Ventricular arrhythmias parallel cardiac histamine efflux after coronary artery occlusion in the dog

The Roles of Cardiovascular H2-Histamine Receptors Under Normal and Pathophysiological Conditions

This review addresses pharmacological, structural and functional relationships among H₂-histamine receptors and H₁-histamine receptors in the mammalian heart. The role of both receptors in the regulation of force and rhythm, including their electrophysiological effects on the mammalian heart, will then be discussed in context. The potential clinical role of cardiac H₂-histamine-receptors in cardiac diseases will be examined. The use of H₂-histamine receptor agonists to acutely increase the force of contraction will be discussed. Special attention will be paid to the potential role of cardiac H₂-histamine receptors in the genesis of cardiac arrhythmias. Moreover, novel findings on the putative role of H₂-histamine receptor antagonists in treating chronic heart failure in animal models and patients will be reviewed. Some limitations in our biochemical understanding of the cardiac role of H₂-histamine receptors will be discussed. Recommendations for further basic and translational research on cardiac H₂-histamine receptors will be offered. We will speculate whether new knowledge might lead to novel roles of H₂-histamine receptors in cardiac disease and whether cardiomyocyte specific H₂-histamine receptor agonists and antagonists should be developed.

Characterization of Stressed Transgenic Mice Overexpressing H2-Histamine Receptors in the Heart

We studied transgenic mice with cardiac-specific overexpression of H2-histamine receptors (H2-TG) by using the α-myosin heavy-chain promoter. We wanted to address whether this overexpression would protect the heart against paradigmatic stressors. To this end, we studied isolated atrial preparations in an organ bath under normoxic and hypoxic conditions and after prolonged exposure to high histamine concentrations. Moreover, we assessed cardiac function using echocardiography in mice with cardiac hypertrophy due to overexpression of the catalytic subunit of PP2A (PP2A-TG) in the heart [H2-TG × PP2A-TG = double transgenic (DT)] or H2-TG with cardiac systolic failure due to treatment of mice with lipopolysaccharides (LPSs). Furthermore, the effect of ischemia and reperfusion was studied in isolated perfused hearts (Langendorff mode) of H2-TG. We detected evidence for the protective role of the overexpressed H2-histamine receptors in the contractile dysfunction of DT and isolated atrial preparations subjected to hypoxia. In contrast, we noted the detrimental role of H2-histamine receptor overexpression against ischemia (Langendorff perfusion) and LPS-induced systolic heart failure. Hence, the role of H2-histamine receptors in the heart is context-sensitive: the results differ between hypoxia (in atrium) and ischemia (perfused whole heart), as well as between genetically induced hypertrophy (DT) and toxin-induced heart failure (LPS). The underlying molecular mechanisms for the protective or detrimental roles of H2-histamine receptor overexpression in the mammalian heart remain to be elucidated. SIGNIFICANCE STATEMENT: The beneficial and detrimental effects of the cardiac effects of H2-histamine receptors in the heart under stressful conditions, here intended to mimic clinical situations, were studied. The data suggest that depending on the clinically underlying cardiac pathophysiological mechanisms, H2-histamine agonists or H2-histamine antagonists might merit further research efforts to improve clinical drug therapy.

Accelerated cardiomyocyte senescence contributes to late-onset doxorubicin-induced cardiotoxicity

Children surviving cancer and chemotherapy are at risk for adverse health events including heart failure that may be delayed by years. Although the early effects of doxorubicin-induced cardiotoxicity may be attributed to a direct effect on the cardiomyocytes, the mechanisms underlying the delayed or late effects (8-20 yr) are unknown. The goal of this project was to develop a model of late-onset doxorubicin-induced cardiotoxicity to better delineate the underlying pathophysiology responsible. The underlying hypothesis was that doxorubicin-induced "late-onset cardiotoxicity" was the result of mitochondrial dysfunction leading to cell failure and death. Wistar rats, 3-4 wk of age, were randomly assigned to vehicle or doxorubicin injection groups (1-45 mg/kg). Cardiovascular function was unaltered at the lower dosages (1-15 kg/mg), but beginning at 6 mo after injection significant cardiac degradation was observed in the 45 mg/kg group. Doxorubicin significantly increased myocardial mitochondrial DNA (mtDNA) damage. In contrast, in isolated c-kit left ventricular (LV) cells, doxorubicin treatment did not increase mtDNA damage. Biomarkers of senescence within the LV were significantly increased, suggesting accelerated aging of the LV. Doxorubicin also significantly increased LV histamine content suggestive of mast cell activation. With the use of flow cytometry, a significant expansion of the c-kit and stage-specific embryonic antigen 1 cell populations within the LV were concomitant with significant decreases in the circulating peripheral blood population of these cells. These results are consistent with the concept that doxorubicin induced significant damage to the cardiomyocyte population and that although the heart attempted to compensate it eventually succumbed to an inability for self-repair.

