Kinins in the cardiovascular system

Effects of Bradykinin B2 Receptor Ablation from Tyrosine Hydroxylase Cells on Behavioral and Motor Aspects in Male and Female Mice

The kallikrein-kinin system is a versatile regulatory network implicated in various biological processes encompassing inflammation, nociception, blood pressure control, and central nervous system functions. Its physiological impact is mediated through G-protein-coupled transmembrane receptors, specifically the B1 and B2 receptors. Dopamine, a key catecholamine neurotransmitter widely distributed in the CNS, plays a crucial role in diverse physiological functions including motricity, reward, anxiety, fear, feeding, sleep, and arousal. Notably, the potential physical interaction between bradykinin and dopaminergic receptors has been previously documented. In this study, we aimed to explore whether B2R modulation in catecholaminergic neurons influences the dopaminergic pathway, impacting behavioral, metabolic, and motor aspects in both male and female mice. B2R ablation in tyrosine hydroxylase cells reduced the body weight and lean mass without affecting body adiposity, substrate oxidation, locomotor activity, glucose tolerance, or insulin sensitivity in mice. Moreover, a B2R deficiency in TH cells did not alter anxiety levels, exercise performance, or motor coordination in female and male mice. The concentrations of monoamines and their metabolites in the substantia nigra and cortex region were not affected in knockout mice. In essence, B2R deletion in TH cells selectively influenced the body weight and composition, leaving the behavioral and motor aspects largely unaffected.

Amelioration of cardiac function and activation of anti-inflammatory vasoactive peptides expression in the rat myocardium by low level laser therapy

Low-level laser therapy (LLLT) has been used as an anti-inflammatory treatment in several disease conditions, even when inflammation is a secondary consequence, such as in myocardial infarction (MI). However, the mechanism by which LLLT is able to protect the remaining myocardium remains unclear. The present study tested the hypothesis that LLLT reduces inflammation after acute MI in female rats and ameliorates cardiac function. The potential participation of the Renin-Angiotensin System (RAS) and Kallikrein-Kinin System (KKS) vasoactive peptides was also evaluated. LLLT treatment effectively reduced MI size, attenuated the systolic dysfunction after MI, and decreased the myocardial mRNA expression of interleukin-1 beta and interleukin-6 in comparison to the non-irradiated rat tissue. In addition, LLLT treatment increased protein and mRNA levels of the Mas receptor, the mRNA expression of kinin B2 receptors and the circulating levels of plasma kallikrein compared to non-treated post-MI rats. On the other hand, the kinin B1 receptor mRNA expression decreased after LLLT. No significant changes were found in the expression of vascular endothelial growth factor (VEGF) in the myocardial remote area between laser-irradiated and non-irradiated post-MI rats. Capillaries density also remained similar between these two experimental groups. The mRNA expression of the inducible nitric oxide synthase (iNOS) was increased three days after MI, however, this effect was blunted by LLLT. Moreover, endothelial NOS mRNA content increased after LLLT. Plasma nitric oxide metabolites (NOx) concentration was increased three days after MI in non-treated rats and increased even further by LLLT treatment. Our data suggest that LLLT diminishes the acute inflammation in the myocardium, reduces infarct size and attenuates left ventricle dysfunction post-MI and increases vasoactive peptides expression and nitric oxide (NO) generation.

Pharmacological analysis of the rat femoral artery response to bradykinin

Bradykinin (BK) plays an important role in different physiological processes including the general preservation and modulation of vascular systems. The present study was designed in order to examine the effect of BK on isolated rat femoral artery rings and to investigate the participation of intact endothelium, cyclooxygenase products, Ca²⁺ channels, Na⁺/K⁺–ATPase, and B₂ kinin receptors in BK-induced action. Circular artery segments were placed in organ baths. The endothelium was mechanically removed from some arteries. Concentration–contraction curves for BK were obtained in the rings previously equilibrated at the basal tone. BK produced a concentration–dependent contraction, which was reduced by endothelial denudation. The BK–induced effect was almost completely inhibited by indomethacin (cyclooxygenase inhibitor) or OKY–046 (thromboxane A₂–synthase inhibitor). Nifedipine (Ca²⁺ channel blocker), ouabain (Na⁺/K⁺–ATPase inhibitor), or HOE–140 (selective B₂ kinin receptor antagonist) significantly reduced the BK–evoked effect. In conclusion, it can be proposed that BK produces concentration– and endothelium–dependent contractions of the isolated rat femoral artery, which is for the most part a consequence of B₂ kinin receptor activation. Cyclooxygenase contractile products, especially thromboxane A₂, play a significant role in this course of action. The transduction mechanism involved in the process of BK–induced femoral artery contraction include the activation of voltage–gated Ca²⁺ channels, and in a smaller extent Na⁺/K⁺–ATPase as well.

Association of the human bradykinin B2 receptor gene with chronic renal failure

INTRODUCTION

The kallikrein-kinin system plays an important role in blood pressure homeostasis and renal sodium regulation, and some studies have reported that the kinins have a protective effect against hypertension and the development of renal disease. The B2-bradykinin receptor (B2R) mediates the majority of physiological actions of bradykinin. We investigated the effect of the C181-->T polymorphism in exon 2 of the B2R gene in patients with end-stage renal disease (ESRD).

METHODS

This study involved 790 patients with ESRD and 510 healthy controls. All participants were genotyped for the B2R C181-->T polymorphism by PCR followed by digestion of a PCR product with TaqI restriction endonuclease. DNA fragments were separated by agarose gel electrophoresis. Genotype and allele frequencies were compared between the groups. All calculations were performed using SPSS 5.0 for Windows.

RESULTS

B2R genotype distribution in patients and controls was in accordance with Hardy-Weinberg equilibrium. The frequency of the T allele was higher in ESRD patients than in controls. The significant difference was observed in the age at onset of renal disease; for patients with the T allele the mean age at onset was 36.8 years, compared with 52.4 years for those carrying only the C allele (p<0.001). The frequencies of the T allele and carrier genotypes were not associated with gender, presence of hypertension, or underlying kidney disease.

CONCLUSION

Our results suggest that the B2R polymorphism has a potential role in the earlier development of chronic renal failure in susceptible individuals. We did not confirm the previously published reports that the B2R gene polymorphism has a protective role in the development of ESRD.

