leu8BK or Hoe 140. Bradykinin, desArg9BK and the metabolically stable B1 receptor agonist SarDPhe8desArg9BK were all hyperalgesic upon intra-articular administration 3 days after FCA administration. The hyperalgesia induced by desArg9BK and SarDPhe8desArg9BK was prevented by co-administration of desArg9Leu8BK but not by Hoe 140. At low doses (< 10 nmol) bradykinin-induced hyperalgesia was presented by Hoe 140 but not by desArg9Leu8BK. At higher doses of bradykinin (> 100 nmol) the hyperalgesia was reduced by both Hoe 140 and desArg9Leu8BK. These data suggest that following an inflammatory insult both bradykinin B1 and B2 receptor mechanisms are involved in the accompanying hyperalgesia.

Induction of bradykinin B1 receptors in vivo in a model of ultra-violet irradiation-induced thermal hyperalgesia in the rat

1. The role of bradykinin B1 receptors in the thermal hyperalgesia following unilateral ultra-violet (u.v.) irradiation of the hindpaw of rats has been investigated. 2. In non-irradiated (naive) animals the B1 receptor agonist des-Arg9-bradykinin and bradykinin (BK) (up to 1 mumol kg-1 i.v.) had no effect on withdrawal latency to a noxious heat stimulus when administered 60 min before testing. 3. Following exposure of one hindpaw to strong u.v. irradiation the withdrawal latency of the u.v.-treated paw to radiant noxious heat fell by a maximum of 50% after 48 h. There was no reduction in latency in the contralateral paw. 4. des-Arg9-BK (1-100 nmol kg-1 i.v.) administered 24 h after u.v. exposure caused a further dose-dependent fall (50 +/- 4% reduction from saline injected animals at 100 nmol kg-1 i.v.) in withdrawal latency in the u.v.-treated paw when measured 60 min after injection. The withdrawal latency of the contralateral paw was also reduced but to a lesser extent following des-Arg9-BK (100 nmol kg-1 i.v.) with a maximum reduction of 19 +/- 3%. 5. Bradykinin also induced a further reduction in withdrawal latency (33 +/- 5% reduction at 1 mumol kg-1) although it was not as effective as des-Arg9-BK. Bradykinin did not reduce the withdrawal latency in the contralateral paw. 6. The hyperalgesic action of both des-Arg9-BK (10 nmol kg-1 i.v.) and bradykinin (100 nmol kg-1 i.v.)were antagonized by the B, receptor antagonist, des-Arg9,Leu8-BK (200 nmol kg-1 i.v.) but not by the B2 receptor antagonist, HOE 140 (0.5 .micromol kg-1 i.v.).7. The results suggest that in conditions of inflammatory hyperalgesia bradykinin B1 receptors are induced both locally and distant to the inflamed area, activation of which leads to further thermal hyperalgesia. In addition, in these conditions bradykinin appears to act predominantly via B1 receptors,presumably after degradation to des-Arg9-BK.

Antinociceptive activity of the bradykinin B1 and B2 receptor antagonists, des-Arg9, [Leu8]-BK and HOE 140, in two models of persistent hyperalgesia in the rat

There has been recent evidence linking bradykinin (BK) receptors with inflammation. This study has investigated the involvement of BK receptors in two models of persistent inflammatory hyperalgesia in rats. In a Freund's adjuvant-induced hyperalgesia model and an ultraviolet (UV)-induced hyperalgesia model in rats the specific B2 antagonist, D-Arg[Hyp3, Thi5, D-Tic7, Oic8]-BK (HOE 140), was either ineffective or weakly active in reversing hyperalgesia. The specific B1 antagonist, des-Arg9, [Leu8]-BK, was effective in reversing or preventing the development of hyperalgesia in both Freund's adjuvant-induced hyperalgesia and UV-induced hyperalgesia. The B1 agonist, des-Arg9-BK, produced a small exacerbation of hyperalgesia in both models. Data suggest that in persistent inflammatory conditions in the rat bradykinin B1 receptors are involved in the accompanying hyperalgesia.

Bradykinin receptors: pharmacological properties and biological roles

Kinins contribute to the acute inflammatory response and are implicated in the pathophysiology of inflammatory disease. The development of therapeutically viable agents that counteract the effects of kinins is, therefore, potentially very rewarding. Since kinin actions are generally mediated via an interaction with cell-surface receptors, one approach is the development of site-specific receptor antagonists. The emphasis in this review is to outline our current understanding of the properties of bradykinin receptors and the potential therapeutic applications for drugs acting at these sites. As a result of the recent introduction of potent bradykinin receptor antagonists and the cloning of bradykinin receptor genes, considerable advances in kinin research can now be confidently anticipated.