Histamine deficiency exacerbates myocardial injury in acute myocardial infarction through impaired macrophage infiltration and increased cardiomyocyte apoptosis

Histamine is a biogenic amine that is widely distributed and has multiple functions, but the role it plays in acute myocardial infarction (AMI) remains unclear. In this study, we investigated the origin and contribution of endogenous histamine to AMI. Histidine decarboxylase (HDC) is the unique enzyme responsible for histamine generation. Using HDC-EGFP bacterial artificial chromosome (BAC) transgenic mice in which EGFP expression is controlled by the HDC promoter, we identified HDC expression primarily in CD11b(+)Gr-1(+) immature myeloid cells (IMCs) that markedly increase in the early stages of AMI. Deficiency of histamine in HDC knockout mice (HDC(-/-)) reduced cardiac function and exacerbated the injury of infarcted heart. Furthermore, administering either an H1 receptor antagonist (pyrilamine) or an H2 receptor antagonist (cimetidine) demonstrated a protective effect of histamine against myocardial injury. The results of in vivo and in vitro assays showed that histamine deficiency promotes the apoptosis of cardiomyocytes and inhibits macrophage infiltration. In conclusion, CD11b(+)Gr-1(+) IMCs are the predominant HDC-expressing sites in AMI, and histamine plays a protective role in the process of AMI through inhibition of cardiomyocyte apoptosis and facilitation of macrophage infiltration.

The impact of mast cells on cardiovascular diseases

Mast cells comprise an innate immune cell population, which accumulates in tissues proximal to the outside environment and, upon activation, augments the progression of immunological reactions through the release and diffusion of either pre-formed or newly generated mediators. The released products of mast cells include histamine, proteases, as well as a variety of cytokines, chemokines and growth factors, which act on the surrounding microenvironment thereby shaping the immune responses triggered in various diseased states. Mast cells have also been detected in the arterial wall and are implicated in the onset and progression of numerous cardiovascular diseases. Notably, modulation of distinct mast cell actions using genetic and pharmacological approaches highlights the crucial role of this cell type in cardiovascular syndromes. The acquired evidence renders mast cells and their mediators as potential prognostic markers and therapeutic targets in a broad spectrum of pathophysiological conditions related to cardiovascular diseases.

Glucagon effects on 3H-histamine uptake by the isolated guinea-pig heart during anaphylaxis

We estimated the influence of acute glucagon applications on ³H-histamine uptake by the isolated guinea-pig heart, during a single ³H-histamine passage through the coronary circulation, before and during anaphylaxis, and the influence of glucagon on level of histamine, NO, O₂⁻, and H₂O₂ in the venous effluent during anaphylaxis. Before anaphylaxis, glucagon pretreatment does not change ³H-histamine Umax and the level of endogenous histamine. At the same time, in the presence of glucagon, ³H-histamine Unet is increased and backflux is decreased when compared to the corresponding values in the absence of glucagon. During anaphylaxis, in the presence of glucagon, the values of ³H-histamine Umax and Unet are significantly higher and backflux is significantly lower in the presence of glucagon when compared to the corresponding values in the absence of glucagon. The level of endogenous histamine during anaphylaxis in the presence of glucagon (6.9–7.38 × 10⁻⁸  μM) is significantly lower than the histamine level in the absence of glucagon (10.35–10.45 × 10⁻⁸  μM). Glucagon pretreatment leads to a significant increase in NO release (5.69 nmol/mL) in comparison with the period before glucagon administration (2.49 nmol/mL). Then, in the presence of glucagon, O₂⁻ level fails to increase during anaphylaxis. Also, our results show no significant differences in H₂O₂ levels before, during, and after anaphylaxis in the presence of glucagon, but these values are significantly lower than the corresponding values in the absence of glucagon. In conclusion, our results show that glucagon increases NO release and prevents the increased release of free radicals during anaphylaxis, and decreases histamine level in the venous effluent during cardiac anaphylaxis, which may be a consequence of decreased histamine release and/or intensified histamine capturing by the heart during anaphylaxis.