Extracellular and intracellular proteases in cardiac dysfunction due to ischemia-reperfusion injury

Various procedures such as angioplasty, thrombolytic therapy, coronary bypass surgery, and cardiac transplantation are invariably associated with ischemia-reperfusion (I/R) injury. Impaired recovery of cardiac function due to I/R injury is considered to be a consequence of the occurrence of both oxidative stress and intracellular Ca(2+)-overload in the myocardium. These changes in the ischemic myocardium appear to activate both extracellular and intracellular proteases which are responsible for the cleavage of extracellular matrix and subcellular structures involved in the maintenance of cardiac function. It is thus intended to discuss the actions of I/R injury on several proteases, with a focus on calpain, matrix metalloproteinases, and cathepsins as well as their role in inducing alterations both inside and outside the cardiomyocytes. In addition, modifications of subcellular organelles such as myofibrils, sarcoplasmic reticulum and sarcolemma as well as extracellular matrix, and the potential regulatory effects of endogenous inhibitors on protease activities are identified. Both extracellular and intracellular proteolytic activities appear to be imperative in determining the true extent of I/R injury and their inhibition seems to be of critical importance for improving the recovery of cardiac function. Thus, both extracellular and intracellular proteases may serve as potential targets for the development of cardioprotective interventions for reducing damage to the heart and retarding the development of contractile dysfunction caused by I/R injury.

Evidence of an intracellular angiotensin-generating system and non-AT1, non-AT2 binding site in a human pancreatic cell line

OBJECTIVES

To assess the presence of a local angiotensin-generating systems (LAGS) and its participation in tumor growth in the human pancreatic cancer derived cell line Capan-1.

METHODS

Capan-1 cells were cultured in Dulbecco modified Eagle medium, and angiotensin I was assayed by radioimmunoassay and angiotensin II and vascular endothelial growth factor were assayed by enzyme-linked immunosorbent assay in the supernatant. Immunohistochemistry and reverse transcription-polymerase chain reaction were performed for the expression of AT1 and AT2 receptors. Angiotensin II binding assays and blockade were studied.

RESULTS

High levels of both angiotensins I and II were found in Capan-1 cells, although neither angiotensin I nor angiotensin II was detected in the cell culture supernatant. Reverse transcription-polymerase chain reaction and immunocytochemistry revealed that Capan-1 cells do not express AT1 and AT2 receptors; however, specific binding to the cell membrane was identified for angiotensin II. Neither exogenous angiotensin II nor Dup753 (specific AT1 receptor blocker) affected Capan-1 cells' proliferation or vascular endothelial growth factor secretion.

CONCLUSIONS

Detection of both angiotensin I and angiotensin II along with specific binding of angiotensin II in Capan-1 cells provides evidence of the existence of a LAGS that operates in an intracrine manner. Intracellular angiotensin II may play a role in the aggressiveness of pancreatic cancer and is a possible target for therapeutic agents.

Kallikrein-kinin system: a surgical perspective in post-aprotinin era

Kallikrein-kinin system (KKS) plays an important role in inflammation, ischemia-reperfusion (IR) injury, and development of neoplasia. There is evidence to suggest that KKS plays an important role in organ protection during preconditioning. Aprotinin is a nonspecific serine protease inhibitor, which has been extensively used in cardiac surgery for the control of post operative bleeding. The anti-inflammatory effects of aproprotin are due to its inhibitory effect on the kallikrein-kinin system (KKS). We herein review KKS and its role as applied to the practice of surgery.

A Novel Category of Anti-Hypertensive Drugs for Treating Salt-Sensitive Hypertension on the Basis of a New Development Concept

Terrestrial animals must conserve water and NaCl to survive dry environments. The kidney reabsorbs 95% of the sodium filtered from the glomeruli before sodium reaches the distal connecting tubules. Excess sodium intake requires the renal kallikrein-kinin system for additional excretion. Renal kallikrein is secreted from the distal connecting tubule cells of the kidney, and its substrates, low molecular kininogen, from the principal cells of the cortical collecting ducts (CD). Formed kinins inhibit reabsorption of NaCl through bradykinin (BK)-B₂ receptors, localized along the CD. Degradation pathway of BK by kinin-destroying enzymes in urine differs completely from that in plasma, so that ACE inhibitors are ineffective. Urinary BK is destroyed mainly by a carboxypeptidase-Y-like exopeptidase (CPY) and partly by a neutral endopeptidase (NEP). Inhibitors of CPY and NEP, ebelactone B and poststatin, respectively, were found. Renal kallikrein secretion is accelerated by potassium and ATP-sensitive potassium (KATP) channel blockers, such as PNU-37883A. Ebelactone B prevents DOCA-salt hypertension in rats. Only high salt intake causes hypertension in animals deficient in BK-B2 receptors, tissue kallikrein, or kininogen. Hypertensive patients, and spontaneously hypertensive rats, excrete less kallikrein than normal subjects, irrespective of races, and become salt-sensitive. Ebelactone B, poststatin, and KATP channel blockers could become novel antihypertensive drugs by increase in urinary kinin levels. Roles of kinin in cardiovascular diseases were discussed.

Scorpion toxin of Androctonus australis garzonii induces neuropeptide Y release via bradykinin stimulation in rat atria and kidneys

The ability of scorpion toxins to produce hemodynamic alterations is well documented but all mediators implied in cardiovascular disturbances are not known. In the present investigation we studied the effect of North African Androctonus australis garzonii scorpion toxin on neuropeptide Y (NPY) release from rat atria and kidneys by a perifusion system in vitro. To further understand the mechanisms of the scorpion toxin action on NPY release, the effects of icatibant (HOE 140, a selective bradykinin-B2 receptor antagonist), tetrodotoxin (TTX, a sodium channel antagonist) and diltiazem (a calcium channel antagonist), and the effect of the scorpion toxin on bradykinin (BK, a potent vasorelaxant peptide of the kinin group) release were studied in both tissues. We showed that the scorpion toxin (10(-6)M) increased the NPY release from both atria (35%) and kidneys (40%). This increase was significantly (p<0.001) inhibited by HOE 140 (10(-5)M). The scorpion toxin (10(-6)M) enhanced BK secretion in both atria (52%) and kidneys (55%). Diltiazem (10(-5)M) and TTX (10(-5)M) decreased by 45-75% NPY levels induced by scorpion toxin in both organs. The results show that A. australis garzonii scorpion toxin stimulates NPY release from both rat atria and kidneys, and suggest that the toxin induces NPY release via BK stimulation through B2 receptors. This effect appears to involve calcium and sodium channel activation.