Effects of bradykinin receptor antagonists on antigen-induced respiratory distress, airway hyperresponsiveness and eosinophilia in guinea-pigs

1. We examined effects of bradykinin (BK) receptor antagonists on airway hyperresponsiveness and eosinophilia in sensitized guinea-pigs that had been administered single, as well as repeated (chronic) challenges with inhaled ovalbumin. In addition, the effects of BK antagonists on antigen-induced respiratory distress during the chronic study were noted. 2. At 24 h following single antigen challenge, guinea-pigs exhibited airway hyperresponsiveness to the bronchoconstrictor effect of i.v. histamine, characterized by a left shift in the dose-response curve. In addition, responses to the maximum dose of histamine that could be used were significantly increased in hyperresponsive guinea-pigs. The percentages of bronchoalveolar fluid, eosinophil and neutrophils also increased. 3. A BK B1 receptor antagonist, desArg9-[Leu8]-BK, significantly inhibited airway hyperresponsiveness induced by single antigen challenge. A B2 receptor antagonist, D-Arg-[Hyp3, Thi5,8,D-Phe7]-BK (NPC 349) had a small, but statistically significant inhibitory effect on responsiveness to the highest histamine dose in challenged animals. DesArg9-[Leu8]-BK significantly inhibited the neutrophilia, whereas NPC 349 inhibited infiltration by both cell types. 4. Chronic antigen challenge also caused airway hyperresponsiveness to i.v. acetylcholine (ACh), distinguished by an increase in the slope of the dose-response curve. Thus, the magnitude of the bronchoconstrictor responses to the maximum dose of ACh that could be used was significantly increased. No change in sensitivity to ACh was evident. Marked eosinophilia was also noted in the trachea, bronchi and lung parenchyma. 5. Airway hyperresponsiveness and eosinophilia, induced by chronic antigen challenge, were markedly inhibited by the B2 antagonists, D-Arg-[Hyp3,D-Phe7]-BK (NPC 567) or D-Arg-[Hyp3,Thi5d-Tic7,Tic8]-BK (NPC 16731).NPC 16731 also abolished antigen-induced cyanosis, and delayed the onset of dyspnoea,doubling the time taken for animals to exhibit respiratory distress.6. The ability of BK receptor antagonists to inhibit antigen-induced airway hyperresponsiveness, in addition to eosinophilia, indicates an important role for endogenous kinins. Moreover, the abrogation of eosinophil infiltration suggests that BK has a significant function in maintaining allergic inflammation of the airways.

Calcium signaling in endothelia: cellular heterogeneity and receptor internalization

The vasoactive factors thrombin, bradykinin (BK), and ATP are released in response to tissue damage and inflammation and act on endothelium to modulate vascular perfusion. We have investigated the second messenger response of endothelium activated by these agonists and, in particular, the mechanism of desensitization to BK. Fura-2 fluorescence ratio imaging of calf pulmonary artery endothelial cells (CPAE) revealed 5- to 10-fold increases on intracellular Ca (Cai) in response to these agents. Maximal doses caused Cai to increase from 52 to 248 nM (thrombin), 556 nM (BK), and 643 nM (ATP). Agonists elicited a rapid (within 30 s) increase of Cai due to release of Ca from intracellular stores followed by a secondary elevation of Cai dependent on entry of external Ca. The temporal characteristics of the Cai responses to all agonists were heterogeneous from cell to cell, and, interestingly, repeated stimulation gave identical signature responses from individual cells, although the amplitude of the Cai response decreased to thrombin and especially bradykinin but not for ATP. This decrease was agonist specific because ATP elicited large increases of Cai after thrombin or BK desensitization. Maximal desensitization was obtained with BK applied for 5-10 min followed by a rest of < 10 min before restimulation. Although desensitization primarily reduced the elevation of Cai due to the release of the internal store, entry of extracellular Ca was also reduced. Cells responded heterogeneously to desensitization in that those with prominent extracellular Ca entry responded most strongly upon a second stimulation with BK. Because desensitized cells still responded to ATP with an increase of Cai, the desensitization was controlled at a step prior to the activation of phospholipase C. Desensitization occurred by a reduction of BK receptor number; a 10-min BK pretreatment reduced [3H]BK binding to receptors by 70% (from 14,600 receptors/cell, Km = 5 nM, to 5,300). As surface receptor numbers decreased, internalized receptors increased as assayed by an acetic acid wash. The time course of the receptor internalization was similar to the decrease in Cai response to BK. We conclude that the vasoactive agonists thrombin, BK, and ATP increase the second messenger Cai in endothelial cells and that a desensitized Cai response occurs with BK, but not with ATP, due to downregulation and endocytosis of the BK receptor.

