Biphasic response to bradykinin in isolated porcine iliac arteries is mediated by bradykinin B1 and B2 receptors

Interaction of Angiotensin-(1-7) with kinins in the kidney circulation: Role of B1 receptors

Changes in renal hemodynamics impact renal function during physiological and pathological conditions. In this context, renal vascular resistance (RVR) is regulated by components of the Renin-Angiotensin System (RAS) and the Kallikrein-Kinin System (KKS). However, the interaction between these vasoactive peptides on RVR is still poorly understood. Here, we studied the crosstalk between angiotensin-(1-7) and kinins on RVR. The right kidneys of Wistar rats were isolated and perfused in a closed-circuit system. The perfusion pressure and renal perfusate flow were continuously monitored. Ang-(1-7) (1.0-25.0 nM) caused a sustained, dose-dependent reduction of relative RVR (rRVR). This phenomenon was sensitive to 10 nM A-779, a specific Mas receptor (MasR) antagonist. Bradykinin (BK) promoted a sustained and transient reduction in rRVR at 1.25 nM and 125 nM, respectively. The transient effect was abolished by 4 μM des-Arg9-Leu8-bradykinin (DALBK), a specific kinin B1 receptor (B1R) antagonist. Accordingly, des-Arg9-bradykinin (DABK) 1 μM (a B1R agonist) increased rRVR. Interestingly, pre-perfusion of Ang-(1-7) changed the sustained reduction of rRVR triggered by 1.25 nM BK into a transient effect. On the other hand, pre-perfusion of Ang-(1-7) primed and potentiated the DABK response, this mechanism being sensitive to A-779 and DALBK. Binding studies performed with CHO cells stably transfected with MasR, B1R, and kinin B2 receptor (B2R) showed no direct interaction between Ang-(1-7) with B1R or B2R. In conclusion, our findings suggest that Ang-(1-7) differentially modulates kinin's effect on RVR in isolated rat kidneys. These results help to expand the current knowledge regarding the crosstalk between the RAS and KKS complex network in RVR.

Vasomotor effects of 5-hydroxytryptamine, histamine, angiotensin II, acetylcholine, noradrenaline, and bradykinin on the cerebral artery of bottlenose dolphin (Tursiops truncatus)

From an evolutionary aspect, dolphins share a very close phylogenetic relationship with pigs. Previously, we characterized porcine cerebral artery responsiveness to intrinsic vasoactive substances. Therefore, here, we investigated dolphin (Tursiops truncatus) cerebral artery responsiveness to 5-hydroxytryptamine (5-HT), histamine (His), angiotensin (Ang) II, acetylcholine (ACh), noradrenaline (NA), and bradykinin (BK) to characterize their related receptor subtypes. We also compared dolphin cerebral artery responsiveness with porcine cerebral artery responsiveness. We found that 5-HT and His induced concentration-dependent contraction of the dolphin cerebral artery. Ketanserin (a 5-HT₂ antagonist) and methiothepin (a 5-HT₁ and 5-HT₂ antagonist) shifted the concentration-response curve for 5-HT to the right. Although diphenhydramine (an H₁ antagonist) shifted the concentration-response curve for His to the right, cimetidine (an H₂ antagonist) had no such effect. Ang II and ACh did not produce any vasomotor actions. NA induced concentration-dependent relaxation. Propranolol (a β antagonist) shifted the concentration-response curve for NA to the right, whereas phentolamine (an α antagonist) had no significant effect. BK induced relaxation followed by contraction in pre-contracted arteries with intact endothelium. HOE140 (a B₂ antagonist) shifted the concentration-response curve for BK to the right, whereas des-Arg⁹-[Leu⁸]-BK (a B₁ antagonist) had no significant effect. These results suggest that 5-HT₁, 5-HT₂, and H₁ receptor subtypes are important in arterial contraction and that β and B₂ receptor subtypes modify these contractions to relaxations. The responsiveness of the dolphin cerebral artery is very similar to that of porcine cerebral artery, supporting their evolutionary linkage.