Protective actions of human tissue kallikrein gene in transgenic rat hearts

In this study, we used an experimental model of cardiac hypertrophy to explore the role of the kallikrein-kinin system (KKS) in cardiac protection in transgenic rats harboring the human tissue kallikrein gene, TGR(hKLK1). Tissue kallikrein cleaves low-molecular-weight kininogen to produce kinin peptides, which bind to kinin receptors and trigger a wide spectrum of biological effects. The transgene, under the control of the zinc-inducible metallothionein promoter, was expressed in most tissues including the heart, kidney, lung and brain. These animals were subjected to treatment with thyroid hormone in order to promote cardiac hypertrophy. Induction of cardiac hypertrophy revealed a marked protective effect caused by the expression of the kallikrein transgene, evidenced by the significantly reduced cardiac weight gain and the lower enhancement in the cardiac expression of atrial natriuretic peptide and collagen III, markers for hypertrophy and fibrosis, respectively. In conclusion, our data show that expression of tissue kallikrein exerts antihypertrophic and antifibrotic actions in the heart.

Characteristics of neural and humoral systems involved in the regulation of blood pressure in snakes

Cardiovascular function is affected by many mechanisms, including the autonomic system, the kallikrein-kinin system (KKS), the renin-angiotensin system (RAS) and the endothelin system. The function of these systems seems to be fairly well preserved throughout the vertebrate scale, but evolution required several adaptations. Snakes are particularly interesting for studies related to the cardiovascular function because of their elongated shape, their wide variation in size and length, and because they had to adapt to extremely different habitats and gravitational influences. To keep the normal cardiovascular control the snakes developed anatomical and functional adaptations and interesting structural peculiarities are found in their autonomic, KKS, RAS and endothelin systems. Our laboratory has characterized some biochemical, pharmacological and physiological properties of these systems in South American snakes. This review compares the components and function of these systems in snakes and other vertebrates, and focuses on differences found in snakes, related with receptor or ligand structure and/or function in autonomic system, RAS and KKS, absence of components in KKS and the intriguing identity between a venom and a plasma component in the endothelin system.

Functional characterization of the mechanisms underlying bradykinin-induced relaxation in the isolated rat carotid artery

This work aimed to functionally characterize the mechanisms underlying the relaxation induced by bradykinin (BK) in the rat carotid artery. Vascular reactivity experiments, using standard muscle bath procedures, showed that BK (0.1 nmol/L-3 mumol/L) induced relaxation of phenylephrine-pre-contracted rings in a concentration-dependent manner. Endothelial removal strongly attenuated BK-induced relaxation. HOE-140, the selective antagonist of bradykinin B(2) receptors concentration-dependently reduced the relaxation induced by BK. Pre-incubation of endothelium-intact rings with L-NAME (100 micromol/L), a non-selective nitric oxide synthase (NOS) inhibitor, L-NAME (100 micromol/L), a selective inhibitor of the eNOS or 7-nitroindazole (100 micromol/L), the selective inhibitor of nNOS, reduced BK-induced relaxation. Conversely, 1400 W (10 nmol/L), a selective inhibitor of iNOS, did not alter the relaxation induced by BK. Surprisingly, indomethacin (10 micromol/L) a non-selective inhibitor of cyclooxygenase (COX) increased BK-induced relaxation in endothelium-intact but not denuded rings. Neither SQ29548 (3 micromol/L), a competitive antagonist of PGH(2)/TXA(2) receptors nor AH6809 (10 micromol/L), an antagonist of PGF(2alpha) receptors significantly altered the relaxation induced by BK in endothelium-intact rings. The combination of SQ29548 and AH6809 increased BK-induced relaxation. The present study shows that the vasorelaxant action displayed by BK in the rat carotid is mediated by endothelial B(2) receptors and the activation of the NO pathway. The major finding of this work is that it demonstrated functionally that endothelial-derived vasoconstrictor prostanoids (probably PGH(2), TXA(2) and PGF(2alpha)) counteract the vasorelaxant action displayed by BK.

Vasopeptidase inhibition normalizes blood pressure and restores endothelial function in renovascular hypertension

BACKGROUND/AIMS

Vasopeptidase inhibitors by definition inhibit both angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP), therefore they may exceed the effect of ACE inhibitors in the treatment of hypertension. The present study investigated the effect of the vasopeptidase inhibitor AVE7688 in comparison to the ACE inhibitor ramipril on systolic blood pressure (SBP) and endothelial function in renovascular hypertension.

METHODS

Wistar-Kyoto rats with renovascular hypertension (two-kidney one-clamp-model) were randomized 2 weeks after unilateral clamping of the right renal artery for 3 weeks' oral treatment with either AVE7688 (30 mg/kg/day), ramipril (1 mg/kg/day) or placebo. SBP was measured by the tail-cuff method and endothelium-dependent and -independent vascular function was assessed in isolated preconstricted (norepinephrine 10(-7) mol/l) aortic rings as relaxation to acetylcholine (10(-10)-10(-4) mol/l) and sodium nitroprusside (10(-10)-10(-4) mol/l), respectively.

RESULTS

Two weeks after clamping, SBP was significantly elevated (196 +/- 16 vs. 145 +/- 8 mm Hg for sham-operated rats; p < 0.01) and further increased in placebo-treated animals to 208 +/- 19 mm Hg. Treatment with AVE7688 and ramipril had a similar blood pressure-lowering effect (119 +/- 8 and 124 +/- 10 mm Hg, respectively; p < 0.01 vs. placebo). Maximum endothelium-dependent relaxation was reduced in hypertensive rats (72 +/- 6 vs. 99 +/- 7% in control rats; p < 0.05). Endothelium-dependent relaxation was restored by AVE7688 (101 +/- 6%) and ramipril (94 +/- 8%), respectively, whereas endothelium-independent relaxation was comparable in all groups.

