Changes in bradykinin level in coronary sinus blood after the experimental occlusion of a coronary artery

Excitatory effect of bradykinin on intrinsic neurons of the rat heart

The heart receives sympathetic and parasympathetic innervation through the intrinsic cardiac nervous system. Although bradykinin (BK) has negative inotropic and chronotropic properties of cardiac contraction, the direct effect of BK on the intrinsic neural network of the heart is still unclear. In the present study, the effect of BK on the intracardiac ganglion neurons isolated from rats was investigated using the perforated patch-clamp technique. Under current-clamp conditions, application of 0.1 μM BK depolarized the membrane, accompanied by repetitive firing of action potentials. When BK was applied repeatedly, the second responses were considerably less intense than the first application. The BK action was fully inhibited by the B₂ receptor antagonist Hoe-140, but not by the B₁ receptor antagonist des-Arg⁹-[Leu⁸]-BK. The BK response was mimicked by the B₂ agonist [Hyp³]-BK. The BK-induced depolarization was inhibited by the phospholipase C inhibitor U-73122. BK evoked inward currents under voltage-clamp conditions at a holding potential of -60 mV. Removal of extracellular Ca²⁺ markedly increased the BK-induced currents, suggesting an involvement of Ca²⁺-permeable non-selective cation channels. The muscarinic agonist oxotremorine-M (OxoM) also elicited the extracellular Ca²⁺-sensitive cationic currents. The OxoM response did not exhibit rundown with repeated agonist application. The amplitude of current evoked by 1 μM OxoM was comparable to that induced by 0.1 μM BK. Co-application of 0.1 μM BK and 1 μM OxoM elicited the current whose peak amplitude was almost the same as that elicited by OxoM alone, suggesting that BK and OxoM activate same cation channels. BK also reduced the amplitude of M-current, while the M-current inhibitor XE-991 affected neither resting membrane potential nor the BK-induced depolarization. From these results, we suggest that BK regulates excitability of intrinsic cardiac neurons by both an activation of non-selective cation channels and an inhibition of M-type K⁺ channels through B₂ receptors.

Intrapericardial capsaicin and bradykinin induce different cardiac-somatic and cardiovascular reflexes in rats

Patients with myocardial infarction experience various types of chest pain and autonomic disturbance symptoms. Studies in rats have shown that pericardial infusions of certain chemicals induce cardiac-related muscle pain and cardiovascular reflexes. In the present study, bradykinin or capsaicin was injected into the pericardial sac and the resulting cardiac-somatic reflexes and blood pressure (BP) alterations were record. We found that the cardiac-somatic reflex induced by bradykinin had a longer latency, shorter duration, and lower firing rate than that induced by capsaicin (p<0.05). We also found that bradykinin induced a hypertensive response (p<0.05), while capsaicin induced a hypotensive response (p<0.05). Bilateral vagotomy had no effect on the cardiac-somatic reflex induced by bradykinin (p>0.05) but reduced the reflex induced by capsaicin (p<0.05). However, vagotomy had no effect on the BP alterations induced by both bradykinin and capsaicin (p>0.05). These results suggest that bradykinin and capsaicin activate different pathways to induce cardiac-somatic and cardiovascular reflexes and that the vagus nerve is involved in TRPV1-related muscle pain modulation.

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.

Different cardiac tissue plasminogen activator release patterns by local stimulation of the endothelium and sympathetic nerves in pigs

Myocardial ischemia induces cardiac tissue plasminogen activator (tPA) release, declining by repeated periods of ischemia. However, the mechanisms and cellular sources are unknown. Sympathetic nerve stimulation (SS) and bradykinin (BK), an endogenous inducer of endothelial tPA release, may play roles, potentially involving different sources or mechanisms revealed by different release patterns. Therefore, we compared the cardiac tPA release patterns during repeated coronary BK infusions and SS, both with an ensuing period of local myocardial ischemia/reperfusion (I/R). Nine pigs were subjected to four periods of coronary BK infusion (4 min) and another nine animals to four periods of SS (4 min). Finally, 10 min of I/R was induced in both groups. The single-peaked BK-induced tPA release declined toward baseline by repeated infusions, but tPA release reappeared during I/R. In contrast, total tPA release during repeated SS and subsequent I/R was more stable, and SS-induced total tPA and norepinephrine (NE) releases were strongly correlated. Surprisingly, the instantaneous SS-induced tPA release was biphasic with a stable first peak, and a second peak declining toward baseline by repeated stimulations. The fluctuations in cardiac release of plasminogen activator inhibitor-1 and the endogenous BK inhibitor angiotensin-converting enzyme, could not explain the diverging tPA release patterns. Different tPA release patterns were demonstrated during SS and BK stimulation, as well as diverging responses to repeated stimulations and subsequent I/R. This study demonstrates strong association between tPA and NE during SS and possibly two different sources or mechanisms for SS-induced tPA release.

Bradykinin and thromboxane A2 reciprocally interact to synergistically stimulate cardiac spinal afferents during myocardial ischemia

Myocardial ischemia is a complex process leading to the simultaneous release of a number of mediators, including thromboxane A(2) (TxA(2)) and bradykinin (BK), that activate cardiac spinal afferents. The present study tested the hypothesis that TxA(2) and BK reciprocally interact to excite ischemically sensitive cardiac afferents. Nerve activity of single cardiac afferent units was recorded from the left sympathetic chain or rami communicantes (T(2)-T(5)) of anesthetized cats. Fifty-two ischemically sensitive afferents (conduction velocity = 0.27-3.35 m/s, 7 Adelta-fibers and 45 C-fibers) were identified. Repeated injections (1 microg) of BK into the left atrium (LA) 4 min after the administration of U-46619 (5 microg into the LA), a TxA(2) mimetic, induced a significantly larger cardiac afferent response than the first response to BK (0.61 +/- 0.14 to 1.95 +/- 0.29 vs. 0.66 +/- 0.09 to 2.75 +/- 0.34 impulses/s, first injection vs. second injection, n = 8). Conversely, blockade of TxA(2) receptors with BM-13,177 (30 mg/kg iv) attenuated the responses of eight other afferents to BK (1 microg into the LA) by 45%. In contrast, repeated BK (1 microg into the LA) induced consistent discharge activity in six separate afferents. We then observed that the coadministration of U-46619 (5 microg) and BK (1 microg into the LA) together caused a total response that was significantly higher than the predicted response by the simple addition of the individual responses. BK (1 microg) facilitated eight cardiac afferent responses to U-46619 (5 microg into the LA) by 64%. In contrast, repeated U-46619 (5 microg into the LA) without intervening BK stimulation evoked consistent responses in seven other ischemically sensitive afferents. Finally, inhibition of cyclooxygenase with indomethacin (5 mg/kg iv) eliminated the potentiating effects of BK on the cardiac afferent response to U-46619 (5 microg into the LA) but did not alter the afferent response to U-46619. These data suggest that BK and TxA(2) reciprocally interact to stimulate ischemically sensitive cardiac afferent endings leading to synergistic afferent responses and that the BK sensitization effect is mediated by cyclooxygenase products.