Histamine: metabolism, physiology, and pathophysiology with applications in veterinary medicine

OBJECTIVE

To review the human and veterinary literature on histamine physiology and pathophysiology and potential applications for clinical use in veterinary critical care.

DATA SOURCES

Human and veterinary clinical studies, reviews, texts, and recent research in histamine receptor and antagonist therapy.

HUMAN DATA SYNTHESIS

Recent progress in molecular biology has led to a more complete understanding of the enzymes involved in histamine metabolism and histamine receptor physiology. The past decade of research has confirmed the role of histamine in the classical functions (contraction of smooth muscle, increase in vascular permeability, and stimulation of gastric acid secretion) and has also elucidated newer ones that are now under investigation. Data on the roles of histamine in angiogenesis, circadian rhythm, bone marrow regeneration, bacterial eradication, and cancer are emerging in the literature. Newer histamine antagonists are currently in drug trials and are expected to advance the clinical field in treatment of allergic, gastrointestinal, and cognitive disorders.

VETERINARY DATA SYNTHESIS

Veterinary histamine research is directed at identifying the effects of certain pharmacological agents on blood histamine concentrations and establishing the relevance in clinical disease states. Research demonstrates important species differences in regards to histamine receptor physiology and tissue response. Studies in the area of trauma, sepsis, anaphylaxis, allergy, and gastrointestinal disorders have direct applications to clinical veterinary medicine.

CONCLUSIONS

Histamine plays a key role in the morbidity and mortality associated with allergy, asthma, gastric ulcers, anaphylaxis, sepsis, hemorrhagic shock, anesthesia, surgery, cardiovascular disease, cancer, CNS disorders, and immune-mediated disease. Histamine antagonism has been in common use to block its adverse effects. With recent advances in the understanding of histamine receptor physiology, pharmaceutical agents targeting these receptors have increased the therapeutic options.

Mast cell degranulation--a mechanism for the anti-arrhythmic effect of endothelin-1?

BACKGROUND AND PURPOSE

The aim of this study was to investigate whether the previously reported anti-arrhythmic effect of endothelin-1 (ET-1) is mediated by degranulation of cardiac mast cells prior to myocardial ischaemia.

EXPERIMENTAL APPROACH

Male Sprague-Dawley rats received either ET-1 (1.6 nmolxkg(-1)) in the presence or absence of disodium cromoglycate (DSCG; 20 mgxkg(-1)xh(-1)) prior to coronary artery occlusion (CAO). In separate experiments rats were given compound 48/80 (50 microgxkg(-1)) to compare the effects of ET-1 with those of a known mast cell degranulator. Ischaemia-induced ventricular arrhythmias were detected through continuous monitoring of a lead I electrocardiogram. After 30 min of CAO, the hearts were removed and mast cell degranulation determined by histological analysis. A parallel series of sham groups were performed to determine the direct effects of ET-1 and compound 48/80 on mast cell degranulation in the absence of ischaemia.

KEY RESULTS

ET-1 and compound 48/80 both exerted profound anti-arrhythmic effects, significantly reducing the total number of ventricular ectopic beats (P < 0.001) and the incidence of ventricular fibrillation (P < 0.05). These anti-arrhythmic effects were abolished by concomitant DSCG infusion prior to CAO. In sham animals ET-1 and compound 48/80 both induced mast cell degranulation (P < 0.001), an effect which was abolished by DSCG, confirming their ability to induce degranulation of mast cells.

CONCLUSIONS AND IMPLICATIONS

These results demonstrate for the first time that when given prior to ischaemia ET-1 mediates its anti-arrhythmic effects, at least in part, via cardiac mast cell degranulation.

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.