COX-2 mediated induction of endothelium-independent contraction to bradykinin in endotoxin-treated porcine coronary artery

This study examined the vascular effects of bradykinin in health and vascular inflammation comparing responses of isolated pig coronary arteries in the absence and presence of endotoxins. Bradykinin induced contractions in lipopolysaccharide-treated, but not untreated, arterial rings without endothelium. The B2-receptor antagonist HOE140, but not the B1-receptor inhibitor SSR240612, blocked these endothelium-independent contractions in response to bradykinin. The bradykinin-induced contractions were blocked by indomethacin, celecoxib, and terbogrel but not valeryl salicylate, AH6809, AL 8810, or RO1138452. They were attenuated by N-(p-amylcinnamoyl) anthranilic acid, and by diethyldithiocarbamate plus tiron but not by L-NAME. Quantitative reverse-transcription polymerase chain reaction revealed significant upregulations of messenger RNA expressions of B1 receptors, COX-2, and thromboxane A synthase 1 (TBXAS1) following lipopolysaccharide incubation but not of B2 receptors or COX-1. The present data demonstrate that bradykinin induces contractions mediated by the COX-2 pathway in endotoxin-treated pig coronary arteries. These results support differential roles of bradykinin in health and disease.

Kinins and neuroinflammation: Dual effect on prostaglandin synthesis

The role of kinins, well known as peripheral inflammatory mediators, in the modulation of brain inflammation is unclear. The present data show that bradykinin, a bradykinin B(2) receptor agonist, enhanced both basal and lipopolysaccharide-induced prostaglandin E(2) synthesis in rat neonatal glial cells in culture. By contrast, Lys-des-Arg(9)-bradykinin, which is a kinin breakdown product and a selective bradykinin B(1) receptor agonist, attenuated both basal and lipopolysaccharide-induced production of prostaglandin E(2) in glia. These results suggest a feedback regulatory mechanism of kinins on glial cells, in which prostaglandin synthesis is initially enhanced by bradykinin (B(2)) and eventually blocked by the effect of the kinin breakdown product, acting on bradykinin B(1) receptors.

Coronary vasomotor response to the selective B1-kinin-receptor agonist Des-Arg9-bradykinin in humans

OBJECTIVES

The aim of the present study was to assess the effects of selective B1-receptor stimulation with des-Arg9-bradykinin on coronary vasomotion in transplanted and non-transplanted patients.

BACKGROUND

Bradykinin B1-receptors have been identified on endothelial and smooth muscle cells in human coronary arteries in vitro; however, their physiologic role in the coronary circulation is unknown.

METHODS

Twelve heart transplant patients were compared with 10 control subjects at 3.2 +/- 2.2 months after surgery. Coronary flow velocity was measured using guide-wire Doppler. The diameter of 3 epicardial segments of the left coronary artery and coronary blood flow were assessed at baseline, immediately after infusions of increasing doses of des-arginine(Arg9)-bradykinin at estimated coronary blood concentrations of 5.4 x 10(-9), 5.4 x 10(-8), 5.4 x 10(-7) and 1.6 x 10(-6) mol/liter, and of acetylcholine at 10(-8), 10(-7) and 10(-6) mol/liter).

RESULTS

Des-Arg9-bradykinin induced a similar decrease in all measured epicardial diameters in both groups and no change in coronary blood flow. Vasoconstriction was significant only at the 2 highest concentrations: -6 +/- 9% (p < 0.01) and -7 +/- 11% (p < 0.01) in control subjects, and -8 +/- 8% (p < 0.001) and -9 +/- 11% (p < 0.001) in heart transplant patients. Acetylcholine induced significant epicardial vasodilation in control subjects and vasoconstriction in transplant patients. The presence of allograft rejection did not modify the responses to des-Arg9-bradykinin with regard to both conductance and resistance vessels.

CONCLUSIONS

Kinin B1-receptors exist and can be stimulated in humans. The vasoconstrictive action on epicardial coronary arteries of des-Arg(9)-bradykinin in humans argues for a predominant action of B1-receptor stimulation at the level of smooth muscle cells.