Regulation of cardiac afferent excitability in ischemia

The heart at the time of Sir William Harvey originally was thought to be an insensate organ. Today, however, we know that this organ is innervated by sensory nerves that course centrally though mixed nerve pathways that also contain parasympathetic or sympathetic motor nerves. Angina or cardiac pain is now well recognized as a pressure-like pain that occurs during myocardial ischemia when coronary artery blood flow is interrupted. Sympathetic (or spinal) afferent fibers that are either finely myelinated or unmyelinated are responsible for the transmission of information to the brain that ultimately allows the perception of angina as well as activation of the sympathetic nervous system, resulting in tachycardia, hypertension, and sometimes arrhythmias. Although early studies defined the importance of the vagal and sympathetic cardiac afferent systems in reflex autonomic control, until recently there has been little appreciation of the mechanisms of activation of the sensory endings. This review examines the role of a number of chemical mediators and their sources that are activated by the ischemic process. In this regard, patients with ischemic syndromes, particularly myocardial infarction and unstable angina, are known to have platelet activation, which leads to release of a number of chemical mediators, including serotonin, histamine, and thromboxane A(2), all of which stimulate ischemically sensitive cardiac spinal afferent endings in the ventricles through specific receptor-mediated processes. Furthermore, protons from lactic acid, bradykinin, and reactive oxygen species, especially hydroxyl radicals, individually and frequently in combination, stimulate these endings during ischemia. Cyclooxygenase products appear to sensitize the endings to the action of bradykinin and histamine. These studies of the chemical mechanisms of activation of cardiac sympathetic afferent endings during ischemia have the potential to provide targeted therapies that can modify the angina and the deleterious reflex responses that have the potential to exacerbate ischemia and myocardial cell death.

Characterization of thoracic spinal neurons with noxious convergent inputs from heart and lower airways in rats

Respiratory symptoms experienced in some patients with cardiac diseases may be due to convergence of noxious cardiac and pulmonary inputs onto neurons of the central nervous system. For example, convergence of cardiac and respiratory inputs onto single solitary tract neurons may be in part responsible for integration of regulatory and defensive reflex control. However, it is unknown whether inputs from the lungs and heart converge onto single neurons of the spinal cord. The present aim was to characterize upper thoracic spinal neurons responding to both noxious stimuli of the heart and lungs in rats. Extracellular potentials of single thoracic (T3) spinal neurons were recorded in pentobarbital anesthetized, paralyzed, and ventilated male rats. A catheter was placed in the pericardial sac to administer bradykinin (BK, 10 microg/ml, 0.2 ml, 1 min) as a noxious cardiac stimulus. The lung irritant, ammonia, obtained as vapor over a 30% solution of NH(4)OH was injected into the inspiratory line of the ventilator (0.5-1.0 ml over 20 s). Intrapericardial bradykinin (IB) altered activity of 58/65 (89%) spinal neurons that responded to inhaled ammonia (IA). Among those cardiopulmonary convergent neurons, 81% (47/58) were excited by both IA and IB, and the remainder had complex response patterns. Bilateral cervical vagotomy revealed that vagal afferents modulated but did not eliminate responses of individual spinal neurons to IB and IA. The convergence of pulmonary and cardiac nociceptive signaling in the spinal cord may be relevant to situations where a disease process in one organ influences the behavior of the other.

Kallidin-like peptide mediates the cardioprotective effect of the ACE inhibitor captopril against ischaemic reperfusion injury of rat heart

1. The potential cardioprotective effect of ACE inhibitors has been attributed to the inhibition of bradykinin degradation. Recent data in rats documented a kallidin-like peptide, which mimics the cardioprotective effect of ischaemic preconditioning. This study investigates in isolated Langendorff rat heart the effect of the ACE inhibitor captopril, the role of bradykinin, kallidin-like peptide, and nitric oxide (NO). 2. The bradykinin level in the effluent of the control group was 14.6 pg ml(-1) and was not affected by captopril in the presence or absence of kinin B2-receptor antagonist, HOE140. 3. The kallidin-like peptide levels were approximately six-fold higher (89.8 pg ml(-1)) and increased significantly by treatment with captopril (144 pg ml(-1)), and simultaneous treatment with captopril and HOE140 (197 pg ml(-1)). 4. Following 30 min ischaemia in the control group, the creatine kinase activity increased from 0.4 to 53.4 U l(-1). In the captopril group and in the captopril+L-NAME group, the creatine kinase activity was significantly lower (18.5 and 22.8 U l(-1)). This beneficial effect of captopril was completely abolished by the kinin B2-receptor antagonist, HOE140, as well as by the kallidin antiserum. 5. Perfusion of the hearts with kallidin before the 30 min ischaemia, but not with bradykinin, yielded an approximately 50% reduction in creatine kinase activity after reperfusion. 6. Pretreatment with L-NAME alone and simultaneously with captopril, and with kallidin, respectively, suggests a kinin-independent action of NO before the 30 min ischaemia on coronary flow and a kinin-dependent action after ischaemia. 7. These data show that captopril increases kallidin-like peptide in the effluent. Kallidin-like peptide via kinin B2 receptor seems to be the physiological mediator of cardioprotective actions of captopril against ischaemic reperfusion injury. HOE140 as well as the kallidin antiserum abolished the cardioprotective effects of captopril.

A kallidin-like peptide is a protective cardiac kinin, released by ischaemic preconditioning of rat heart

Bradykinin is thought to play a major role among the endogenous cardioprotective candidates of ischaemic preconditioning (IPC). Little attention has been paid to the fact that in the tissue kallidin (KAL), rather than bradykinin might be the physiological mediator of the kallikrein-kinin system. In order to evaluate the importance of one or the other peptide the release and effect of both kinins has been investigated in isolated rat hearts following IPC. Bradykinin- and a KAL-like peptide were measured in the effluent of the rat isolated Langendorff heart with two different specific radioimmunoassays. The creatine kinase activity in the effluent was judged as degree of cardiac injury caused by ischaemia. During IPC, which consists of three 5 min no-flow and 5 min reperfusion cycles prior to the 30 min ischaemia, the bradykinin level in the effluent did not change significantly (15.4-19.4 pg ml(-1)). In the control group the bradykinin levels were 15.9-16.6 pg ml(-1). During IPC KAL-like peptide (Arg(1)-, instead of Lys(1)-KAL), which has recently been verified by mass spectrometry, displays 5.8-fold higher levels in the effluent and significantly increases in the same time interval from 90.4 to 189 pg ml(-1). After 30 min ischaemia the bradykinin levels in the IPC group were not significantly different to those of the control group (18.7 vs 14.4 pg ml(-1)). The KAL-like peptide levels in the IPC group vs the control group were 105 vs 86.1 pg ml(-1). By the 30 min ischaemia the creatine kinase activity in the IPC group increased from 0.367 to 8.93 U l(-1) (before and 10-30 min after ischaemia). In the control group during the same time period the creatine kinase levels increased from 0.277 to 34.9 U l(-1). The low increase in creatine kinase activity following IPC was taken as equivalent of the cardioprotective action. A KAL antibody or HOE140 (kinin B(2)-receptor antagonist) completely abolished this beneficial effect of IPC (36.6 and 53.0 U l(-1)) when added to the perfusion medium during the reperfusion cycles of IPC prior to the 30 min ischaemia. Our data suggest that in rat hearts KAL-like peptide rather than bradykinin is the physiological compound activated by IPC and acting via the cardiac kinin B(2)-receptor. Thus, endogenously generated KAL-like peptide seems to play a major role in the cardioprotection of IPC.

