Modulatory effect of bradykinin on noradrenaline release in isolated atria from normal and B2 knockout transgenic mice

Role of Kinins in Hypertension and Heart Failure

The kallikrein-kinin system (KKS) is proposed to act as a counter regulatory system against the vasopressor hormonal systems such as the renin-angiotensin system (RAS), aldosterone, and catecholamines. Evidence exists that supports the idea that the KKS is not only critical to blood pressure but may also oppose target organ damage. Kinins are generated from kininogens by tissue and plasma kallikreins. The putative role of kinins in the pathogenesis of hypertension is discussed based on human mutation cases on the KKS or rats with spontaneous mutation in the kininogen gene sequence and mouse models in which the gene expressing only one of the components of the KKS has been deleted or over-expressed. Some of the effects of kinins are mediated via activation of the B2 and/or B1 receptor and downstream signaling such as eicosanoids, nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF) and/or tissue plasminogen activator (T-PA). The role of kinins in blood pressure regulation at normal or under hypertension conditions remains debatable due to contradictory reports from various laboratories. Nevertheless, published reports are consistent on the protective and mediating roles of kinins against ischemia and cardiac preconditioning; reports also demonstrate the roles of kinins in the cardiovascular protective effects of the angiotensin-converting enzyme (ACE) and angiotensin type 1 receptor blockers (ARBs).

β-blockade abolishes the augmented cardiac tPA release induced by transactivation of heterodimerised bradykinin receptor-2 and β2-adrenergic receptor in vivo

Bradykinin (BK) receptor-2 (B2R) and β2-adrenergic receptor (β2AR) have been shown to form heterodimers in vitro. However, in vivo proofs of the functional effects of B2R-β2AR heterodimerisation are missing. Both BK and adrenergic stimulation are known inducers of tPA release. Our goal was to demonstrate the existence of B2R-β2AR heterodimerisation in myocardium and to define its functional effect on cardiac release of tPA in vivo. We further investigated the effects of a non-selective β-blocker on this receptor interplay. To investigate functional effects of B2R-β2AR heterodimerisation (i. e. BK transactivation of β2AR) in vivo, we induced serial electrical stimulation of cardiac sympathetic nerves (SS) in normal pigs that underwent concomitant BK infusion. Both SS and BK alone induced increases in cardiac tPA release. Importantly, despite B2R desensitisation, simultaneous BK infusion and SS (BK+SS) was characterised by 2.3 ± 0.3-fold enhanced tPA release compared to SS alone. When β-blockade (propranolol) was introduced prior to BK+SS, tPA release was inhibited. A persistent B2R-β2AR heterodimer was confirmed in BK-stimulated and non-stimulated left ventricular myocardium by immunoprecipitation studies and under non-reducing gel conditions. All together, these results strongly suggest BK transactivation of β2AR leading to enhanced β2AR-mediated release of tPA. Importantly, non-selective β-blockade inhibits both SS-induced release of tPA and the functional effects of B2R-β2AR heterodimerisation in vivo, which may have important clinical implications.

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.

Potentiation of nicotinic currents by bradykinin in the paratracheal ganglia neurons of rats

The effects of bradykinin on nicotine-induced responses were investigated in neurons dissociated from rat paratracheal ganglia using the nystatin-perforated patch-clamp recording technique. When bradykinin (10(-9) to 10(-8) M) was pretreated and then simultaneously applied with 10(-5) M nicotine, bradykinin potentiated the nicotine-induced currents. The potentiation was mimicked by [Hyp3]-bradykinin and inhibited by HOE-140, pertussis toxin, neomycin and U-73122, but not U-73433. These results suggest that bradykinin potentiates nicotinic currents via bradykinin B2 receptor, pertussis toxin-sensitive G-protein and phospholipase C. Since bradykinin inhibits the M-current via bradykinin B2 receptor and pertussis toxin-insensitive G-protein [Mochidome, T., Ishibashi, H., Takahama, K., 2001. Bradykinin activates airway parasympathetic ganglion neurons by inhibiting M-currents. Neuroscience 105, 785-791.], it seemed that bradykinin B2 receptor activated two distinct signal transduction pathways in the paratracheal ganglia neurons. This effect of bradykinin might cause enhanced synaptic transmission in paratracheal ganglia neurons and contribute to the aggravation of pathological conditions of the lower airway via enhanced acetylcholine release from the postganglionic nerve terminals.