Effect of Panax ginseng extract (G115) on angiotensin-converting enzyme (ACE) activity and nitric oxide (NO) production

This study investigates the effects of the Panax ginseng (Araliaceae) extract G115 on angiotensin-converting enzyme (ACE) activity and nitric oxide (NO) in cultured human endothelial cells from umbilical veins (HUVEC) and bovine mesenteric arteries (BMA). In HUVEC, ACE activity was significantly reduced after 10 min incubation with aqueous extract of ginseng 5.0 and 10 mg/ml. This effect was additative with the inhibition of the traditional ACE inhibitor enalaprilat. No effect was seen on NO production from the cells. Angiotensin I-induced contraction of BMA was significantly attenuated by 0.1 and 0.5 mg/ml ginseng, while no endothelium-dependent or -independent relaxation was seen. In conclusion, extract of Panax ginseng (G115) inhibits ACE activity, but does not affect NO production in HUVEC and BMA.

Different Prostanoids Are Involved in Bradykinin-Induced Endothelium-Dependent and -Independent Vasoconstriction in Rat Mesenteric Resistance Arteries

Mechanisms underlying bradykinin-induced vasoconstriction were investigated in rat perfused mesenteric vascular beds with active tone. In preparations with intact endothelium, bolus injections of bradykinin (1 to 1,000 pmol) dose-dependently produced three-phase vascular effects, which consisted of a first-phase vasodilation followed by a second-phase vasoconstriction and a subsequent third-phase vasodilation; these effects were abolished by FR172357 (bradykinin B(2)-receptor antagonist), but not by des-Arg(9)-[Leu(8)]-bradykinin (bradykinin B(1)-receptor antagonist). In preparations with intact endothelium, indomethacin (cyclooxygenase inhibitor), seratrodast (thromboxane A(2) (TXA(2))-receptor antagonist), ONO-3708 (TXA(2)/prostaglandin H(2) (PGH(2))-receptor antagonist) or ozagrel (TXA(2) synthesis inhibitor) markedly inhibited the bradykinin-induced vasoconstriction. In preparations without endothelium, the bradykinin-induced vasoconstriction was abolished by indomethacin and ONO-3708, while seratrodast and ozagrel had no effect. These results suggest that the endothelium-dependent vasoconstriction of bradykinin is mainly mediated by TXA(2) and that prostanoids other than TXA(2), probably PGH(2), in mesenteric vascular smooth muscle are responsible for bradykinin-induced endothelium-independent vasoconstriction.

Study of the mechanisms involved in the bradykinin-induced contraction of the pig iris sphincter muscle in vitro

This study was designed to investigate the mechanisms by which bradykinin induces contraction of the pig iris sphincter muscle in vitro. Addition of bradykinin, Lys-bradykinin and Met-Lys-bradykinin to the pig iris sphincter resulted in a graded contraction with a mean EC(50s) of 21, 11 and 5 nM, respectively. The bradykinin B(1) receptor agonist des-Arg(9)-bradykinin only caused a slight contraction, measured 6 h after the tissue was set up. The B(2) receptor antagonists FR 173657 ((E)-3-(6-acetamido-3-pyridyl)-N [N-2-4-dichloro-3-[(2-methyl-8-quinolinyl) oxymethyl] phenyl]-N-methylamino-carbonyl-ethyl] acrylamide) and Hoe 140 (D-Arg(0)-[Hyp(3), Thi(5), D-Tic(7), Oic(8)]-bradykinin produced a graded shift to the right associated with marked inhibition of the bradykinin-induced contraction. Atropine, guanethidine or tetrodotoxin significantly reduced the bradykinin-induced contraction. Dazoxiben, an inhibitor of thromboxane A(2), and MK-571 (3-(3-(2-(7-chloro-2-quinolinyl) ethenyl) phenyl ((3-dimethyl amino-3oxo-propyl) thio) methyl) propanoic acid, a leukotriene D(4) receptor-selective antagonist, also caused inhibition of the bradykinin-mediated contraction. Cyclooxygenase-1 and -2 inhibitors, indomethacin, ibuprofen, valeryl salicylate and NS 398 (N-[2-(cyclohexyloxy)-4-nitrophenyl]methanosulfonamide) all significantly inhibited the bradykinin-mediated contraction without affecting the carbachol-induced contraction of the pig iris sphincter. Taken together, these results indicate that the bradykinin-mediated contraction of the pig iris sphincter muscle seems to be mediated primarily by the activation of the B(2) receptor release of acetylcholine, noradrenaline and both cyclooxygenase-1 and -2 metabolites besides the release of leukotriene D(4) and tromboxane A(2) from the arachidonic acid pathway.