Interactions between histamine and bradykinin in stimulation of ischaemically sensitive cardiac afferents in felines

Cardiac spinal afferents are activated during myocardial ischaemia. Our previous studies have shown that during ischaemia, histamine and bradykinin (BK) stimulate cardiac spinal afferents. Because the two mediators are released together during ischaemia, the present study examined the interactions between these two mediators with respect to their influence on ischaemically sensitive cardiac afferents. Single-unit cardiac afferent activity was recorded from the left sympathetic chain or rami communicantes (T(2)-T(5)) in anaesthetized cats. Fifty-five ischaemically sensitive cardiac afferents (conduction velocity (CV) = 0.2-5.6 m s(-1), 8 Adelta- and 47 C-fibres) were identified. Administration of histamine (10 microg kg(-1)) and BK (1 microg) in combination into the left atrium (LA) caused an additive response in 16 afferents compared with administration of either BK or histamine alone (2.62 +/- 0.39 versus 1.67 +/- 0.20 versus 1.24 +/- 0.23 impulses s(-1) (imp s(-1)), BK + histamine versus BK versus histamine). To further evaluate interactions between these mediators, we observed that injection of histamine (10 microg kg(-1), LA) 4 min after the administration of BK (1 microg, LA) induced a significantly larger cardiac afferent response than the response to histamine before BK (1.24 +/- 0.23 versus 1.96 +/- 0.39 imp s(-1), before versus after, n = 10). In contrast, six other afferents responded reproducibly to repeated injections of histamine (10 microg kg(-1), LA) in the absence of BK. BK sensitization of the afferent response to histamine lasted for less than 10 min. Cyclooxygenase blockade with indomethacin (5 mg kg(-1), i.v.) abolished BK sensitization of the response to histamine (1.09 +/- 0.11 versus 1.11 +/- 0.10 imp s(-1), n = 10). Conversely, the response of most (7/9) cardiac afferents to repeat application of BK (1 microg, LA) 4 min after histamine (10 microg kg(-1), LA) was attenuated compared with the BK response before histamine (1.84 +/- 0.25 versus 1.31 +/- 0.18 imp s(-1), before versus after, P < 0.05). Repeat BK (1 microg, LA) induced a consistent response in five other afferents in the absence of histamine. Thus, BK interacts with histamine, and together they cause a larger response than either one alone. BK sensitizes cardiac afferents responding to histamine in a time-dependent fashion, and the BK sensitization effect is dependent on an intact cyclooxygenase pathway. Conversely, histamine reduces the response of most afferents to BK.

c-Fos expression in rat brain stem and spinal cord in response to activation of cardiac ischemia-sensitive afferent neurons and electrostimulatory modulation

The purpose of this study was to identify central neuronal sites activated by stimulation of cardiac ischemia-sensitive afferent neurons and determine whether electrical stimulation of left vagal afferent fibers modified the pattern of neuronal activation. Fos-like immunoreactivity (Fos-LI) was used as an index of neuronal activation in selected levels of cervical and thoracic spinal cord and brain stem. Adult Sprague-Dawley rats were anesthetized with urethane and underwent intrapericardial infusion of an “inflammatory exudate solution” (IES) containing algogenic substances that are released during ischemia (10 mM adenosine, bradykinin, prostaglandin E2, and 5-hydroxytryptamine) or occlusion of the left anterior descending coronary artery (CoAO) to activate cardiac ischemia-sensitive (nociceptive) afferent fibers. IES and CoAO increased Fos-LI above resting levels in dorsal horns in laminae I–V at C2 and T4 and in the caudal nucleus tractus solitarius. Dorsal rhizotomy virtually eliminated Fos-LI in the spinal cord as well as the brain stem. Neuromodulation of the ischemic signal by electrical stimulation of the central end of the left thoracic vagus excited neurons at the cervical and brain stem level but inhibited neurons at the thoracic spinal cord during IES or CoAO. These results suggest that stimulation of the left thoracic vagus excites descending inhibitory pathways. Inhibition at the thoracic spinal level that suppresses the ischemic (nociceptive) input signal may occur by a short-loop descending pathway via signals from cervical propriospinal circuits and/or a longer-loop descending pathway via signals from the nucleus tractus solitarius.

Lack of association of a 9 bp insertion/deletion polymorphism within the bradykinin 2 receptor gene with myocardial infarction

The BK (bradykinin) B2 receptor is the major cellular mediator of the effects of BK. A 9 bp deletion in the promoter of the receptor gene represents an allelic variant that is associated with enhanced mRNA expression levels. We tested whether this polymorphism is associated with the prevalence of MI (myocardial infarction) or with echocardiographically determined left ventricular function in post-MI patients. Patients with documented MI (n=484), matched controls and controls without evidence of coronary heart disease (n=1363) constituted cases and controls. MI patients and controls were carefully matched for age, gender and cardiovascular risk factors. Genotype distributions of the 9 bp insertion/deletion polymorphism were similar across the groups: −9/−9, −9/+9 and +9/+9 were 22.1, 49.5 and 28.5% in MI patients, and 23.0, 44.6 and 32.5% in matched control subjects respectively. The lack of association was also observed in selected subgroups, stratified by age, gender and cardiovascular risk factors. Furthermore, there was no relation between this polymorphism and left ventricular systolic function in post-MI patients. These findings indicate that the 9 bp insertion/deletion polymorphism of the BK B2 receptor gene is neither related to the prevalence of MI nor to left ventricular function after MI.

Myocardial ischemia induces the release of substance P from cardiac afferent neurons in rat thoracic spinal cord

Antibody-coated microprobes were inserted into the thoracic (T3-4) spinal cord in urethane-anesthetized Sprague-Dawley rats to detect the differences in the release of immunoreactive substance P-like (irSP) substances in response to differential activation of cardiac nociceptive sensory neurons (CNAN). CNAN were stimulated either by intrapericardial infusion of an inflammatory ischemic exudate solution (IES) containing algogenic substances (i.e., 10 mM each of adenosine, bradykinin, prostaglandin E2, and 5-hydroxytryptamine), or by transient occlusion of the left anterior descending coronary artery (CoAO). There was widespread basal release of irSP from the thoracic spinal cord. Stimulation of the CNAN by IES did not alter the pattern of release of irSP. Conversely, CoAO augmented the release of irSP from T3-4 spinal segments from laminae I-VII. This CoAO-induced irSP release was eliminated after thoracic dorsal rhizotomy. These results indicate that heterogeneous activation of cardiac afferents, as with focal coronary artery occlusion, represents an optimum input for activation of the cardiac neuronal hierarchy and for the resultant perception of angina. Excessive stimulation of cardiac nociceptive afferent neurons elicited during regional coronary artery occlusion involves the release of SP in the thoracic spinal cord and suggests that local spinal cord release of SP may be involved in the neural signaling of angina.

Surgery modifies cardiac sensory transduction

OBJECTIVE

We sought to determine whether cardiac surgery, specifically the placement of an incision within a ventricular wall, affects the capacity of regional cardiac sensory nerve terminals (neurites) to transduce the local cardiac milieu.

METHODS

The capacity of sensory neurites in the right ventricular outflow tract associated with afferent neurons in nodose ganglia to transduce their mechanical and chemical milieu was studied in 11 anesthetized pigs before and after performing a local ventriculotomy.

RESULTS

Right ventricular outflow tract sensory neurites associated with 23 nodose ganglion afferent neurons were identified that transduced local mechanical deformation along with substance P. The capacity of these sensory neurites to transduce these stimuli was almost totally obtunded after local ventriculotomy.

CONCLUSIONS

The capacity of afferent neurons to transduce the cardiac milieu can be modified by cardiac surgical interventions. This may have negative implications with respect to how the entire cardiac neuronal hierarchy transduces alterations in the cardiac milieu postsurgery. This fact should be taken into account when contemplating the placement of cardiac incisions during surgery.

Cardiac kinin level in experimental diabetes mellitus: role of kininases

Diabetes mellitus impairs the cardiac kallikrein-kinin system by reducing cardiac kallikrein (KLK) and kininogen levels, a mechanism that may contribute to the deleterious outcome of cardiac ischemia in this disease. We studied left ventricular (LV) function and bradykinin (BK) coronary outflow in buffer-perfused, isolated working hearts (n = 7) of controls and streptozotocin (STZ)-induced diabetic rats before and after global ischemia. With the use of selective kininase inhibitors, the activities of angiotensin I-converting enzyme, aminopeptidase P, and neutral endopeptidase were determined by analyzing the degradation kinetics of exogenously administered BK during sequential coronary passages. Basal LV function and coronary flow were impaired in STZ-induced diabetic rats. Neither basal nor postischemic coronary BK outflow differed between control and diabetic hearts. Reperfusion after 15 min of ischemia induced a peak in coronary BK outflow that was of the same extent and duration in both groups. In diabetic hearts, total cardiac kininase activity was reduced by 41.4% with an unchanged relative kininase contribution compared with controls. In conclusion, despite reduced cardiac KLK synthesis, STZ-induced diabetic hearts are able to maintain kinin liberation under basal and ischemic conditions because of a primary impairment or a secondary downregulation of kinin-degrading enzymes.