CONCLUSION

In renovascular hypertension the vasopeptidase inhibitor AVE7688 exhibited similar blood pressure-lowering and endothelial protective properties as compared to the ACE inhibitor ramipril. Therefore, in high renin models of hypertension, vasopeptidase inhibition may be considered an alternative treatment option to ACE inhibition.

Cross-talk of the renin-angiotensin and kallikrein-kinin systems

The renin-angiotensin (RAS) and kallikrein-kinin (KKS) systems play a key role in multiple physiological and pathophysiological conditions, including growth and development, inflammation, blood pressure regulation and control of renal function. In many instances, kinins and angiotensin II work together, e.g., during development, whereas they oppose each other's actions in the regulation of vascular tone and renal function. The RAS and KKS systems also interact at multiple levels, so that changes in the activity of one system greatly impact the activity of the other. The purpose of this brief review is to highlight recent knowledge regarding interactions at the cellular and molecular levels between the two systems, with an emphasis on the coordinate developmental regulation of these phylogenetically conserved vasoactive systems.

Role of tissue kallikrein-kininogen-kinin pathways in the cardiovascular system

All the components of the kallikrein-kinin system are located in the cardiac muscle, and its deficiency may lead to cardiac dysfunction. In recent years, numerous observations obtained from clinical and experimental models of diabetes, hypertension, cardiac failure, ischemia, myocardial infarction and left ventricular hypertrophy have suggested that the reduced activity of the local kallikrein-kinin system may be instrumental for the induction of cardiovascular-related diseases. The cardioprotective property of the angiotensin converting enzyme inhibitors is primarily mediated via kinin-releasing pathway, which may cause regression of the left ventricular hypertrophy in hypertensive situations. The ability of kallikrein gene delivery to produce a wide spectrum of beneficial effects makes it an excellent candidate in treating hypertension, cardiovascular and renal diseases. In addition, stable kinin agonists may also be available in the future as therapeutic agents for cardiovascular and renal disorders.

Modulation of renal kallikrein by a high potassium diet in rats with intense proteinuria

Injury of the renal tubulointerstitial compartment is recognized to play an important role in hypertension. Its damage may in turn, impair the activity of vasodepressor systems, like the kallikrein-kinin, in blood pressure regulation. The overload proteinuria model induces tubulointerstitial injury with activation of the renin-angiotensin system, but renal kallikrein and the development of hypertension have not received special attention. Sprague-Dawley rats received seven intraperitoneal doses of bovine serum albumin (BSA) 2 g/day under normosodic diet and were hydrated ad libitum. A second group received a high potassium diet to stimulate kallikrein production during the previous four weeks and while under BSA administration. A third one received potassium and BSA in the same schedule, but with the kinin B2 receptor antagonist, HOE140, added during the protein load phase. A control group received seven saline injections. Kallikrein protein was detected by immune labeling on renal sections and enzymatic activity in the urine. The BSA group showed massive proteinuria followed by intense tubulointerstitial damage. Blood pressure increased after the third dose in BSA animals, remaining elevated throughout the experiment, associated with significant reductions in renal expression and urinary activity of kallikrein, compared with controls. An inverse correlation was found between blood pressure and immunohistochemistry and urinary activity of kallikrein. Potassium induced a significant increase in both urinary activity and renal kallikrein expression, associated with significant reduction in blood pressure. The HOE140 antagonist blunted the antihypertensive effect of kallikrein stimulation in proteinuric rats. Loss of renal kallikrein, produced by tubulointerstitial injury, may participate in the pathogenesis of the hypertension observed in this model.

Aprotinin suppresses ACE-inhibitor cough triggered by TAME-esterase

N-alpha-Tosyl l-arginine methyl ester [TAME]-esterase appears to be an important biochemical marker, which displays potent contractile properties on bronchial tissues and aorta in vitro. TAME-esterase induced contractions have been shown to be mediated via a nitric oxide-cyclic GMP pathway. TAME-esterase has also been described to be a possible new cardiovascular risk factor among smokers. TAME-esterase has been reported to be an enzyme, which is involved during the sequence of events leading to the activation of the kinin-kallikrein system. Use of aprotinin (a kallikrein inhibitor) as well as aspirin and indomethacin (prostaglandin inhibitors) have shown that there is an inter-dependent relationship between the kinin-kallikrein system and the cyclo-oxygenase pathway involved during the sequence of reactions leading to TAME-esterase induced contractions. Our findings also lend support to the concept of calcium antagonism whereby verapamil, and nifedipine, mimicked in reversible fashion the effects of Ca2+ withdrawal on muscle excitability during TAME-esterase induced contractions on rat aorta in vitro. We concluded that the effects of captopril, an ACE inhibitor, on TAME-esterase induced contractions could thus be due to the degradation of bradykinin by the enzyme kininase being blocked. This paper proposes an integrated model of possible biochemical-pharmacological pathways, which involve events leading to TAME-esterase induced contractions. We hypothesize that TAME-esterase induced cough through sensitization of airway sensor nerves in hypertensive patients taking angiotensin-converting enzyme inhibitors can be inhibited by aprotinin.

Does the kinin system mediate in cardiovascular abnormalities? An overview

All the components of the kallikrein-kinin system are located in the cardiac muscle, and its deficiency may lead to cardiac dysfunction. In recent years, numerous observations obtained from clinical and experimental models of diabetes, hypertension, cardiac failure, ischemia, myocardial infarction, and left ventricular hypertrophy have suggested that the reduced activity of the local kallikrein-kinin system may be instrumental for the induction of cardiovascular-related diseases. The cardioprotective property of the angiotensin-converting enzyme inhibitors is primarily mediated via the kinin-releasing pathway, which may cause regression of left ventricular hypertrophy in hypertensive situations. The ability of kallikrein gene delivery to produce a wide spectrum of beneficial effects makes it an excellent candidate in treating hypertension and cardiovascular and renal diseases. In addition, stable kinin agonists may also be available in the future as therapeutic agents for cardiovascular and renal disorders.