Effect of gender on endothelium-dependent dilation to bradykinin in human adipose microvessels

We examined the influence of gender and climacteric status, two coronary risk factors, on bradykinin (BK)-induced dilation in adipose arterioles from men and women of different ages [premenopausal women (Pre-W), postmenopausal women (Post-W), and similar aged men (Y-M and O-M), respectively]. We examined the responses from both omental (more closely associated with coronary disease) and subcutaneous fat. Tissues were obtained at surgery and cannulated (60 mmHg) for measurement of internal diameter. In vessels from omental tissue, dilation to BK was more sensitive in Pre-W than other groups, whereas in vessels from subcutaneous tissue, sensitivity to BK was greater in both Pre-W and Post-W compared with Y-M and O-M. Maximal dilation was similar among groups. Indomethacin (Indo; 10(-5) M) alone had no effect on dilation to BK in any groups, but Indo and N(omega)-nitro-L-arginine methyl ester (L-NAME; 10(-4) M) reduced dilation to BK in Pre-W more than in Y-M. L-NAME increased dilation to BK in subcutaneous fat from Y-M but had no effect in Post-W and O-M. Indo- and L-NAME-resistant dilation in all vessels was markedly reduced by 30 mM KCl. There was no difference in sodium nitroprusside-induced dilation among groups. We conclude that gender and climacteric state contribute to mechanisms of microvascular regulation in humans. Functional vascular differences in visceral and subcutaneous fat may underlie the proposed differential influence of these tissues on cardiovascular risk.

Bradykinin enhances in vitro procoagulant and antifibrinolytic properties of rat vascular endothelial cells

INTRODUCTION

Bradykinin (BK) is a biologically active peptides that exerts a broad spectrum of pathophysiological effects mainly by producing nitric oxide (NO) and prostacyclin from vascular endothelial cells. A direct effect of BK on vascular endothelial cells regarding the expression of the regulatory proteins of coagulation and fibrinolysis has not been fully elucidated.

MATERIALS AND METHODS

The effects of BK on the expression of tissue factor (TF), tissue factor pathway inhibitor (TFPI), plasminogen activator inhibitor-1 (PAI-1), and tissue-type plasminogen activator (TPA) in cultured rat aortic endothelial cells (RAECs) were respectively evaluated by Northern blot and chromogenic assay or enzyme-linked immunosorbent assay (ELISA).

RESULTS

BK significantly increased the expression of TF and PAI-1 in both mRNA and protein levels, but it did not affect the expression of TFPI. Although BK tended to increase TPA mRNA expression, the observed increase was not statistically significant. Those effects are considered to be mediated by B(2) receptor, because B(2) receptor antagonist (Hoe 140) suppressed those mRNA inductions by BK. Furthermore, since those mRNA inductions by BK were enhanced by nitro-L-arginine-methyl ester (L-NAME) and attenuated by L-arginine (L-Arg), NO was speculated to negatively contribute to the expressions of TF and PAI-1.

CONCLUSION

BK was indicated to modify the property of vascular endothelial cells to be procoagulant and antifibrinolytic. Those effects of BK were considered to be the net of its direct effect and the effect negatively mediated by NO.

Contribution of cytochrome P450 metabolites to bradykinin-induced vasodilation in endothelial NO synthase deficient mouse hearts