Lack of CB1 receptors increases noradrenaline release in vas deferens without affecting atrial noradrenaline release or cortical acetylcholine release

1. We studied whether cannabinoid CB1 receptor gene disruption (to yield CB1-/- mice) affects the electrically evoked tritium overflow from vas deferens and atrial pieces preincubated with [3H]-noradrenaline (NA) ('noradrenaline release') and from cerebral cortex slices preincubated with [3H]-choline ('acetylcholine release'). 2. NA release was higher by 37% in vas deferens from CB1-/- mice than in vas deferens from CB1+/+ mice. The cannabinoid receptor agonist WIN 55,212-2 inhibited, and the CB1 receptor inverse agonist/antagonist SR 141716, increased NA release in vas deferens from CB1+/+ mice without affecting it in vas deferens from CB1-/- mice. 3. Atrial NA release did not differ between CB1+/+ and CB1-/- mice nor did WIN 55,212-2 affect NA release in either strain. 4. Cortical acetylcholine (Ach) release did not differ between CB1+/+ and CB1-/- mice. WIN 55,212-2 inhibited, but SR 141716 did not affect, Ach release in the cortex from CB1+/+ mice. Both drugs did not alter Ach release in the cortex from CB1-/- mice. 5. Tritium content did not differ between CB1+/+ and CB1-/- mice in any preparation. 6. In conclusion, the increase in NA release associated with CB1 receptor deficiency in the vas deferens, which cannot be ascribed to an alteration of tritium content of the preparations, suggests an endogenous tone at the CB1 receptors of CB1+/+ mice in this tissue. Furthermore, the effect of WIN 55,212-2 on NA release in the vas deferens and on cortical Ach release involves CB1 receptors, whereas the involvement of non-CB1-non-CB2 receptors can be excluded.

Bradykinin enhances sympathetic neurotransmission in rat blood vessels

Bradykinin evokes endothelium-dependent relaxation in some vascular beds; on the other hand, the possibility has been demonstrated that in certain organs, such as the adrenal medulla or atria, bradykinin may enhance transmitter release from the sympathetic nerves. We hypothesized that bradykinin may also enhance postganglionic sympathetic neurotransmission in blood vessels. To test this hypothesis, we recorded excitatory junction potentials (EJPs), a measure of sympathetic purinergic neurotransmission, in rat mesenteric resistance arteries with a conventional microelectrode technique. EJPs were elicited by repetitive perivascular nerve stimulation (1 Hz, 20 to 50 V, 30 to 60 micros, 11 pulses). In this preparation, bradykinin (10(-7) or 10(-6) mol/L) significantly enhanced the amplitude of EJPs without altering the resting membrane potential. This effect of bradykinin was blocked by Hoe 140, a bradykinin B2 receptor antagonist, but not by des-Arg(9),[Leu(8)]-bradykinin, a bradykinin B1 receptor antagonist. The cyclooxygenase inhibitor indomethacin or NO synthase inhibitor N(G)-nitro-L-arginine did not alter the effect of bradykinin. Captopril, an ACE inhibitor, but not candesartan, an angiotensin II type 1 receptor antagonist, enhanced the action of a low concentration (10(-8) mol/L) of bradykinin on EJPs. These findings suggest that in rat mesenteric resistance arteries, bradykinin enhances sympathetic purinergic neurotransmission, presumably through presynaptic bradykinin B2 receptors. The clinical relevance of the present findings remains unclear; however, the fact that the ACE inhibitor, but not the angiotensin II type 1 receptor antagonist, enhanced the action of bradykinin on sympathetic neurotransmission may warrant further investigation.