Effects of aspirin on N-alpha-tosyl L-arginine methyl ester [TAME]-esterase induced contractions on rat aorta in vitro

The present study was designed to investigate whether N-alpha-tosyl L-arginine methyl ester [TAME]-esterase activation could be the result of endothelial dysfunction. Thoracic aorta from rats was mounted in an organ bath containing Krebs solution. Intact and endothelium denuded aortic strips were challenged with different concentrations of TAME (10(-15)-10(-1) m). The effects of aspirin, a cyclo-oxygenase pathway inhibitor, were also studied on [TAME]-esterase induced contraction on rat aorta strips. Our results showed that aspirin definitely blocked TAME-esterase induced contractions on rat aortic strips. In conclusion, the present work supported the hypothesis that [TAME]-esterase induced contraction in rat aorta in vitro was mediated through release of prostaglandin(s) as a result of endothelial dysfunction.

The renal kallikrein-kinin system: its role as a safety valve for excess sodium intake, and its attenuation as a possible etiologic factor in salt-sensitive hypertension

The distal tubules of the kidney express the full set of the components of the kallikrein-kinin system, which works independently from the plasma kallikrein-kinin system. Studies on the role of the renal kallikrein-kinin system, using congenitally kininogen-deficient Brown-Norway Katholiek rats and also bradykinin B2 receptor knockout mice, revealed that this system starts to function and to induce natriuresis and diuresis when sodium accumulates in the body as a result of excess sodium intake or aldosterone release, for example, by angiotensin II. Thus, it can be hypothesized that the system works as a safety valve for sodium accumulation. The large numbers of studies on hypertensive animal models and on essential hypertensive patients, particularly those with salt sensitivity, indicate a tendency toward the reduced excretion of urinary kallikrein, although this reduction is modified by potassium intake and impaired renal function. We hypothesize that the reduced excretion of the renal kallikrein may be attributable to a genetic defect of factor(s) in renal kallikrein secretion process and may cause salt-sensitive hypertension after salt intake.

Sevoflurane and bradykinin-induced calcium mobilization in pulmonary arterial valvular endothelial cells in situ: sevoflurane stimulates plasmalemmal calcium influx into endothelial cells

Kinins locally synthesized in the cardiovascular tissue are believed to contribute to the regulation of cardiovascular homeostasis by stimulating the endothelial cells to release nitric oxide, prostacyclin, or a hyperpolarizing factor via autocrine-paracrine mechanisms. This study was designed to investigate the action of sevoflurane on bradykinin-induced Ca2+ mobilization in endothelial cells in situ. Utilizing fura-2-loaded rat pulmonary arterial valve leaflets, the effects of sevoflurane were examined on bradykinin-induced increases in intracellular Ca2+ concentration ([Ca2+]i) in endothelial cells in situ. In the presence of extracellular Ca2+ (1.5 mM), bradykinin (3-30 microM) produced an initial phasic and a subsequent tonic increase in [Ca2+]i in a concentration-dependent manner. However, it produced only the phasic increase in [Ca2+]i in the absence of extracellular Ca2+. Sevoflurane (5%, 0.67 mM) inhibited both the phasic and tonic responses to bradykinin. In these experiments, sevoflurane (3-5%) generated sustained increases (approximately 20-40% of the bradykinin-induced maximal increase in [Ca2+]i) in the resting [Ca2+]i level. Sevoflurane still increased [Ca2+]i after depletion of the intracellular Ca stores with ionomycin (0.1 microM ). However, the sevoflurane-induced increase in [Ca2+]i was eliminated by removal of the extracellular Ca and attenuated by NiCl (1-3 mM). In conclusion, in the pulmonary arterial valvular endothelial cells, sevoflurane inhibits both bradykinin-induced Ca2+ release from the intracellular stores and bradykinin-induced plasmalemmal Ca2+ influx. In addition, sevoflurane appears to stimulate the plasmalemmal Ca2+ influx and thereby increase the endothelial [Ca2+]i level. Sevoflurane might influence the pulmonary vascular tone through its direct action on the pulmonary arterial valvular endothelial cells.

Contraction-related factors affect the concentration of a kallidin-like peptide in rat muscle tissue

In order to study the effects of the manipulation of various factors related to muscular activity on the concentration of kinins in muscular tissue, a microdialysis probe was implanted in the adductor muscle of the hindlimb in anaesthetized rats. After collection of baseline samples, the perfusion fluid was changed to a Ringer solution containing sodium lactate (10 or 20 mM), adenosine (50 or 100 microM) or a lower pH (7.0 or 6.6). Whereas perfusion with lactate did not have any significant effect on the concentration of kinins in the dialysate, the perfusion with a lower pH or with adenosine dose-dependently increased the kinin content in the samples. In a second microdialysis experiment, by using specific radioimmunoassays (RIA) for bradykinin and kallidin, we observed that about 70 % of the total kinins dialysed from rat muscle are a kallidin-like peptide. Also, the simultaneous perfusion with 100 microM caffeine totally abolished the increase in kinin levels induced by the perfusion at pH 6.6. In a third experiment, soleus muscles from rat were stimulated in vitro during 30 min in the presence or absence of 77 microM caffeine. Electrically stimulated contraction, but not the addition of 10 mU ml(-1) insulin, induced an increase in the concentration of the kallidin-like peptide in the buffer. This effect was totally prevented by the addition of the adenosine antagonist caffeine. These results show that a kallidin-like peptide is released from rat muscle, and that its production is enhanced by muscle activity. Furthermore, the increase in kinin peptides during muscle contraction may be mediated by an increase in adenosine levels.

The mechanism of the angiotensin-converting enzyme inhibitor quinapril is not related to bradykinin level in heart tissue

In order to examine the effect of the angiotensin-converting enzyme inhibitor (ACEi) quinapril, we performed a sensitive and specific radioimmunoassay (RIA) to quantify bradykinin, BK-(1-9), in heart and kidney tissues. The BK-(1-9) level was unaffected in the heart of sham and water-deprived rats treated for 2h with quinapril (10mg/kg), but was significantly higher in the kidneys in the two groups. In these conditions, circulating and tissue angiotensin II (Ang II) levels were significantly decreased by quinapril. Moreover, our results indicated that acute treatment with this dose of quinapril induced kinin-mediated effects which were not related to its action on bradykinin degradation in rat hearts.