We have characterized the contribution of endothelial nitric oxide synthase (eNOS), cyclo-oxygenase (COX) and cytochrome P450 (CYP450) to the bradykinin (BK)- induced vasodilation in isolated hearts from wildtype (WT) and eNOS deficient mice (eNOS-/-). The endothelium-dependent vasodilation by bradykinin (BK, 1 microM) was significantly lower in eNOS-/- hearts than that in WT hearts (+247% and +325% of basal flow, respectively), while there was no difference in the endothelium-independent vasodilation by adenosine. In WT hearts, the BK-induced vasodilation was markedly attenuated following inhibition of NOS with ETU (10 microM) but not after COX inhibition with diclofenac (3 microM) (P<0.01). In line with this finding, Bk did not increase the cardiac prostacyclin release as measured by ELISA for 6-keto-PGF1alpha in the coronary venous effluent. In eNOS-/- hearts, the flow response to BK was insensitive to both NOS and COX inhibition. The NOS/COX-independent vasodilatory factor which remained under L-NMMA+DF application was almost completely eliminated by either clotrimazole (3 microM), miconazole (0.5 microM) or 17-ODYA (1 microM), suggesting that it was a metabolite of CPY450 enzymes. Sulfaphenazole (10 microM), a CYP450 2C inhibitor, exerted only a minimal inhibitory effect. In eNOS-/- hearts the effect of CYP450 inhibitors on the BK response was significantly more pronounced than in WT hearts, indicating an enhanced contribution of CYP450 enzymes. These findings suggest that in isolated mouse hearts the BK-induced vasodilation is mediated by NO and CYP450 metabolites but not by prostaglandins. The CYP450 dependent vasodilator was was functionally up-regulated in eNOS-/- hearts and thus likely to compensate for the loss of eNOS in the coronary circulation.

Triphasic vascular responses to bradykinin in the mesenteric resistance artery of the rat

The vascular effects of bradykinin were studied in rat perfused mesenteric vascular beds with active tone. Bolus injections of bradykinin (1-1000 pmol) but not des-Arg(9)-bradykinin (bradykinin B(1) receptor agonist) induced triphasic vascular responses: the initial sharp vasodilation followed by transient vasoconstriction and subsequent gradual vasodilation. The triphasic vascular responses to bradykinin were abolished by FR 172357 (3-bromo-8-[2,6-dichloro-3-[N-[(E)-4-(N,N-dimethylcarbamoyl) cinnamidoacetyl]-N-methylamino]benzyloxy]-2-metylimidazo[1,2-a]pyridine) (bradykinin B(2) receptor antagonist, 0.1 microM). Endothelium removal with sodium deoxycholate and N(w)-nitro-L-arginine (300 microM) abolished the bradykinin-induced initial sharp vasodilation. Indomethacin (0.5 microM) and seratrodast (thromboxane A(2) receptor antagonist, 0.5 and 5 microM) abolished the bradykinin-induced second vasoconstriction. The bradykinin-induced third vasodilation was abolished by capsaicin (1 microM) and calcitonin gene-related peptide (CGRP)-(8-37) (CGRP receptor antagonist, 0.5 microM). These findings suggest that the bradykinin-induced initial sharp vasodilation is endothelium dependent, that endogenous thromboxane A(2) is involved in the second vasoconstriction, and that the third slow vasodilation is produced by activation of capsaicin-sensitive CGRP-containing nerves.

Bradykinin causes endothelium-independent hyperpolarisation and neuromodulation by prostanoid synthesis in hamster mesenteric artery

The mechanism of bradykinin-induced hyperpolarisation and purinergic neuromodulation was examined in the hamster superior mesenteric artery using intracellular microelectrode techniques. Bradykinin induced a concentration-dependent hyperpolarisation both in endothelium-intact and -denuded preparations. Indomethacin blocked this hyperpolarisation. Prostacyclin and iloprost also hyperpolarised the membrane of mesenteric artery, while prostaglandin E(2) did not evoke any membrane hyperpolarisation. The bradykinin-, prostacyclin- and iloprost-induced hyperpolarisation were inhibited by glibenclamide. Bradykinin also inhibited the amplitude of the purinergic excitatory junction potentials (e.j.p.s), both in endothelium-intact and -denuded preparations. Indomethacin blocked this inhibitory effect. Prostaglandin E(2) inhibited the e.j. p. in a concentration-dependent manner. Focally applied ATP-induced depolarisation was not modified by bradykinin or prostaglandin E(2.) These findings suggest that bradykinin via prostanoids production pre-synaptically, inhibit the amplitude of purinergic e.j.p., resulting inhibitory purinergic neuromodulation. In addition, bradykinin-released prostanoids elicits membrane hyperpolarisation of smooth muscle cells through opening of K(ATP) channels.