Bradykinin facilitates noradrenaline spillover during contraction in the canine gracilis muscle

Noradrenaline spillover from skeletal muscle vascular areas increases during exercise but the underlying mechanisms are not well understood. Muscle contraction itself causes changes in many factors that could affect noradrenaline spillover. For instance, it has been reported that bradykinin is synthesized in skeletal muscle areas during contraction. Because the B2 bradykinin receptor facilitates noradrenaline spillover, it may be involved in the increase associated with contraction. In this experiment, we studied the effect of bradykinin on noradrenaline spillover in the in situ canine gracilis muscle, using the specific B2 antagonist HOE 140. The drug did not modify noradrenaline spillover at rest, but did cause a significant decrease during muscle contraction, from 558 to 181 pg·min–1. As reported previously in the literature, fractional extraction of noradrenaline decreased during muscle contraction. This effect was independent of HOE 140 treatment. In light of our results, it seems that bradykinin formation during muscle contraction may play an important part in the observed increase in noradrenaline spillover but does not affect fractional extraction.Key words: skeletal muscle, fractional extraction, stimulation, HOE 140, B2 receptors.

Presynaptic regulation of cardiac norepinephrine release in ischemia

In myocardial ischemia presynaptic regulation of norepinephrine release may be altered either by ischemic effects on presynaptic receptor signaling or by ischemia-evoked accumulation of endogenous agonists. Because presynaptic receptors are targets of several drugs. such alterations may have pharmacotherapeutic implications. We investigated the effect of brief ischemic periods on presynaptic regulation of norepinephrine release by alpha2-adrenoceptors, beta2-adrenoceptors, adenosine A1-, angiotensin AT1-, and bradykinin B2-receptors in isolated perfused rat hearts. Exocytotic norepinephrine release was evoked by electrical field stimulation. Paired stimulations were performed to compare the pharmacologic intervention (S2) with the release under baseline conditions (S1), and the effects of receptor agonists and antagonists were compared under nonischemic and stop-flow conditions. In summary. during brief myocardial ischemia, presynaptic modulation of norepinephrine release is differentially regulated. Autoinhibitory alpha2-adrenoceptors lose their activity, whereas stimulatory beta2-adrenoceptors are sensitized. Inhibitory adenosine A1-receptors gain importance during ischemia owing to endogenous adenosine formation. Bradykinin- and angiotensin-mediated stimulation of norepinephrine release is not affected under ischemic conditions.

Effects of bradykinin on renal nerve stimulation-induced antidiuresis and norepinephrine overflow in anesthetized dogs

We examined effects of bradykinin on antidiuresis and norepinephrine overflow induced by renal nerve stimulation (RNS) in anesthetized dogs, with or without blockade of the B2 receptor by Hoe 140 (D-Arg-[Hyp3, Thi5, D-Tic7, Oic8]bradykinin) or the endogenous nitric oxide generation by N(G)nitro-L-arginine (NOARG), a nitric oxide synthase inhibitor. RNS (0.5-2.0 Hz) produced significant decreases in urine flow, urinary and fractional excretions of sodium, and increases in norepinephrine secretion rate (NESR), without affecting systemic and renal hemodynamics. Intrarenal arterial infusion of bradykinin (5 ng/kg per minute) significantly suppressed the RNS-induced antidiuresis and increase in NESR. Hoe 140 (100 ng/kg per minute) did not affect the RNS-induced renal actions, but in the presence of Hoe 140, bradykinin-induced suppressive actions on reductions in urine formation and increases in NESR in response to RNS were abolished. RNS during intrarenal arterial infusion of NOARG (40 microg/kg per minute) led to potent reductions in urine formation and decreased renal blood flow and glomerular filtration rate. Simultaneously, NESR was markedly increased. During NOARG infusion, bradykinin-induced decreases in renal actions elicited by RNS were markedly attenuated. These findings suggest that bradykinin suppresses the RNS-induced norepinephrine overflow and renal actions via nitric oxide production mediated by activation of B2 receptor. Renal noradrenergic neurotransmission may be inhibited by bradykinin at the prejunctional level, when its local production in the kidney is enhanced.