Multiple interactions between the renin-angiotensin and the kallikrein-kinin systems: role of ACE inhibition and AT1 receptor blockade

The investigation of therapeutic actions of angiotensin type 1 (AT1) receptor antagonists and ACE inhibitors (ACEI) demonstrated complex interactions between the renin-angiotensin system (RAS) and the kallikrein-kinin system (KKS) in several experimental and clinical studies. They are evidenced by the fact that (1) ACE efficiently catabolizes kinins; (2) angiotensin-derivatives such as ANG-(1-7) exert kininlike effects; and (3) kallikrein probably serves as a prorenin-activating enzyme. (4) Several authors have demonstrated experimentally that the protective effects of ACEI are at least partly mediated by a direct potentiation of kinin receptor response on BK stimulation. (5) Furthermore, studies on AT1 antagonists, which do not directly influence kinin degradation, and studies on angiotensin-receptor transgenic mice have revealed additional interactions between the RAS and the KKS. There is mounting evidence that an autocrine cascade including kinins, nitric oxide, prostaglandins, and cyclic GMP is involved in at least some of the angiotensin type 2 receptor effects. This review discusses multiple possibilities of cross-talks between the RAS and KKS in vascular and cardiac physiology and pathology after ACE inhibition and AT1 receptor blockade.

Vasopeptidase inhibition: effective blood pressure control for vascular protection

Angiotensin converting enzyme (ACE) inhibition is a well-established principle in the treatment of hypertension, and numerous large scale clinical studies have clearly demonstrated the beneficial effects of inhibiting the renin-angiotensin-aldosterone system (RAS) in hypertension. The clinical success of ACE inhibitors encouraged attempts to inhibit other key enzymes in the regulation of vascular tone, such as the neutral endopeptidase (NEP). Similar to ACE, NEP is an endothelial cell surface metalloproteinase, which is involved in the degradation of several regulatory peptides including the natriuretic peptides, and augments vasodilatation and natriuresis through increased levels of atrial natriuretic peptide. By inhibiting the RAS and potentiating the natriuretic peptide system at the same time, combined NEP/ACE inhibitors, the so-called "vasopeptidase inhibitors," reduce vasoconstriction and enhance vasodilatation, and in turn decrease peripheral vascular resistance and blood pressure. Within the vessel wall this may lead to a reduction of vasoconstrictor and proliferative mediators such as angiotensin II and endothelin-1, and may increase local levels of bradykinin as well as natriuretic peptides. Based on these considerations, numerous preclinical studies with vasopeptidase inhibitors have been performed and reveal promising results in experimental hypertension. Correspondingly, large-scale clinical studies in patients with hypertension are on the way, to transfer the principle of vasopeptidase inhibition from bench to bedside.

Cardiovascular properties of the kallikrein-kinin system

All the components of the kallikrein-kinin system are located in the vascular smooth muscle as well as in the heart. In recent years, numerous observations obtained from clinical and experimental models of diabetes, hypertension, cardiac failure, ischaemia, myocardial infarction and left ventricular hypertrophy, have suggested that the reduced activity of the local kallikrein-kinin system may be instrumental in the induction of cardiovascular-related diseases. The ability of kallikrein gene delivery to produce a wide spectrum of beneficial effects makes it an excellent candidate in treating hypertension, and cardiovascular and renal diseases. In addition, stable kinin agonists may also be available in the future as therapeutic agents for cardiovascular and renal disorders.

Amlodipine enhances NO production induced by an ACE inhibitor through a kinin-mediated mechanism in canine coronary microvessels

Our previous study found that angiotensin-converting enzyme (ACE) inhibitors and amlodipine induce NO release from coronary microvessels through a kinin-dependent mechanism. The goal of this study was to determine whether amlodipine could potentiate NO formation during ACE inhibition. Coronary microvessels were isolated from 16 mongrel dogs. Nitrite, the hydration product of NO, from coronary microvessels was quantified by using the Griess reaction. Bradykinin and kallikrein all significantly increased nitrite release from coronary microvessels in a concentration-dependent manner. The ACE inhibitor, ramiprilat, potentiated these effects. Amlodipine also markedly potentiated nitrite production by ramiprilat. For instance, amlodipine (10(-10) M) enhanced nitrite release induced by ramiprilat (10(-7) M) from 122 +/- 9 to 168 +/- 14 pmol/mg (p < 0.05 vs. ramiprilat). Nitrite release potentiated by ramiprilat and amlodipine was entirely blocked by N(omega)-nitro-L-arginine methyl ester (L-NAME, an inhibitor of NO synthase), HOE 140 (Icatibant, a specific B2-kinin receptor antagonist), and dichloroisocoumarin (DCIC, a serine protease inhibitor that blocks local kinin formation). These results clearly show that there is a synergistic effect on NO formation when amlodipine is combined with ACE inhibition. Our data suggest that kinin-mediated coronary NO production may contribute importantly to the beneficial therapeutic action of ACE inhibitors, especially in combination with amlodipine in the treatment of heart disease.

Promoter polymorphism of the beta2 bradykinin receptor gene is associated with essential hypertension

The present study examined the genetic contribution of the human beta2 bradykinin receptor gene in Japanese subjects with essential hypertension, and identified a -58T/C polymorphism of the core promoter that might be responsible for essential hypertension in Japanese. The study consisted of 100 hypertensive subjects and 100 age- and sex-matched controls. The allelic frequencies were 0.575 for the C allele and 0.425 for the T allele in hypertensive subjects, and 0.465 for the C allele and 0.535 for the T allele in normotensive subjects. The allelic frequencies were in Hardy-Weinberg equilibrium. Significant differences between hypertensive and normotensive subjects were seen in the genotypes distribution (p=0.049) and allelic frequencies (p=0.028), and the beta2 bradykinin receptor gene variant was associated with human essential hypertension in this Japanese population. This new marker may provide a valuable tool for assessing the risk for putative bradykinin-associated common diseases, such as hypertension, and cardiovascular diseases with genetic determinism. These results suggest that the -58 polymorphism of the human beta2 bradykinin receptor gene is an independent risk factor for essential hypertension in the Japanese population.