Bradykinin B1 and B2 receptors differentially regulate cardiac Na+-H+ exchanger, Na+-Ca2+ exchanger and Na+-HCO3- symporter

Bradykinin B(1) and B(2) receptors are up-regulated in the infarcted myocardium, and both receptors are involved in the regulation of intracellular pH and Ca(2+). The present study investigated the role of bradykinin B(1) and B(2) receptors in the regulation of Na(+)-H(+) exchanger (NHE-1), Na(+)-Ca(2+) exchanger (NCE-1) and Na(+)-HCO(3)(-) symporter (NBC-1) in the infarcted myocardium. NHE-1, NCE-1 and NBC-1 mRNA expression was determined by Northern blot analysis and the protein levels by Western blot analysis. Measurements were performed 1, 7 and 14 days after induction of myocardial infarction. Localization of NHE-1, NCE-1 and NBC-1 within the myocardium was studied using confocal microscopy. Cardiac morphology was measured in picrosiris-red-stained hearts. Rats were treated with placebo, the bradykinin B(2) receptor antagonist icatibant (0.5 mg/kg/day) or the bradykinin B(1) receptor antagonist des-Arg(9)-[Leu(8)]bradykinin (1 mg/kg/day). Treatment was started 1 week prior to surgery and continued until 1, 7 and 14 days post infarction. NHE-1, NCE-1 and NBC-1 mRNA expression and protein levels were increased 1 day and reached maximum values on day 7 post infarction. NHE-1 was localized in the plasma membrane, NCE-1 in the membrane of the sarcoplasmatic reticulum and NBC-1 near the Z-line. Icatibant reduced NHE-1 and inhibited NCE-1 mRNA- and protein up-regulation, while des-Arg(9)-[Leu(8)]bradykinin had no effect on NHE-1 and NCE-1 expression and translation. Transcriptional and translational up-regulation of NBC-1 was unaffected by the bradykinin B(1) and B(2) receptor antagonists. Icatibant, but not des-Arg(9)-[Leu(8)]bradykinin, limited infarct size and reduced left ventricular dilation, septal thickening and interstitial fibrosis post infarction. Bradykinin B(2) receptors are involved in transcriptional and translational regulation of NHE-1 and NCE-1 in the ischemic myocardium. Chronic B(2) receptor blockade might exert an anti-ischemic effect via limitation of NHE-1-mediated acidosis and NCE-1-mediated Ca(2+)-overload.

Activation of a renin-angiotensin system in ischemic cardiac sympathetic nerve endings and its association with norepinephrine release

We had reported that in the ischemic heart, locally formed bradykinin (BK) and angiotensin II (Ang II) activate B2- and AT1-receptors on sympathetic nerve terminals (SNE), promoting reversal of the norepinephrine (NE) transporter in an outward direction (i.e., carrier-mediated NE release). Although both BK and Ang II contribute to ischemic NE release, Ang II is likely to play a more important role. Since BK is formed by ischemic SNE, we questioned whether cardiac SNE also contribute to local Ang II formation, in addition to being a target of Ang II. SNE were isolated from surgical specimens of human right atrium and incubated in ischemic conditions. These SNE released large amounts of endogenous NE via a carrier-mediated mechanism, as evidenced by the inhibitory effect of desipramine on this process. Moreover, two renin inhibitors, pepstatin-A and BILA 2157 BS, the ACE inhibitor enalaprilat and the AT1-receptor antagonist EXP3174 prevented ischemic NE release. Western blot analysis revealed the presence of renin in cardiac SNE. Renin abundance increased more than three-fold during ischemia. Thus, renin is present in cardiac SNE and is activated during ischemia, eventually culminating in Ang II formation, stimulation of AT1-receptors and carrier-mediated NE release. Our findings uncover a novel autocrine mechanism, by which Ang II, formed at SNE in myocardial ischemia, elicits carrier-mediated NE release by activating prejuntional AT1-receptors.

Regulation of cardiac bradykinin B1- and B2-receptor mRNA in experimental ischemic, diabetic, and pressure-overload-induced cardiomyopathy

Although kinins have been associated with the regulation of cardiovascular function in left ventricular hypertrophy (LVH) as a consequence of hypertension, myocardial infarction (MI), and/or diabetic cardiomyopathy, less is known about their receptor regulation under these conditions. We have therefore investigated the bradykinin B1-receptor (B1R) and B2-receptor (B2R) mRNA expression in rat models of MI, LVH and diabetes mellitus (DM). Sprague-Dawley rats (SD) were submitted to permanent ligation of the left descending coronary artery (LAD) to induce a MI, whereas DM was induced by a single injection of streptozotocin (STZ). LVH was induced after thoracic aortic banding (AB). Three weeks after MI, six weeks after STZ injection or six weeks after AB, left ventricular (LV) function was characterized using a Millar-tip catheter. Cardiac B1R- and B2R-mRNA expression were analyzed by specific RNase-protection assays (RPA). LV contractility (dP/dt max) was impaired by 40-48% in rats after induction of MI or DM compared to their controls. However, despite an enormous increase in LV end-diastolic pressure (LEVDP) to 310% after AB, LV contractility did not differ compared to the controls. These hemodynamic changes were accompanied by an up-regulation of cardiac B1R- (MI, 288%; STZ, 215%; AB, 4180%) and B2R-mRNA expression (MI, 122%; STZ, 288%; AB, 96%). Up-regulation of both BK-receptor (BKR) types in early stages of cardiac wound healing induced by ischemia and in chronic stages of cardiac remodeling induced by pressure-overload or by hyperglycemia indicates that kinins play a major role in the complex processes of cardiac tissue injury and repair.

Xanthine oxidase, but not neutrophils, contributes to activation of cardiac sympathetic afferents during myocardial ischaemia in cats

Activation of cardiac sympathetic afferents during myocardial ischaemia causes angina and induces important cardiovascular reflex responses. Reactive oxygen species (ROS) are important chemical stimuli of cardiac afferents during and after ischaemia. Iron-catalysed Fenton chemistry constitutes one mechanism of production of hydroxyl radicals. Another potential source of these species is xanthine oxidase-catalysed oxidation of purines. Polymorphonuclear leukocytes (PMNs) also contribute to the production of ROS in some conditions. The present study tested the hypothesis that both xanthine oxidase-catalysed oxidation of purines and neutrophils provide a source of ROS sufficient to activate cardiac afferents during ischaemia. We recorded single-unit activity of cardiac afferents innervating the ventricles recorded from the left thoracic sympathetic chain (T1-5) of anaesthetized cats to identify the afferents' responses to ischaemia. The role of xanthine oxidase in activation of these afferents was determined by infusion of oxypurinol (10 mg kg(-1), I.V.), an inhibitor of xanthine oxidase. The importance of neutrophils as a potential source of ROS in the activation of cardiac afferents during ischaemia was assessed by the infusion of a polyclonal antibody (3 mg ml(-1) kg(-1), I.V.) raised in rabbits immunized with cat PMNs. This antibody decreased the number of circulating PMNs and, to a smaller extent, platelets. Since previous data suggest that platelets release serotonin (5-HT), which activates cardiac afferents through a serotonin receptor (subtype 3,5-HT3 receptor) mechanism, before treatment with the antibody in another group, we blocked 5-HT3 receptors on sensory nerve endings with tropisetron (300 microg kg(-1), I.V.). We observed that oxypurinol significantly decreased the activity of cardiac afferents during myocardial ischaemia from 1.5 +/- 0.4 to 0.8 +/- 0.4 impulses s(-1). Similarly, the polyclonal antibody significantly reduced the discharge frequency of ischaemically sensitive cardiac afferents from 2.5 +/- 0.7 to 1.1 +/- 0.4 impulses s(-1). However, pre-blockade of 5-HT3 receptors eliminated the influence of the antibody on discharge activity of the afferents during ischaemia. This study demonstrates that ROS generated from the oxidation of purines contribute to the stimulation of ischaemically sensitive cardiac sympathetic afferents, whereas PMNs do not play a major role in this process.