Histamine in Macaca mulatto monkey cardiac sympathetic nerve system: a morphological and functional assessment

Our previous study demonstrated the co-localization of histamine with norepinephrine (NE) within superior cervical ganglia (SCG), and the release of histamine from sympathetic nerve endings of guinea pig evoked by stimulations. We have now further investigated that whether the histamine can be synthesized, stored and released from the sympathetic nerve systems of Macaca mulatto monkey, and investigated the modulation of the sympathetic endogenous histamine release through histamine H(3) receptor in the monkey cardiac sympathetic nerve system. Double-labeled immunofluorescence technique was applied to investigate co-localization of histamine and NE in SCG of Macaca mulatto monkey. The cardiac sympathetic nerve terminals (synaptosomes) of Macaca mulatto monkey was prepared and depolarized with 50 mmol/L K(+). Histamine released from synaptosomes was detected by spectrofluorometer and regulations of histamine release through Ca(2+), Ca(2+)-channel blockers, H(3)-receptor agonist (R)-alpha-methylhistamine and histamine H(3)-receptor antagonist, thioperamide were observed. Co-localization of histamine and NE was identified within the same neuron of SCG. Release of histamine was Ca(2+)-dependent and inhibited by N-type Ca(2+)-channel blocker omega-conotoxin, but not affected by the L-type Ca(2+)-channel blocker lacidipine. Compound 48/80, a mast cell releaser, did not affect cardiac synaptosome histamine exocytosis. Cardiac synaptosome histamine release was augmented by the enhanced synthesis of histamine or the inhibition of histamine metabolism. Histamine H(3)-receptor activation by (R)-alpha-methylhistamine inhibited high K(+)-evoked histamine release and thioperamide blocked the effects of (R)-alpha-methylhistamine. These results firstly showed that histamine co-existed with NE within sympathetic neurons of monkey and the exocytosis of histamine from sympathetic terminals could be regulated by presynaptic histamine H(3) receptors. Sympathetic histamine may act as a neurotransmitter to modulate sympathetic neurotransmission.

Histamine Contributes to Ischemia-Related Activation of Cardiac Spinal Afferents: Role of H1 Receptors and PKC

Myocardial ischemia activates cardiac spinal afferents that transmit the nociceptive information leading to chest pain and elicit excitatory cardiovascular reflexes. Previous studies have shown that histamine is increased in coronary sinus blood during myocardial ischemia and that this autacoid stimulates abdominal visceral afferents. The present investigation evaluated the role of endogenous histamine in stimulation of ischemically sensitive cardiac spinal afferents. Nerve activity of single-unit cardiac afferents was recorded from the left sympathetic chain or rami communicans (T2–T5) in anesthetized cats. Sixty-four cardiac afferents were identified. Injection (5–30 μg/kg) of histamine into the left atrium (LA) stimulated 7 ischemically sensitive cardiac afferents resulting in a significant increase in their activity in a dose-dependent manner. Also, LA injection of histamine (10 μg/kg) stimulated 7 of 8 ischemically insensitive cardiac spinal afferents. Administrations of 2-(3-chlorophenyl)histamine (250 μg/kg, LA), a specific H1 receptor agonist and histamine (10 μg/kg, LA), stimulated 9 other ischemically sensitive cardiac afferents (0.48 ± 0.10 to 1.40 ± 0.20 imp/s). In contrast, dimaprit (500 μg/kg, LA), an H2 receptor agonist, stimulated only one of the 9 afferents and thus did not alter their overall activity (0.40 ± 0.09 to 0.54 ± 0.09 imp/s). ( R)α-Methyl-histamine (500 μg/kg, LA), an H3 receptor agonist, did not stimulate any of the 9 afferents. Pyrilamine (300 μg/kg, iv), a selective H1 receptor antagonist, attenuated the activity of 8 afferents during 5 min of ischemia from 3.32 ± 0.38 to 1.87 ± 0.28 imp/s and abolished the response of 9 other cardiac afferents to histamine. Finally, administration of PKC-(19–36) (30 μg/kg, iv), a selective inhibitor of protein kinase C, attenuated the response of 8 cardiac afferents to histamine by 32%. These data indicate that endogenous histamine contributes to activation of cardiac sympathetic afferents during myocardial ischemia through H1 receptors and that the action of histamine on these cardiac afferents is partially dependent on the intracellular PKC pathway.