Integrative effects of nitric oxide and endothelium-derived hyperpolarizing factor induced by acetylcholine and bradykinin in rat hindquarter perfusion

We investigated the roles of endothelium-derived vasodilative factors in rat hindquarter perfusion using a system for the direct measurement of nitric oxide (NO). Acetylcholine (ACh) induced the dose-dependent release of NO with a concomitant decrease in perfusion pressure. Under the influence of N(G)-monomethyl-l-arginine (l-NMMA), NO release in response to ACh was blocked, while the perfusion pressure still decreased. In the presence of tetraethylammonium (TEA), the decrease in perfusion pressure in response to ACh was attenuated compared to the control value. The decrease in perfusion pressure in response to ACh was almost abolished in the presence of both l-NMMA and TEA or with deendothelialization. Bradykinin (BK) also induced NO release and biphasic effects on the perfusion pressure. The perfusion pressure decreased with a lower concentration of BK and increased with a higher concentration. l-NMMA and TEA each abolished the decrease in perfusion pressure induced by BK. Furthermore, in the presence of both l-NMMA and TEA, the perfusion pressure actually increased in response to BK. These results suggest that ACh and BK induce vasodilation through NO release and a potassium channel dependent mechanism via endothelium.

Simultaneously increased TxA(2) activity in isolated arterioles and platelets of rats with hyperhomocysteinemia

We aimed to elucidate the effect of hyperhomocysteinemia (HHcy) on the synthesis of prostaglandins in rat skeletal muscle arterioles and platelets. Male Wistar rats were divided into 2 groups: (1) control rats, with plasma Hcy levels of 6.5+/-0.5 micromol/L (n=50) and (2) rats with HHcy, induced by daily intake of 1 g/kg body weight methionine in the drinking water for 4 weeks (plasma Hcy levels were 20.6+/-3.0 micromol/L, P<0.01 versus controls; n=50). Arterioles (diameter approximately 130 micrometer) were isolated from the gracilis muscle, cannulated, and pressurized (at 80 mm Hg), and changes in their diameters were followed by video microscopy. Constrictions to bradykinin (BK; 10(-10) to 10(-7) mol/L) were significantly greater in HHcy than in control rat arterioles (at 10(-9) mol/L BK, changes were 11+/-3% in control and 41+/-9% in HHcy rats). The cyclooxygenase inhibitor indomethacin (10(-5) mol/L), the prostaglandin H(2)/thromboxane A(2) (PGH(2)/TxA(2)) receptor antagonist SQ 29,548 (10(-6) mol/L), or the TxA(2) synthase inhibitor furegrelate (5x10(-6) mol/L) significantly decreased constrictions to BK in both groups but more so in HHcy arterioles, thus eliminating the difference between responses of HHcy and control arterioles. Constrictions to U46619 (a TxA(2) analogue) were significantly greater in HHcy than in control arterioles (at 10(-8) mol/L U46619, values for controls were 33+/-2% and 54+/-3% for HHcy). Endothelium removal or indomethacin treatment attenuated constrictions to U46619 in HHcy arterioles and eliminated the difference in responses. Also, aggregation of platelets from HHcy rats to collagen and ADP was significantly enhanced compared with controls (with 5 microgram/mL collagen: controls, 23+/-5%; HHcy, 49+/-5%; with 10(-7) mol/L ADP: controls, 25+/-3%; HHcy, 35+/-3%). Indomethacin or SQ 29,548 caused greater inhibition of aggregation of HHcy platelets compared with controls, thereby eliminating the differences between the 2 groups. Thus, HHcy enhances TxA(2) synthesis both in the arteriolar endothelium and platelets. By promoting vascular constriction and platelet aggregation simultaneously, these alterations are likely to contribute to the atherothrombotic vascular diseases described in HHcy.

The mechanism of bradykinin-induced endothelium-dependent contraction and relaxation in the porcine interlobar renal artery