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.

Bradykinin receptor antagonists attenuate neointimal proliferation postangioplasty

Bradykinin has been linked to the development of restenosis in response to vascular injury. We therefore examined the effect of bradykinin on vascular smooth muscle cell growth and neointimal formation in organ culture. Bradykinin stimulated both RNA and DNA synthesis (by 175%) in smooth muscle cells from either porcine or human coronary arteries and increased cell number in a concentration-dependent manner. Both p42/44 mitogen-activated protein kinase (MAPK) and p38 kinase were also activated. Treatment with [Hyp(3),Tyr(Me)(8)]bradykinin, a B(2) receptor agonist, stimulated thymidine incorporation by 146%, whereas B(1)-selective Lys-des-Arg(9)-bradykinin had no effect. Addition of the B(2) antagonist HOE-140 reduced the stimulation by 56%, whereas B(1)-selective des-Arg-HOE-140 had no significant effect. Similarly, HOE-140 attenuated angioplasty-induced neointimal formation in organ culture with an efficacy approaching 100% inhibition. These experiments suggest that bradykinin promotes smooth muscle proliferation after vascular injury, presumably via B(2) receptor-dependent activation of MAPK family pathways, and may explain the negative outcome of angiotensin converting enzyme inhibitor therapy on restenosis in nonrodent models.

Cardiac sympathetic afferent activation provoked by myocardial ischemia and reperfusion. Mechanisms and reflexes

Cardiac sympathetic afferents are known to reflexly activate the cardiovascular system, leading to increases in blood pressure, heart rate, and myocardial contractile function. During myocardial ischemia, these sensory nerves also transmit the sensation of pain (angina pectoris) and cause tachyarrhythmias. The authors' laboratory has been interested in defining the mechanisms of activation of this neural system during ischemia and reperfusion. During these periods, reactive oxygen species, particularly hydroxyl radicals, are produced from the breakdown of purine metabolites and lead to stimulation of sympathetic (and vagal) ventricular chemosensitive nerve endings. For example, stimulation with hydrogen peroxide leads to a small reflex increase in blood pressure from the predominant sympathetic afferent activation that is reduced by simultaneous activation of cardiac vagal afferents (known to exert predominantly depressor reflexes). Central integration of these two opposing reflexes likely occurs at several regions of the brain stem, including the nucleus tractus solitarii, where neural occlusion occurs during simultaneous cardiac sympathetic and vagal-afferent stimulation. Activation of platelets also appears to play a role during myocardial ischemia, leading to local release of serotonin (5HT), which, through a 5HT3 mechanism, stimulates sympathetic afferents. Finally, regional changes in pH from lactic acid (but not hypercapnia), stimulate ventricular afferents and may activate kallikrein to increase bradykinin (BK), which, in turn, breaks down arachidonic acid to form prostaglandins. Prostaglandins sensitize cardiac sympathetic afferents to BK. Thus, stimulation of cardiac sympathetic afferents during ischemia and reperfusion and the resulting reflex events form a multifactorial process resulting from activation of a number of chemical pathways in the myocardium.

Transduction capabilities of neonatal ventricular afferent neurons in vivo

We sought to determine the capacity of ventricular sensory nerve endings (neurites) associated with neonatal nodose ganglion afferent neurons to transduce mechanical and chemical stimuli in situ. Spontaneous activity generated by 17 nodose ganglion cardiac afferent neurons was identified in 8 anesthetized neonatal pigs (10-21 days old) using extracellular recording recording techniques. The activity generated by afferent neurons was studied when their ventricular sensory neurites were exposed to local mechanical or chemical stimuli, following systemic administration of specific chemicals or during brief periods of apnea. Gentle mechanical distortion of their ventricular sensory fields enhanced the activity generated by 6 spontaneously active afferent neurons, while suppressing the activity generated by another 3 neurons. Afferent neuronal activity was either enhanced or suppressed when the following chemicals were applied to identified ventricular epicardial sensory fields: the sodium channel modifier veratridine (92% of tested neurons); the P1-purinoceptor agonist adenosine (92%); the neuropeptides angiotensin II (100%), bradykinin (90%) and substance P (90%); and the nitric oxide donor S-nitroso-N-acetylpenicillamine (100%). Epicardial application of isoproternol or nicotine induced modest neuronal responses. Cardiac afferent neurons were also affected when these chemicals were administered systemically. Apnea of 60-100 s duration modified (enhanced, n = 2; suppressed, n = 5) the activity generated by most identified afferent neurons. The estimated average conduction velocity of afferent axons associated with these neurons was 1.0 +/- 0.2 m/s. It is concluded that neonatal nodose ganglion cardiac afferent neurons respond to many of the chemicals known to modify adult cardiac afferent neurons. That cardiac afferent neurons are capable of sensing the mechanical and chemical milieu of the neonatal heart should be taken into account when considering altered neonatal cardiovascular status such as occurs during apnea.

The kallikrein-kininogen-kinin system: lessons from the quantification of endogenous kinins

The purpose of the present review is to describe the place of endogenous kinins, mainly bradykinin (BK) and des-Arg(9)-BK in the kallikrein-kininogen-kinin system, to review and compare the different analytical methods reported for the assessment of endogenous kinins, to explain the difficulties and the pitfalls for their quantifications in biologic samples and finally to see how the results obtained by these methods could complement and extend the pharmacological evidence of their pathophysiological role.

Intrapericardiac injections of algogenic chemicals excite primate C1-C2 spinothalamic tract neurons

Extracellular potentials of 38 C1-C2 spinothalamic tract (STT) neurons in anesthetized monkeys (Macaca fascicularis) were examined for responses to intrapericardiac injections of an algogenic chemical mixture (adenosine, 10(-3) M; bradykinin, prostaglandin E(2), serotonin, histamine, each 10(-5) M). Chemical stimulation of cardiac/pericardiac receptors increased activity of 21 cells, decreased activity of 5 cells, and did not change activity of 12 cells. Cells excited by chemical stimuli received input from noxious mechanical stimulation of somatic fields; most receptive fields included the neck, inferior jaw, or head areas. Nerve ablations in 11 cells excited by intrapericardiac chemicals showed that cardiac input activated by algogenic chemicals traveled primarily in vagal afferent fibers to C1-C2 segments; phrenic or cardiopulmonary sympathetic inputs were predominant in 2 of 11 cells. These results supported the concept that activation of cardiac vagal afferents might lead to the production of referred pain sensation in somatic fields innervated from high cervical segments.

Regulation of the kinin receptors after induction of myocardial infarction: a mini-review

It is well known that the responses to vasoactive kinin peptides are mediated through the activation of two receptors termed bradykinin receptor B1 (B1R) and B2 (B2R). The physiologically prominent B2R subtype has certainly been the subject of more intensive efforts in structure-function studies and physiological investigations. However, the B1R activated by a class of kinin metabolites has emerged as an important subject of investigation within the study of the kallikrein-kinin system (KKS). Its inducible character under stress and tissue injury is therefore a field of major interest. Although the KKS has been associated with cardiovascular regulation since its discovery at the beginning of the last century, less is known about the B1R and B2R regulation in cardiovascular diseases like hypertension, myocardial infarction (MI) and their complications. This mini-review will summarize our findings on B1R and B2R regulation after induction of MI using a rat model. We will develop the hypothesis that differences in the expression of these receptors may be associated with a dual pathway of the KKS in the complex mechanisms of myocardial remodeling.