Effects of aminopeptidase P inhibition on kinin-mediated vasodepressor responses

We studied in anesthetized rats whether aminopeptidase P (AMP) may be involved in bradykinin (BK) metabolism and responses. For this we inhibited AMP with the specific inhibitor apstatin (Aps). Studies were done with Aps alone or together with the angiotensin-converting enzyme inhibitor lisinopril (Lis). Aps increased the vasodepressor response to an intravenous bolus of BK (400 ng/kg): vehicle, -3.0 +/- 0.7 mmHg; Aps, -7.8 +/- 0.7 mmHg (P < 0.01 vs. vehicle); Lis, -23.8 +/- 1.8 mmHg; Aps + Lis, -37.5 +/- 1.9 mmHg (P < 0.01 vs. Lis). Aps did not affect the vasodepressor response to BK given into the descending aorta. Plasma BK increased only in Aps + Lis-treated rats (in pg/ml): control, 48.0 +/- 1.4; Lis, 57.5 +/- 7.6; Aps + Lis, 121. 8 +/- 30.6 (P < 0.05 vs. control or Lis), whereas in rats infused with BK (400 ng. kg-1. min-1 for 5 min), Aps increased plasma BK (in pg/ml): control, 51.9 +/- 2.5; Aps, 83.5 +/- 20.5; Lis, 725 +/- 225; Aps + Lis, 1,668 +/- 318 (P < 0.05, Aps vs. control and Lis vs. Aps + Lis). In rats with aortic coarctation hypertension, the acute antihypertensive effects of Aps plus Lis were greater than Lis alone (P < 0.01). Hoe-140, a BK B2-receptor antagonist, abolished the difference. We concluded that in the rat AMP contributes to regulation of BK metabolism and responses.

Bradykinin and its receptors in non-mammalian vertebrates

The generation of bradykinin (BK) in blood by the action of the kallikrein-kinin system has been studied intensively in mammals but the system has received relatively little attention in non-mammalian vertebrates. The plasma of crocodilians and Testudines (turtles and tortoises) contains all the components of the kallikrein-kinin system found in mammals (prekallikrein activator, prekallikrein, kininogen, and kininases) and activation results in generation of [Thr6]-BK. Plasma of birds and snakes probably lacks a prekallikrein activator analogous to mammalian Factor XII but treatment with exogenous proteases (pig pancreatic kallikrein and/or trypsin) generates [Thr6, Leu8]-BK (chicken), [Ala1, Thr6]-BK (python) and [Val1, Thr6]-BK (colubrid snakes). The skins of certain frogs, particularly of the genus Rana, contain very high concentrations of BK-related peptides but their pathway of biosynthesis involves the action of cellular endoproteinase(s) cleaving at the site of single arginyl residues rather than by the action of the kallikrein-kinin system. Evidence for a prekallikrein activator in fish plasma is lacking but treatment with exogenous proteases generates [Arg0, Trp5, Leu8]-BK (trout and cod), [Trp5]-BK (bowfin and gar), [Met1, Met5]-BK (sturgeon). The cardiovascular actions and effects upon gastrointestinal smooth muscle of these peptides in their species of origin differ markedly. For example, intra-arterial injections of the native BK peptides into unanesthetized fish produce transient hypertension in the cod, complex depressor and pressor responses in the trout and bowfin and hypotension in the sturgeon. Pharmacological studies in snakes and fish and with the recombinantally expressed chicken BK receptor have demonstrated that the BK receptors in the tissues of non-mammalian vertebrates have appreciably different ligand binding properties from the well-characterized mammalian B1 and B2 receptors.

Angiotensin-Converting Enzyme Inhibitors an Angiotensin II-Receptor Antagonists

The renin-angiotensin-aldosterone system (RAAS) is one of the main targets in the pharmacotherapy of cardiovascular diseases. Inhibitors of the angiotensin- converting enzyme (ACE) have been in clinical use for years and a great deal of experience exists with this particular group of drugs. However, the therapeutic effect is based on the inhibition of an enzyme (ACE) that is not very specific. Another substrate is bradykinin, a well-known mediator of inflammation and a potent inductor of vasodilatation and bronchoconstriction. Dur ing therapy with an ACE inhibitor, the inactivation of bradykinin by cleavage of the carboxyterminal end of this nonpeptide is blocked as well, with the result of bradykinin accumulation. The pattern of adverse effects seen with ACE inhibitors is mainly determined by bradykinin-mediated actions such as edema and cough. Therefore, the inhibition of the RAAS at the level of the transmitter-receptor interaction seems to be a logical development. Because nonpeptide (ie, orally active) angiotensin II (AT) receptor antagonists are available, this concept can be proven.

Evidence for the presence of a kininogen-like species in a case of total deficiency of low and high molecular weight kininogens

Low and high molecular weight kininogens (LK and HK), containing 409 and 626 amino acids with masses of approximately 65 and 120 kDa after glycosylation, respectively, are coded by a single gene mapped to the human chromosome 3 by alternative splicing of the transcribed mRNA. The NH2-termini Glu1-Thr383 region, identical in LK and HK, contains bradykinin (BK) moieties Arg363-Arg371. LK, HK and their kinin products Lys-BK and BK are involved in several biologic processes. They are evolutionarily conserved and only 7 patients, all apparently normal, have been reported to lack them. In one of these patients (Williams' trait), a codon mutation (Arg178-->stop) has been blamed for the absence of LK and HK. However, using Western blots with 2 monoclonal anti-HK antibodies, one that recognizes the region common to LK and HK and the other that recognizes only HK, 1 detected approximately 110-kDa bands in the plasma of this LK/HK-deficient patient vs approximately 120-kDa bands in normal human and ape plasmas. With polyclonal anti-Lys-BK antibody, which strongly detects BK cleaved at its COOH-terminus in purified HK, 1 detected approximately 110-kDa bands in the normal and the deficient plasmas. Western blots with a monoclonal anti-prekallikrein (PK) antibody showed that surface activation of PK and distribution of PK activation products, both dependent on HK, were similar in these plasmas. These findings suggest that a mutant gene yielded a kininogen-like species possibly involving aberrant mRNA splicing-structurally different from normal HK, but apparently with the capacity to carry out seemingly vital HK functions.