The mechanism of endothelium-dependent regulation of vascular tone of bradykinin was investigated by simultaneously monitoring the changes in the cytosolic Ca(2+) concentration and the force of smooth muscle in fura-2-loaded strips of the porcine renal artery with endothelium. During phenylephrine-induced sustained contraction, bradykinin (>3x10(-9) M) caused endothelium-dependent triphasic changes in the force of the strips, composed of an initial relaxation, a subsequent transient contraction and a late sustained relaxation. At low concentrations (10(-10) - 10(-9) M), bradykinin caused an endothelium-dependent biphasic relaxation with no contraction. A thromboxane A(2) (TXA(2))/prostaglandin H(2) (PGH(2)) receptor antagonist (10(-5) M ONO-3708) completely inhibited, while a TXA(2) synthase inhibitor (10(-5) M OKY-046) only partially inhibited, the transient contraction induced by bradykinin. Under conditions where the bradykinin-induced contraction was inhibited by ONO-3708 during the phenylephrine-induced contraction, bradykinin induced only a transient relaxation in the presence of N(Omega)-nitro-L-arginine methyl ester (L-NAME). This transient relaxation was inhibited when the precontraction was initiated by phenylephrine plus 40 mM extracellular K(+). The removal of L-NAME from this condition caused a partial reappearance of the initial relaxation and a complete reappearance of the sustained relaxation. In conclusion, bradykinin caused the endothelium-dependent triphasic regulation of vascular tone in the porcine renal artery. The concentrations of bradykinin required to induce a contraction was higher than that required to induce relaxation. Both TXA(2) and PGH(2) were involved in the bradykinin-induced contraction. The initial relaxation was mediated by nitric oxide and hyperpolarizing factors while the sustained relaxation depended on nitric oxide.

Nitric oxide modulates captopril-mediated angiotensin-converting enzyme inhibition in porcine iliac arteries

The influence of the angiotensin-converting enzyme inhibitor captopril on bradykinin-and angiotensin I-induced responses with special regard to nitric oxide (NO) was studied. Auxometric tension and angiotensin-converting enzyme activity was studied in isolated porcine iliac arteries. Captopril potentiated bradykinin-induced contraction of preparations with intact endothelium; this potentiation was not seen with the kininase I inhibitor mergepta or a bradykinin B(1)-receptor antagonist. Captopril did not affect bradykinin-induced relaxation. The captopril-mediated increase of bradykinin-induced contraction was only seen in preparations with intact endothelium, while captopril did not affect arterial strips treated with Nomega-nitro-L-arginine. Angiotensin I-induced contractions was less reduced by captopril when the strips were pretreated with Nomega-nitro-L-arginine. Both captopril and the NO donor S-nitroso-N-acetyl-penicillamine inhibited angiotensin-converting enzyme activity. An additional reduction in angiotensin-converting enzyme activity was seen when S-nitroso-N-acetyl-penicillamine was added to captopril-treated preparations. In conclusion, captopril increased bradykinin-induced contraction in a NO-dependent manner. This potentiation is probably mediated by the increased metabolism of bradykinin by kininase I, and the additive angiotensin-converting enzyme inhibitory effect of captopril and NO.

Stimulation of bradykinin B2-receptors on endothelial cells induces relaxation and contraction in porcine basilar artery in vitro

1. The aim of the present study was to characterize the subtypes of bradykinin (BK) receptors that evoke the relaxation and contraction induced by BK and to identify the main contracting and relaxing factors in isolated porcine basilar artery by measuring changes in isometric tension and a thromboxane (TX) metabolite. 2. Endothelial denudation completely abolished both responses. [Thi5,8, D-Phe7]-BK (a B2-receptor antagonist) inhibited the BK-induced relaxation and contraction, whereas des-Arg9, [Leu8]-BK (a B1-receptor antagonist) had no effect. 3. L-nitro-arginine (L-NA, a nitric oxide synthase inhibitor) completely inhibited BK-induced relaxation. Indomethacin (a cyclo-oxygenase inhibitor) completely and ONO-3708 (a TXA2/prostaglandin H2 receptor antagonist) partially inhibited BK-induced contraction, whereas OKY-046 (a TXA2 synthase inhibitor) and nordihydroguaiaretic acid (a lipoxygenase inhibitor) did not. 4. In the presence of L-NA, the contractile response to BK was inhibited by indomethacin or ONO-3708 and was competitively antagonized by [Thi5,8, D-Phe7]-BK (pA2=7.50). In the presence of indomethacin, the relaxant response to BK was inhibited by L-NA and was competitively antagonized by [Thi5,8, D-Phe7]-BK (pA2=7.59). 5. TXA2 release was not induced by BK-stimulation. 6. These results suggest that the endothelium-dependent relaxation and contraction to BK in the porcine basilar artery is mediated via activation of endothelial B2-receptors. The main relaxing factor may be NO and the main contracting factor may be prostaglandin H2.