Myocardial bradykinin B2-receptor expression at different time points after induction of myocardial infarction

OBJECTIVE

To characterize the regulation of the myocardial bradykinin B2 receptor after induction of myocardial infarction (MI), we studied its expression at different time points in the left ventricle (LV), right ventricle (RV) and interventricular septum (S) of the heart.

DESIGN

Male Sprague-Dawley rats were submitted to permanent occlusion of the left descending coronary artery. Six hours, 24 h or 6 days after MI induction or a sham operation, a Millar-tip catheter was placed in the LV. Left ventricular pressure (LVP) and contractility [(dP/dt)max] were measured. The LV, RV and S of all animals were isolated, and total RNA was extracted. B2-receptor expression was analysed by an RNase-protection assay. In addition, Western blot analysis was used to determine protein levels of the B2 receptor in the infarcted area of the LV.

RESULTS

We observed a decrease in LVP and contractility at all time points after MI in comparison with sham-operated animals. Basal B2-receptor expression was detected in the LV and RV, but not in the S of sham-operated rats. In the LV of infarcted hearts, we found a time-dependent up-regulation of the B2-receptor expression, which was increased twofold and fivefold, respectively, 6 h and 24 h after induction of MI compared with controls. This increase was maintained for at least 6 days. Similarly, we also found an up-regulation of the B2-receptor expression in the RV and S. Both reached a peak 24 h after induction of MI. The protein level of the receptor gradually increased up to day 6.

CONCLUSION

We conclude that myocardial ischaemia triggers B2-receptor up-regulation in both the infarcted and non-infarcted areas of the heart.

Upregulation of the cardiac bradykinin B2 receptors after myocardial infarction

An increase in myocardial bradykinin (BK) might be a mechanism to protect the heart during acute myocardial infarction (MI). To characterize the regulation of the myocardial B2 receptor during MI, we studied the expression of this BK receptor in the right ventricle (RV), left ventricle (LV) and myocardial septum (S) 24 h after left coronary ligation. Experiments were performed in male Wistar Kyoto rats (n = 10) and compared with sham operated animals (n = 6). After total RNA extraction, the myocardial B2-receptor expression was analyzed by a RNase protection assay (n = 6), using a specific probe from the coding region of the receptor gene. After 24 h, rats with MI were normotensive and showed an impaired left ventricular function. The B2-receptor expression of the LV of these rats was significantly elevated (2.3-fold) compared to sham operated rats. Furthermore, we found a dramatic upregulation of the B2 receptor in the RV (7.8-fold) and a dramatic expression of B2 receptor mRNA in S of infarcted hearts, whereas in the S of sham operated rats no B2 receptor expression could be detected. Our data show clearly that the described increase in BK during myocardial ischemia is accompanied by an elevated B2-receptor expression in the infarcted and non-infarcted parts of cardiac ventricles.

Intrarenal infusion of bradykinin elicits a pressor response in conscious rats via a B2-receptor mechanism

Bradykinin (BK) is a peptide known to activate afferent nerve fibers from the kidney and elicit reflex changes in the cardiovascular system. The present study was specifically designed to test the hypothesis that bradykinin B2 receptors mediated the pressor responses elicited during intrarenal bradykinin administration. Pulsed Doppler flow probes were positioned around the left renal artery to measure renal blood flow (RBF). A catheter, to permit selective intrarenal administration of BK, was advanced into the proximal left renal artery. The femoral artery was cannulated to measure mean arterial pressure (MAP). MAP, heart rate (HR), and RBF were recorded from conscious unrestrained rats while five-point cumulative dose-response curves during an intrarenal infusion of BK (5-80 µg·kg-1·min-1) were constructed. Intrarenal infusion of BK elicited dose-dependent increases in MAP (maximum pressor response, 26 ± 3 mmHg), accompanied by a significant tachycardia (130 ± 18 beats/min) and a 28% increase in RBF. Ganglionic blockade abolished the BK-induced increases in MAP (maximum response, -6 ± 5 mmHg), HR (maximum response 31 ± 14 beats/min), and RBF (maximum response, 7 ± 2%). Selective intrarenal B2-receptor blockade with HOE-140 (50 µg/kg intrarenal bolus) abolished the increases in MAP and HR observed during intrarenal infusion of BK (maximum MAP response, -2 ± 3 mmHg; maximum HR response, 15 ± 11 beats/min). Similarly, the increases in RBF were prevented after HOE-140 treatment. In fact, after HOE-140, intrarenal BK produced a significant decrease in RBF (22%) at the highest dose of BK. Results from this study show that the cardiovascular responses elicited by intrarenal BK are mediated predominantly via a B2-receptor mechanism.Key words: bradykinin, blood pressure, renal hemodynamics, B2 receptors, autonomic nervous system.

Role of protons in activation of cardiac sympathetic C-fibre afferents during ischaemia in cats

1. Chest pain caused by myocardial ischaemia is mediated by cardiac sympathetic afferents. The mechanisms of activation of cardiac afferents during ischaemia remain poorly understood. Increased lactic acid production is associated closely with myocardial ischaemia. The present study examined the role of protons generated during ischaemia in activation of cardiac sympathetic C-fibre afferents. 2. Single-unit activity of cardiac afferents innervating both ventricles was recorded from the left sympathetic chain in anaesthetized cats. Epicardial tissue pH was measured within 1-1.5 mm of the surface by a pH-sensitive needle electrode. Responses of cardiac afferents to myocardial ischaemia, lactic acid, sodium lactate, acidic phosphate buffer and hypercapnia were determined. 3. Occlusion of the coronary artery for 5 min decreased epicardial tissue pH from 7.35 +/- 0.21 to 6.98 +/- 0.22 (P < 0.05). Epicardial placement of isotonic neutral phosphate buffer, but not saline, prevented the ischaemia-induced decrease in epicardial pH. This manoeuvre significantly attenuated the response of 16 afferents to 5 min of ischaemia (1.56 +/- 0.23 pre-treatment vs. 0.67 +/- 0.18 impulses s-1). Topical application of 10-100 microg ml-1 of lactic acid, but not sodium lactate, concentration-dependently stimulated 18 cardiac afferents. Inhalation with high-CO2 gas failed to activate 12 separate cardiac afferents. Furthermore, lactic acid stimulated cardiac afferents to a greater extent than acidic phosphate buffer solution, applied at a similar pH to the same afferents. 4. Collectively, this study provides important in vivo evidence that protons contribute to activation/sensitization of cardiac sympathetic C-fibre afferents during myocardial ischaemia.

Effect of acetylsalicylate on cardiac and muscular pain induced by intracoronary and intra-arterial infusion of bradykinin in humans

OBJECTIVES

This study assessed the algesic activity of bradykinin (BK) in humans and the effects of acetylsalicylate on muscular and cardiac BK-induced pain.

BACKGROUND

Bradykinin is released by the ischemic myocardium and may be involved in the genesis of ischemic pain.

METHODS

Increasing doses of BK (from 30 to 960 ng/min) were randomly infused, for periods of 2 min each, into the iliac artery of 10 patients. The same protocol was repeated 30 min after the IV administration of 1 g of acetylsalicylate. In eight other patients with coronary artery disease, the same increasing doses of BK, for periods of 2 min each, were infused into the left coronary artery. The same protocol was repeated 30 min after the IV administration of 1 g of acetylsalicylate. Time to pain onset and maximal pain severity were obtained.