Functional expression of the bradykinin-B2 receptor cDNA in Chinese hamster lung CCL39 fibroblasts

The bradykinin (BK) B2 receptor cDNA was synthesized by rt-PCR and transfected into the Chinese hamster lung fibroblasts, CCL39. The CCL39 do not contain the mRNA for this receptor and do not bind BK. Clones of transfected cells were screened for BK receptor mRNA, binding of BK, and for [Ca2+]i response to BK. The clones showed various levels of receptor mRNA. Scatchard analysis of three clones, B6, B5 and B1, each gave a Kd of approximately 1.0nM while the Bmax for each clone differed at 320, 38.7, and 5.39 fmoles per 10(6) cells respectively. The [Ca2+]i response of the three clones to BK decreased with the receptor number/cell. Thus, levels of mRNA, BK binding and [Ca2+]i response proved proportionally related in the transfected clones. The actions of BK and alpha-thrombin, which has an endogenous receptor in these cells, were assessed in clone B6. BK proved active but also distinct from thrombin. BK at 10nM and thrombin at 2units/ml both effectively increased cytosolic [Ca2+]i. BK at 10nM stimulated PGE2 production three fold over basal, while thrombin only marginally elevated PGE2 levels. Alone, BK stimulated a small increase in 3H-thymidine incorporation into DNA. However, in combination with insulin, BK stimulated DNA synthesis to 76% of thrombin, a potent mitogen in these cells. These results illustrate that the BK-B2 receptor cDNA can be stably transfected into a mammalian cell and can activate transmembrane signalling pathways.

Recent developments in the understanding of bradykinin receptors

The dramatic activities of bradykinin and related peptides as mediators of pain, inflammation and hypotension have been intensely studied for several decades. More recently, the involvement of bradykinin in regulation of ion transport by epithelia, hormone release from endocrine organs, energy metabolism, tissue growth, and leukocyte activation have become topics of study. Kininogen precursors, synthetic kallikreins, and degradative kininases have been characterized in detail with regard to catalytic mechanisms, physical structure and gene regulation; however, the actual receptors for bradykinin are still only poorly understood. This situation is caused by the lack of availability of potent, specific receptor antagonists. However, specific bradykinin receptor antagonists became available in 1985, and several very potent classes of agents are now available; also, the first bradykinin receptor has been cloned.

Bradykinin receptor antagonists

Bradykinin and its active metabolites are produced at the sites of their actions by kallikreins. They potently elicit a variety of biological effects: hypotension, bronchoconstriction, gut and uterine contraction, epithelial secretion in airway, gut, and exocrine glands, vascular permeability, pain, connective tissue proliferation, and eicosanoid formation. These effects are mediated by at least two broad classes of receptors. The most common is the B2 subtype. The Stewart and Vavrek peptides characterized by a DPhe7 substitution have provided powerful tools for study of bradykinin's actions by competitively and specifically blocking bradykinin B2 receptors. The significance of kinins in certain human diseases is being explored using these new tools and potential therapeutic agents. At present, human clinical trials are underway to test the usefulness of bradykinin receptor antagonists in the symptoms of the common cold and in the pain associated with severe burns. Trials for use in asthma will be initiated in 1990.

Kinins act on B1 or B2 receptors to release conjointly endothelium-derived relaxing factor and prostacyclin from bovine aortic endothelial cells

1. Bradykinin (Bk) induced the coupled release of endothelium-derived relaxing factor (EDRF) and prostacyclin (PGI2) from bovine aortic endothelial cells grown in culture. The B2 kinin receptor antagonist, [D-Arg0,Hyp3,Thi5,8,D-Phe7]-Bk, abolished this release by Bk. 2. Des-Arg9-Bk, a B1 kinin receptor agonist, also induced the release of EDRF and PGI2, but much higher concentrations were required to obtain a similar release to that induced by Bk. 3. [Leu8],des-Arg9-Bk, a B1 receptor antagonist, significantly reduced the response to des-Arg9-Bk without affecting the release induced by Bk. 4. The release of EDRF and PGI2 induced by arachidonic acid or ADP was not significantly affected by the B2 or the B1 antagonist. 5. We conclude, therefore, that Bk and des-Arg9-Bk were acting respectively on B2 and B1 bradykinin receptors. 6. The possible role of kinin receptors in the release of EDRF and PGI2 from endothelial cells is discussed.