Renin-angiotensin system inhibition on noradrenergic nerve terminal function in pacing-induced heart failure

Chronic angiotensin-converting enzyme (ACE) inhibition has been shown to improve cardiac sympathetic nerve terminal function in heart failure. To determine whether similar effects could be produced by angiotensin II AT(1) receptor blockade, we administered the ACE inhibitor quinapril, angiotensin II AT(1) receptor blocker losartan, or both agents together, to rabbits with pacing-induced heart failure. Chronic rapid pacing produced left ventricular dilation and decline of fractional shortening, increased plasma norepinephrine (NE), and caused reductions of myocardial NE uptake activity, NE histofluorescence profile, and tyrosine hydroxylase immunostained profile. Administration of quinapril or losartan retarded the progression of left ventricular dysfunction and attenuated cardiac sympathetic nerve terminal abnormalities in heart failure. Quinapril and losartan together produced greater effects than either agent alone. The effect of renin-angiotensin system inhibition on improvement of left ventricular function and remodeling, however, was not sustained. Our results suggest that the effects of ACE inhibitors are mediated via the reduction of angiotensin II and that angiotensin II plays a pivotal role in modulating cardiac sympathetic nerve terminal function during development of heart failure. The combined effect of ACE inhibition and angiotensin II AT(1) receptor blockade on cardiac sympathetic nerve terminal dysfunction may contribute to the beneficial effects on cardiac function in heart failure.

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.

Augmented sympathetic response to bradykinin in the diabetic heart before autonomic denervation

We studied whether diabetes mellitus affects the bradykinin (BK)-induced release of norepinephrine (NE) from rat cardiac sympathetic endings in situ. Three groups were studied. Group A (n=12) was rendered diabetic with streptozotocin (STZ), group B (n=13) received STZ and insulin, and group C (n=14) received citrate buffer only. NPH insulin was given to group B from day 7 after STZ. Atria were paced (3Hz) with rectangular voltage pulses at mechanical threshold intensity (0.15 V/cm). The release of NE was assessed through its effects on contractile force in the presence of atropine (1 micromol/L). Intensifying the field stimulation above the neural threshold ( approximately 0.4 V/cm) produced a graded positive inotropic effect that was due to the release of NE from sympathetic nerve endings. The additional effect of 0.1 micromol/L BK on the force of contraction was determined at half-maximal neural stimulation (ie, at approximately 0.65 V/cm). Then, after washing out BK and lowering the stimulation intensity to mechanical threshold, a cumulative dose-response curve for added NE was generated, allowing the positive inotropic effects of neural stimulation (with or without BK) to be expressed in terms of an equivalent inotropic concentration of added NE ([NE(eq)]). Neural stimulation, in the absence of BK, gave an [NE(eq)] of 32+/-3 nmol/L in group A, 44+/-6 nmol/L in group B, and 37+/-6 nmol/L in group C. BK increased [NE(eq)] by a factor of 6.2+/-0.9 in group A, 4.5+/-0.5 in group B, and 3.7+/-0.3 in group C. This factor was greater in group A than in group C but indistinguishable in groups B and C. Atria from normal and diabetic rats were incubated in (3)[H]NE for 60 minutes. Excess tracer was removed, and atria were stimulated during a series of 1-minute episodes at half-maximal neural stimulation to cause exocytotic (3)[H]NE release. BK augmented (3)[H]NE release in normal (n=4) and in diabetic (n=4) atria. This BK-induced increase of (3)[H]NE overflow (expressed as a fraction of tissue (3)[H]NE radioactivity) was 4 times greater in diabetic than in normal preparations. The response to BK in releasing sympathetic neurotransmitter is augmented in diabetic rats, recovering in a manner dependent on insulin.