RESULTS

Before acetylsalicylate administration, all patients experienced pain during intra-iliac infusion of BK. After acetylsalicylate, eight patients did not experience any pain during BK infusion (p = 0.0014), and in the two remaining patients, time to pain onset and maximal pain severity were similar to those recorded before acetylsalicylate. Before acetylsalicylate administration, all patients experienced pain similar to their habitual angina during intracoronary BK infusion. After acetylsalicylate, six patients did not experience any pain during BK infusion (p = 0.0098), whereas in the two remaining patients time to pain onset and maximal pain severity were similar to those recorded before acetylsalicylate.

CONCLUSIONS

Intra-iliac infusion of BK causes muscular pain, and its intracoronary infusion in patients with coronary artery disease causes cardiac pain, which is similar to their habitual angina. The BK-induced pain is abolished or reduced by acetylsalicylate, thus suggesting that acetylsalicylate-sensitive mediators, such as prostaglandins, are involved in its pathogenesis.

Pharmacology and cardiovascular implications of the kinin-kallikrein system

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

Correlation of ventricular mechanosensory neurite activity with myocardial sensory field deformation

The mechanosensory activity generated by ventricular epicardial sensory neurites associated with afferent axons in thoracic sympathetic nerves was correlated with sensory field deformation (long axis, short axis, and transmural dimension changes), regional intramyocardial pressure, and ventricular chamber pressure in anesthetized dogs. Ventricular mechanosensory neurites generated activity that correlated best with strain developed along either the long or short axis of their epicardial sensory fields in most instances. Activity did not correlate normally to local wall thickness or to regional wall or chamber pressure development in most cases. During premature ventricular contractions, the activity generated by these sensory neurites correlated best with maximum strain developed along at least one sensory field epicardial vector. Identified sensory neurites were also activated by local application of the chemical bradykinin (10 microM) or by local ischemia. These data indicate that the activity generated by most ischemia-sensitive ventricular epicardial sensory neurites associated with afferent axons in sympathetic nerves is dependent on not only their local chemical milieu but on local mechanical deformation along at least one epicardial vector of their sensory fields.

Mechanisms of cardiac pain

Angina pectoris often results from ischemic episodes that excite chemosensitive and mechanoreceptive receptors in the heart. Ischemic episodes release a collage of chemicals, including adenosine and bradykinin, that excites the receptors of the sympathetic and vagal afferent pathways. Sympathetic afferent fibers from the heart enter the upper thoracic spinal cord and synapse on cells of origin of ascending pathways. This review focuses on the spinothalamic tract, but other pathways are excited as well. Excitation of spinothalamic tract cells in the upper thoracic and lower cervical segments, except C7 and C8 segments, contributes to the anginal pain experienced in the chest and arm. Cardiac vagal afferent fibers synapse in the nucleus tractus solitarius of the medulla and then descend to excite upper cervical spinothalamic tract cells. This innervation contributes to the anginal pain experienced in the neck and jaw. The spinothalamic tract projects to the medial and lateral thalamus and, based on positron emission tomography studies, activates several cortical areas, including the anterior cingulate gyrus (BA 24 and 25), the lateral basal frontal cortex, and the mesiofrontal cortex.

Bradykinin B2-receptor-mediated positive chronotropic effect of bradykinin in isolated rat atria

The positive chronotropic effect of bradykinin was investigated in isolated spontaneously beating atria of the rat. Cumulative additions of bradykinin (0.3-100 nM) caused a concentration-dependent increase in the beating rate of the atria by maximally 35+/-4 beats/min, approximately 25% of the 1 microM isoprenaline-induced maximal responses. In contrast, the active metabolite of bradykinin and selective bradykinin B1-receptor agonist, Des-Arg9-bradykinin, did not influence the spontaneous frequency of beating. Propranolol (1 microM) combined with prazosin (1 microM) did not affect the positive chronotropic effect of bradykinin. A selective bradykinin B2-receptor antagonist, Hoe 140, concentration-dependently shifted the response curves for bradykinin to the right, whereas the bradykinin B1-receptor antagonist, Lys-[Leu8]Des-Arg9-bradykinin had no effect. The tachycardic responses to bradykinin were potentiated by ramipril, an angiotensin-converting enzyme/kininase II inhibitor, but not affected by Nomega-nitro-L-arginine methyl ester hydrochloride, a nitric oxide synthesis inhibitor. Indomethacin and meclofenamate, two cyclooxygenase inhibitors, abolished the bradykinin-induced chronotropic effect. These results indicate that exogenous bradykinin induces a positive chronotropic effect that occurs independent of adrenoceptors. The bradykinin-induced chronotropic effect is mediated by bradykinin B2 receptors, whereas B1 receptors do not play a role in mediating this effect. Prostaglandins but not nitric oxide appear to be involved in bradykinin-induced positive chronotropic effect.

The role of bradykinin in the regulation of blood flow to hindlimb muscle groups of the anaesthetized cat

1. Male cats were anaesthetized with alphaxalone-alphadolone and breathed spontaneously following tracheotomy, Using coloured microspheres, muscle blood flow was measured at rest and during two periods of contraction elicited by simultaneous stimulation of the left sciatic and femoral nerves at 3 Hz for 10 min. In one group, the hindlimb blood flow was allowed to increase during muscle contraction and in another group the perfusion of the hindlimb was limited by a stenosis on the left external iliac artery. 2. In the absence of flow restriction, soleus muscle blood flow increased from 18.9 +/- 3.8 to 30.4 +/- 3.3 ml min-1 (100 g tissue)-1 (n = 6; P < 0.02) and gastrocnemius muscle blood flow increased from 24.8 +/- 5.9 to 61.6 +/- 12.8 ml min-1 (100 g tissue)-1 (n = 6; P < 0.01) during contraction. The bradykinin (BK) antagonists HOE 140 (1 mg kg-1, i.v.) did not affect the response in either the soleus (37.7 +/- 7.3 ml min-1 (100 g tissue)-1; n = 6; n.s.) or the gastrocnemius (62.9 +/- 7.9 ml min-1 (100 g tissue)-1; n = 6; n.s.) muscles. 3. In the stenosis group, soleus muscle blood flow increased from 9.8 +/- 2.3 to 22.9 +/- 4.9 ml min-1 (100 g tissue)-1 (n = 6; P < 0.01) and gastrocnemius muscle blood flow increased from 15.8 +/ 3.4 to 36.4 +/- 5.5 ml min-1 (100 g tissue)-1 (n = 6; P < 0.01) during contraction. Following administration of HOE 140, functional hyperaemia in the soleus muscle was unaffected (blood flow, 17.8 +/- 2.2 ml min-1 (100 g tissue)-1, n = 6; n.s.) white blood flow in the gastrocnemius muscle was reduced to 21.8 +/- 6.0 ml min-1 (100 g tissue)-1 (n = 6; P < 0.05). 4. The results show that BK does not contribute ot functional hyperaemia associated with twitch contraction at 3 Hz when blood flow is unrestricted, but may contribute up to 40% of the vasodilation of predominantly glycolytic muscle groups such as the gastrocnemius when flow is restricted. BK plays no role in hyperaemia associated with twitch contraction of oxidative muscle groups such as the soleus.