The effect of histamine receptor antagonists on stress-induced catecholamine secretion: an adrenomedullary microdialysis study in the rat

The effects of pretreatment with selective histamine receptor antagonists on changes in sympathoadrenal activity and haemodynamics, induced by 60-min immobilization stress, were studied in conscious rats. Using adrenomedullary microdialysis, it was shown that ranitidine (5 mg/kg, i.v.), a histamine H2 receptor antagonist, selectively suppressed stress-stimulated noradrenaline secretion without affecting adrenaline response, whereas triprolidine (10 mg/kg, i.v.), a histamine H1 receptor antagonist, had little effect on stress-induced secretion of both catecholamines. Neither triprolidine nor ranitidine changed the pressor response to 60-min stress. The stress-induced increase in heart rate was not altered by triprolidine, whereas ranitidine reduced it after 30 min of stress. To test whether the anti-secretory effect of ranitidine could be of peripheral origin, in a separate experimental series, a local catecholamine secretion was stimulated by histamine (0.5 mM) perfused through the adrenomedullary dialysis probe. It appeared that triprolidine, but not ranitidine, reduced this effect of histamine. Thus, the present results suggest that during stress, the activity of the central histaminergic system, via histamine H2-receptors, may selectively modulate noradrenaline secretion by the adrenal gland.

Endogenous histamine stimulates ischemically sensitive abdominal visceral afferents through H1 receptors

Abdominal ischemia stimulates sympathetic visceral afferents to reflexly activate the cardiovascular system. We have shown previously that topical application of histamine (HA) to the gastric wall causes reflex cardiovascular responses and have documented increased histamine concentrations in intestinal lymph and portal venous plasma during brief abdominal ischemia. In the present study, we hypothesized that histamine produced during ischemia activates ischemically sensitive C-fiber afferents by stimulation of H1 receptors. Nerve activity of single-unit abdominal visceral C-fiber afferents was recorded from the right thoracic sympathetic chain of anesthetized cats. Injection of histamine (25 micrograms/kg ia) significantly increased activity of nine ischemically sensitive C fibers from 0.09 +/- 0.06 to 1.11 +/- 0.20 imp/s. An H1-receptor agonist, 2-(3-chlorophenyl)histamine (250 micrograms/kg ia), also increased activity of these afferents from 0.11 +/- 0.04 to 0.64 +/- 0.18 imp/s (P < 0.05). Furthermore, an H1-receptor antagonist (pyrilamine, 0.2 mg/kg i.v.) significantly attenuated the increased activity in 11 other C fibers from 0.91 +/- 0.16 to 0.35 +/- 0.06 imp/s ischemia vs. pyrilamine + ischemia) and eliminated the response of 9 separate ischemically sensitive afferents to histamine. Conversely, both the H2-receptor agonist dimaprit (500 micrograms/kg ia) and the H3-receptor.agonist (R)-alpha-methylhistamine (250 micrograms/kg ia) did not significantly alter the activity of these nine afferents. In nine separate cats treated with indomethacin (5 mg/kg i.v.), pyrilamine (0.2 mg/kg i.v.) further significantly attenuated the increased activity in seven of nine C fibers during ischemia, and indomethacin (5 mg/kg i.v.) attenuated the response of eight other afferents to histamine. These data suggest that during mesenteric ischemia endogenous histamine contributes to the activation of afferents through direct stimulation of histamine H1 receptors and that histamine's stimulating effect on these afferents is dependent partially on production of prostaglandins.

Resident cardiac mast cells and the cardioprotective effect of ischemic preconditioning in isolated rat heart

Our study was designed to investigate the role of resident cardiac mast cells in the cardioprotective effect of ischemic preconditioning. Ischemic/compound 48/80 preconditioning and treatment with compound 48/80, a mast cell degranulator (1 microg/ml), produced cardioprotective and antiarrhythmic effects in isolated perfused rat heart subjected to 30-min global ischemia followed by 30-min reperfusion. Four episodes of ischemic/compound 48/80 preconditioning and compound 48/80 treatment markedly reduced the release of lactate dehydrogenase (LDH) and creatine kinase (CK) in coronary perfusate and the incidence of ventricular premature beats (VPBs) and ventricular tachycardia or fibrillation (VT/VF) during the reperfusion phase. The release of mast cell peroxidase (MPO), a marker of mast cell degranulation in coronary perfusate, increased immediately after ischemic and compound 48/80 preconditioning. The cardioprotective and antiarrhythmic effect of ischemic/compound 48/80 preconditioning was lost within 60 min. It is proposed that the cardioprotective effect of ischemic preconditioning, which lasts for 60 min in isolated rat heart, may be ascribed to degranulation of resident cardiac mast cells.