Modulation of (3)H-noradrenaline release by presynaptic opioid, cannabinoid and bradykinin receptors and beta-adrenoceptors in mouse tissues

Release-modulating opioid and cannabinoid (CB) receptors, beta-adrenoceptors and bradykinin receptors at noradrenergic axons were studied in mouse tissues (occipito-parietal cortex, heart atria, vas deferens and spleen) preincubated with (3)H-noradrenaline. Experiments using the OP(1) receptor-selective agonists DPDPE and DSLET, the OP(2)-selective agonists U50488H and U69593, the OP(3)-selective agonist DAMGO, the ORL(1) receptor-selective agonist nociceptin, and a number of selective antagonists showed that the noradrenergic axons innervating the occipito-parietal cortex possess release-inhibiting OP(3) and ORL(1) receptors, those innervating atria OP(1), ORL(1) and possibly OP(3) receptors, and those innervating the vas deferens all four opioid receptor types. Experiments using the non-selective CB agonists WIN 55,212-2 and CP 55,940 and the CB(1)-selective antagonist SR 141716A indicated that the noradrenergic axons of the vas deferens possess release-inhibiting CB(1) receptors. Presynaptic CB receptors were not found in the occipito-parietal cortex, in atria or in the spleen. Experiments using the non-selective beta-adrenoceptor agonist isoprenaline and the beta(2)-selective agonist salbutamol, as well as subtype-selective antagonists, demonstrated the occurrence of release-enhancing beta(2)-adrenoceptors at the sympathetic axons of atria and the spleen, but demonstrated their absence in the occipito-parietal cortex and the vas deferens. Experiments with bradykinin and the B(2)-selective antagonist Hoe 140 showed the operation of release-enhancing B(2) receptors at the sympathetic axons of atria, the vas deferens and the spleen, but showed their absence in the occipito-parietal cortex. The experiments document a number of new presynaptic receptor locations. They confirm and extend the existence of marked tissue and species differences in presynaptic receptors at noradrenergic neurons.

Dose-dependent cardiovascular and neuromuscular effects of stonefish (Synanceja trachynis) venom

There has been recent debate regarding the labile nature of stonefish venoms and the pharmacology of their breakdown products. The present study examined the cardiovascular and neuromuscular effects of lyophilised venom, and conducted a preliminary investigation of freshly milked venom. Lyophilised venom (20 microg/ml) caused endothelium-dependent relaxation in rat aortae that was abolished by atropine (0.1 microM). In contrast, an endothelium-independent contractile response occurred in porcine coronary arteries. However, in the presence of atropine (10 nM), this became a relaxation response which was attenuated by the B2 antagonist FR-173657 (0.1 microM) or by a combination of idazoxan (1 microM) and propranolol (1 microM). In rat isolated atria, lyophilised venom (4 microg/ml) caused a biphasic inotropic response consisting of an initial decrease, and then increase, in force which were attenuated by atropine (0.5 microM) and propranolol (5 microM), respectively. The increase in force produced by venom was unaffected by reserpine pre-treatment suggesting a direct action at adrenoceptors. In the anaesthetised rat, lyophilised venom (1-300 microg/kg, i.v.), caused a dose-dependent depressor response, with a subsequent pressor response at higher concentrations (30-300 microg/kg, i.v.). In the presence of atropine (1 mg/kg, i.v.), the depressor response to venom was abolished, a transient pressor response unmasked and the secondary pressor response augmented. In the additional presence of prazosin (50 microg/kg, i.v.), the transient pressor response was abolished and the secondary pressor response attenuated. Lyophilised venom had no significant effect on nerve-evoked (10 microg/ml) or directly-evoked (100 microg/ml) twitches of the chick biventer cervicis muscle preparation. Milked venom (1 microl/ml) caused a biphasic response (i.e., an initial relaxation followed by contraction) in rat aortae, a contraction in porcine coronary arteries, complete cessation of rat isolated atrial activity and markedly inhibited both nerve-evoked and directly-evoked twitches of the chick biventer cervicis muscle preparation. In the anaesthetised rat, milked venom (15 microl/kg, i.v.) caused immediate cardiovascular collapse. It appears that the cardiovascular effects of stonefish venom are mediated by a dose-dependent action at muscarinic receptors and adrenoceptors.