Endogenous bradykinin activates ischaemically sensitive cardiac visceral afferents through kinin B2 receptors in cats

1. Activity of ischaemically sensitive cardiac visceral afferents during myocardial ischaemia induces both angina and cardiovascular reflexes. Increased production of bradykinin (BK) and cyclo-oxygenase products (i.e. prostaglandins (PGs)) occurs during myocardial ischaemia. However, the role of these agents in activation of ischaemically sensitive cardiac afferents has not been established. The present study tested the hypothesis that BK produced during ischaemia activates cardiac afferents through kinin B2 receptors. 2. Single-unit activity of cardiac afferents innervating the left ventricle was recorded from the left thoracic sympathetic chain (T1-T4) of anaesthetized cats. Ischaemically sensitive cardiac afferents were identified according to their response to 5 min of myocardial ischaemia. The mechanism of BK in activation of ischaemically sensitive cardiac afferents was determined by injection of BK (1 microgram kg-1 i.a.), des-Arg9-BK (1 microgram kg-1 i.a., a specific kinin B1 receptor agonist), kinin B2 receptor antagonists: HOE140 (30 micrograms kg-1 i.v.) and NPC-17731 (40 micrograms kg-1 i.v., cyclo-oxygenase inhibition with indomethacin (5 mg kg-1 i.v.) and NPC-17731 (40 micrograms kg-1 i.v.) after pretreatment with indomethacin (5 mg kg-1 i.v.). 3. We observed that BK increased the discharge rate of all eleven ischaemically sensitive cardiac afferents from 0.39 +/- 0.12 to 1.47 +/- 0.37 impulses s-1 (P < 0.05). Conversely, des-Arg9-BK did not significantly increase the activity of eleven ischaemically sensitive fibres (0.58 +/- 0.02 vs. 0.50 +/- 0.18 impulses s-1. HOE140 significantly attenuated the response of twelve afferents to ischaemia (0.61 +/- 0.22 to 1.85 +/- 0.5 vs. 0.53 +/- 0.16 to 1.09 +/- 0.4 impulses s-1). NPC-17731, another kinin B2 receptor antagonist, had similar inhibitory effects on six other ischaemically sensitive cardiac afferents (0.35 +/- 0.14 to 1.19 +/- 0.29 vs. 0.22 +/- 0.08 to 0.23 +/- 0.07 impulses s-1). Indomethacin significantly reduced the responses of seven afferents to ischaemia (0.35 +/- 0.13 to 1.89 +/- 0.48 vs. 0.40 +/- 0.10 to 0.76 +/- 0.24 impulses s-1). Indomethacin also significantly reduced the responses of six ischaemically sensitive cardiac afferents to BK (2.65 +/ 1.23 to 1.2 +/- 0.51 impulses s-1. In six cats pretreated with indomethacin, NPC-17731 attenuated the impulse activity of six ischaemically sensitive cardiac afferents (0.39 +/- 0.12 to 1.0 +/- 0.3 vs. 0.26 +/- 0.14 to 0.48 +/- 0.20 impulses s-1. 4. This study demonstrates that BK produced during ischaemia contributes to stimulation of ischaemically sensitive cardiac visceral afferents through activation of kinin B2 receptors. Furthermore, BK stimulates ischaemically sensitive cardiac visceral afferents through a mechanism that is, at least in part, independent of cyclo-oxygenase activation.

Importance of neurokinin-1 receptors in the nucleus tractus solitarii of mice for the integration of cardiac vagal inputs

Unmyelinated vagal afferents from the heart terminate within the nucleus tractus solitarii (NTS) located in the dorsomedial medulla. The neurotransmitter and postsynaptic receptors mediating information from cardiac vagal receptors to the NTS are unknown. This study determined the effects of neurokinin-1 (NK1) receptor blockade on: (i) the reflex response evoked following aortic root injection of either veratridine (1-3 microg/kg) or bradykinin (80-300 ng/kg) to stimulate cardiac receptors in in vivo anaesthetized mice; and (ii) the evoked synaptic response of cardioreceptive NTS neurons following both intraleft-ventricular injection of veratridine or bradykinin, and electrical stimulation of the ipsilateral vagus nerve in an arterially perfused working heart-brainstem preparation of mouse. Administration of CP-99,994 (0.75-1.5 mg/kg i.v.), a specific NK1 antagonist, attenuated significantly the evoked reflex bradycardia and depressor response following cardiac receptor (n = 6), but not pulmonary chemoreflex stimulation in vivo. From extracellular recordings of cardioreceptive NTS neurons, CP-99,994 reduced reversibly the total number of evoked spikes, peak firing frequency and response duration evoked by intraventricular injections of veratridine (n = 5) or bradykinin (n = 5). The number of evoked action potentials following electrical stimulation of the vagus nerve was also reduced. In five whole cell recordings of NTS neurons, both the evoked depolarization following cardiac receptor stimulation, and the peak amplitude and duration of vagus nerve-evoked EPSPs were reduced by CP-99,994; synaptic inputs from both peripheral chemoreceptors or pulmonary C-fibres were unaffected. These data support a selective involvement of NK1 receptors in the transmission of cardiac vagal afferent inputs to NTS neurons integrating cardiorespiratory information.

Thoracic spinal neuron responses to repeated myocardial ischemia and epicardial bradykinin

Bradykinin has been strongly implicated as a mediator of cardiac nociception. During coronary artery occlusion, the content of bradykinin in coronary sinus blood increases. In non-cardiac tissues nociception to bradykinin exhibits tachyphylaxis, however, this phenomenon has not been rigorously studied in the heart. This raises the question that repeated coronary occlusions may also result in tachyphylaxis, thereby reducing cardiac sensation on subsequent ischemic stimulation. We therefore examined the hypothesis that repetitive episodes of myocardial ischemia and of epicardial application of bradykinin demonstrate tachyphylaxis. Mongrel cats were anesthetized with alpha-chloralose and heart rate, arterial pressure, and thoracic spinal neuron firing rate were recorded during 60 s of anterior descending coronary occlusion or local epicardial application of bradykinin (10 microM). Neurons were identified by cutaneous receptive fields in the left shoulder area. Sixty-one of 93 neurons tested responded with an increase in firing rate to coronary artery occlusion only (n=24), bradykinin only (n=19) or to both (n=18). On repetitive coronary occlusion, 14 of 25 neurons demonstrated tachyphylaxis compared to 12 of 15 tested with bradykinin (p<0.05). Similar responses were observed in thoracic spinal neurons that projected to the brain. In neurons demonstrating tachyphylaxis, dorsal cervical cold block partially restored the neuronal activation to coronary occlusion but not to bradykinin. We conclude, based on neuronal responses to repetitive stimuli, that afferent spinal responses to coronary occlusion and bradykinin are different. These data suggest that bradykinin is not the sole mediator of myocardial ischemic pain. The tachyphylaxis to repeated coronary artery occlusions may contribute to the clinical phenomenon of silent myocardial ischemia.

Positive chronotropic activity of bradykinin in the pithed normotensive rat

The positive chronotropic effect of bradykinin was investigated in the pithed rat preparation. Cumulative treatment with bradykinin (0.20 nmol/kg-6.59 mumol/kg, intravenous [i.v.]) caused a dose-dependent increase in heart rate (HR) by a maximum of 80 +/- 3.3 beats min-1. In contrast, the active metabolite of bradykinin and selective bradykinin B1-receptor agonist, [des-Arg9]-bradykinin did not influence the spontaneous frequency of beating. Propranolol alone reduced the bradykinin-induced increase in HR and a combination of propranolol with prazosin abolished the chronotropic effect of bradykinin. The selective bradykinin B2 receptor antagonist. Hoe 140, dose-dependently shifted the dose-response curves of bradykinin to the right, whereas the bradykinin B1 receptor antagonist, des-Arg10-[Leu9]-kallidin proved ineffective. From our experiments it may be concluded that bradykinin induces tachycardia in the pithed rat primarily by stimulating the sympathetic ganglia leading to the release of noradrenaline, which subsequently activates cardiac beta 1-adrenoceptors. The bradykinin-induced chronotropic effect is mediated by bradykinin B2-receptors, whereas B1-receptors appear not to be involved.

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.