Left ventricular hypertrophy and its relation to the cardiac kinin-forming system in hypertensive and diabetic rats

We investigated the cardiac tissue kallikrein and kininogen levels, left ventricular wall thickness and mean arterial blood pressure of Wistar Kyoto and spontaneously hypertensive rats with and without streptozotocin-induced diabetes. The mean arterial blood pressure was highly elevated (P<0.001) in Wistar Kyoto diabetic and spontaneously hypertensive diabetic rats as compared with their respective controls. The cardiac tissue kallikrein and kininogen levels were reduced significantly (P<0.001) in diabetic Wistar Kyoto, spontaneously hypertensive and diabetic spontaneously hypertensive compared with Wistar Kyoto control rats. In addition, the left ventricular thickness was found to be increased (P<0.001) in diabetic Wistar Kyoto and spontaneously hypertensive rats in the presence and in the absence of diabetes. Our results indicate that reduced activity of the kinin-forming system may be responsible for inducing left ventricular hypertrophy in the presence of raised mean arterial blood pressure in diabetic and hypertensive rats. Thus, the kinin-forming components might have a protective role against the development of left ventricular hypertrophy. The possible significance of these findings is discussed.

Bradykinin B2-receptor activation augments norepinephrine exocytosis from cardiac sympathetic nerve endings. Mediation by autocrine/paracrine mechanisms

We determined whether local bradykinin production modulates cardiac adrenergic activity. Depolarization of guinea pig heart sympathetic nerve endings (synaptosomes) with 1 to 100 mmol/L K+ caused the release of endogenous norepinephrine (10% to 50% above basal level). This release was exocytotic, because it depended on extracellular Ca2+, was inhibited by the N-type Ca(2+)-channel blocker omega-conotoxin and the protein kinase C inhibitor Ro31-8220, and was potentiated by the neuronal uptake-1 inhibitor desipramine. Typical of adrenergic terminals, norepinephrine exocytosis was enhanced by activation of prejunctional angiotensin AT1-receptors and attenuated by adrenergic alpha 2-receptors, adenosine A1-receptors, and histamine H3-receptors. Exogenous bradykinin enhanced norepinephrine exocytosis by 7% to 35% (EC50, 17 nmol/L), without inhibiting uptake 1. B2-receptor, but not B1-receptor, blockade antagonized this effect. The kininase II/angiotensin-converting enzyme inhibitor enalaprilat and the addition of kininogen or kallikrein enhanced norepinephrine exocytosis by approximately equal to 6% to 40% (EC50, 20 nmol/L) and approximately equal to 25% to 60%, respectively. This potentiation was prevented by serine protease inhibitors and was antagonized by B2-receptor blockade. Therefore, norepinephrine exocytosis is augmented when bradykinin synthesis is increased or when its breakdown is inhibited. This is the first report of a local kallikrein-kinin system in adrenergic nerve endings capable of generating enough bradykinin to activate B2-receptors in an autocrine/paracrine fashion and thus enhance norepinephrine exocytosis. This amplification process may operate in disease states, such as myocardial ischemia, associated with severalfold increases in local kinin concentrations.

Beneficial effects of bradykinin on myocardial energy metabolism and infarct size

There is growing evidence for a local kallikrein-kinin system in the heart. In the ischemic heart the enhanced generation and release of kinins seem to have cardioprotective actions. In isolated rat hearts with ischemia-reperfusion injuries, perfusion with bradykinin reduces the duration and incidence of ventricular fibrillations, improves cardiodynamics, reduces release of cytosolic enzymes, and preserves energy-rich phosphates and glycogen stores. In anesthetized animals, intracoronary infusion of bradykinin is followed by comparable beneficial changes and limits infarct size. Inhibition of breakdown of bradykinin and related peptides induces similar beneficial cardiac effects. Treatment with angiotensin-converting enzyme (ACE) inhibitors such as ramipril increases cardiac kinins and reduces postischemic reperfusion injuries in isolated rat hearts as well as infarct size and remodeling in postinfarcted animals, respectively. Blockade of B2 kinin receptors increases ischemia-induced effects. In isolated hearts, ischemia-reperfusion injuries intensify with the B2 kinin receptor antagonist icatibant, which also abolishes the cardioprotective effects of ACE inhibitors and of exogenous bradykinin. Infarct size reduction by ACE inhibitors and bradykinin in anesthetized animals is reversed by icatibant. Kinins contribute to the cardioprotective effects associated with ischemic preconditioning. Preconditioning or bradykinin-induced antiarrhythmic and infarct size-limiting effects are attenuated by icatibant.

Effect of bradykinin B2-receptor antagonism on post-ischemic coronary reperfusion

Isolated rabbit hearts in a modified Langendorff preparation were used to study the role of bradykinin B2-receptor antagonism on recovery from cardiac ischemia. The experiments were performed to clarify a potential risk of administrating BK-receptor antagonists in patients with coronary heart disease and patients undergoing heart surgery. The hearts were perfused in an open system at a constant pressure of 70 mm Hg and at a constant temperature of 37 degrees C with Krebs-Henseleit-buffer solution containing 6.5% HAES (hydroxyethyl-amylopectin) and 10 mmol Na-pyruvate/l. The perfusate was equilibrated to a PO2 of about 500-600 mm Hg. After a steady state period of 30 min, coronary perfusion was stopped for 30 min and the hearts were subsequently reperfused for further 30 min. Pretreatment with the B2-receptor antagonist, CP-0127, significantly increased (p < 0.001) the coronary vascular resistance during reperfusion from 31.9 +/- 2.1 to 59.0 +/- 6.5 mm Hg/ml/min/10 g wt and decreased the left ventricular pressure amplitude to 44.0 +/- 15.2% (p < 0.005) of it's baseline. When ischemia was combined with hyperkalaemic cardioplegia, CP-0127 did not influence coronary vascular resistance, but depressed, only to a minor degree, left ventricular pressure amplitude to 65.1 +/- 15.4% (p < 0.005) during reperfusion. Arrhythmias during reperfusion with cardiac arrest occurred only in 2 hearts with B2-receptor inhibition when ischemia was not combined with cardioplegia. Dependent on the initial functional status of the heart B2-receptor inhibition impaired recovery from acute coronary ischemia by increasing the coronary vascular resistance and depressing the myocardial function and therefore may constitute a risk in patients undergoing heart surgery and extracorporeal circulation.