Enhancement of noradrenaline release by angiotensin II and bradykinin in mouse atria: evidence for cross-talk between G(q/11) protein- and G(i/o) protein-coupled receptors

1. The interaction between alpha(2)-autoreceptors and receptors for angiotensin (AT(1)) and bradykinin (B(2)) was studied in mouse isolated atria. The preparations were labelled with [(3)H]-noradrenaline and then superfused with desipramine-containing medium and stimulated electrically. 2. Angiotensin II (10(-11) - 10(-7) M), angiotensin III (10(-10) - 10(-6) M) and bradykinin (10(-11) - 10(-7) M) enhanced the evoked overflow of tritium when preparations were stimulated with conditions that led to marked alpha(2)-autoinhibition (120 pulses at 3 Hz), but not when stimulated with conditions that led to little alpha(2)-autoinhibition (20 pulses at 50 Hz). 3. Blockade of alpha-adrenoceptors by phentolamine (1 or 10 microM) reduced or abolished the effect of angiotensin II and bradykinin on the overflow response to 120 pulses at 3 Hz. 4. Addition of the delta-opioid agonist [D-Ser(2)]-leucine enkephalin-Thr (DSLET, 0.1 microM), or of neuropeptide Y (0.1 microM), together with phentolamine, restored the effect of angiotensin II and bradykinin. 5. The beta-adrenoceptor agonist terbutaline (10(-9) - 10(-4) M) enhanced the evoked overflow of tritium irrespective of the degree of autoinhibition. 6. The experiments show that (i) a marked prejunctional facilitatory effect of angiotensin and bradykinin in mouse isolated atria requires prejunctional alpha(2)-autoinhibition; (ii) in the absence of alpha(2)-autoinhibition, activation of other prejunctional G(i/o) protein-coupled receptors, namely opioid and neuropeptide Y receptors, restores a marked effect of angiotensin II and bradykinin; and (iii) the facilitatory effect of terbutaline is not dependent upon the degree of alpha(2)-autoinhibition. The findings indicate that the major part of the release-enhancing effect elicited through prejunctional G(q/11) protein-coupled receptors is due to disruption of an ongoing, alpha(2)-autoreceptor-triggered G(i/o) protein mediated inhibition.

Dilated and failing cardiomyopathy in bradykinin B(2) receptor knockout mice

BACKGROUND

The activation of B(2) receptors by kinins could exert cardioprotective effects in myocardial ischemia and heart failure.

METHODS AND RESULTS

To test whether the absence of bradykinin B(2) receptors may affect cardiac structure and function, we examined the developmental changes in blood pressure (BP), heart rate, and heart morphology of bradykinin B(2) receptor gene knockout (B(2)(-/-)), heterozygous (B(2)(+/-)), and wild-type (B(2)(+/+)) mice. The BP of B(2)(-/-) mice, which was still normal at 50 days of age, gradually increased, reaching a plateau at 6 months (136+/-3 versus 109+/-1 mm Hg in B(2)(+/+), P<0.01). In B(2)(+/-) mice, BP elevation was delayed. At 40 days, the heart rate was higher (P<0.01) in B(2)(-/-) and B(2)(+/-) than in B(2)(+/+) mice, whereas the left ventricular (LV) weight and chamber volume were similar among groups. Thereafter, the LV growth rate of B(2)(-/-) and B(2)(+/-) mice was accelerated, leading at 360 days to a LV weight-to-body weight ratio that was 9% and 17% higher, respectively, than that of B(2)(+/+) mice. In B(2)(-/-) mice, hypertrophy was associated with a marked chamber dilatation (42% larger than that of B(2)(+/+) mice), an elevation in LV end-diastolic pressure (25+/-3 versus 5+/-1 mm Hg in B(2)(+/+) mice, P<0.01), and reparative fibrosis.

CONCLUSIONS

The disruption of the bradykinin B(2) receptor leads to hypertension, LV remodeling, and functional impairment, implying that kinins are essential for the functional and structural preservation of the heart.