Histamine release and its effects in ischaemia-reperfusion injury of the isolated rat heart

Histamine is released from the heart during ischaemia-reperfusion injury. As histamine has cardiac effects, we investigated the role of histamine in ischaemia-reperfusion injury of isolated rat hearts. A Langendorff-model with 30 min global (37 degrees C) ischaemia followed by 60 min reperfusion was employed. The effects of ischaemia alone (n = 10, group 1.1 + n = 10, group 2.1, 2 different series), and ischaemia with H1- and H2-receptor blockade with cimetidine (10 microM, n = 10), chlorpheniramine (10 microM, n = 8), terfenadine (10 microM, n = 8), and promethazin (10 microM, n = 9), or both cimetidine and chlorpheniramine (n = 8), were studied. Histamine was measured in the coronary effluent and cardiac tissue of group 1.1. Release of histamine increased from 6.5 +/- 1 pmol min-1 before ischaemia to 19 +/- 3 pmol min-1 at the start of reperfusion. Ischaemia decreased left ventricular developed pressure to 18 +/- 11% (1.1) and 50 +/- 11% (2.1) of initial value (mean +/- SEM) at the start of reperfusion. Left ventricular end-diastolic pressure increased from 0 to 79 +/- 8 mmHg (1.1) and 39 +/- 9 (2.1) mmHg, while left ventricular systolic pressure was unchanged (101 +/- 12% in 1.1 and 101 +/- 10% in 2.1). Severe arrhythmias were induced in 90 (1.1) and 30 (2.1)% of the hearts, while coronary flow decreased during reperfusion. H2-blockade did not modify the changes in left ventricular pressures, coronary flow, or heart rate induced by ischaemia. Three different H1-blockers increased left ventricular systolic pressure, inhibited the decrease of developed pressure, attenuated the increase of end-diastolic pressure, and totally inhibited reperfusion arrhythmias. The effect of both blockers together was similar to that of H1-blockers alone. Coronary flow was increased during reperfusion in two of the groups with H1-blocker compared with ischaemic controls. Increased release of histamine from ischaemic-reperfused rat hearts concurred with depression of left ventricular function and arrhythmias during early reperfusion. Cardiac dysfunction during reperfusion was attenuated by three different H1-receptor blockers.

A critical review of the afferent pathways and the potential chemical mediators involved in cardiac pain

There is considerable evidence that on the anterior surface of the heart (which is usually supplied by the left anterior descending and the proximal part of the left circumflex coronary arteries), sympathetic efferent reflexes characterized by tachycardia and/or hypertension predominate following experimental or pathological perturbations. These cardiovascular reflexes are accompanied by an increase in presumed nociceptive afferent traffic and, in pathological condition, by pain. In these experiments, there is generally no effect of vagotomy on afferent nerve traffic, and lower cervical and upper thoracic sympathectomies help provide relief from angina. On the other hand, experimental or pathological perturbations involving the inferior-posterior surface of the heart (supplied by the right and distal parts of the left circumflex coronary arteries), are characterized by vagal efferent reflexes, resulting in bradycardia and/or hypotension. These reflexes are accompanied by an increase in vagal afferent nerve traffic and, in pathological conditions, by pain. In these experiments, vagotomy generally abolishes such cardiovascular reflexes, and lower cervical and upper thoracic sympathectomies are not effective in the relief from angina. Although cardiac sympathetic afferents are unquestionably involved in the central transmission of nociceptive information from the heart, it is also likely that there is a contributing role from the vagus in cardiac pain. It is important experimentally to understand the natural stimulus that gives rise to angina. In the clinical situation, a decrease in coronary blood flow or an increase in the metabolic demands of the myocardium due to increased work are obvious precipitating factors which lead to myocardial ischemia. In the experimental situation, occlusion of the coronary arteries is often used as a stimulus which mimics myocardial ischemia. As people who frequently experience angina have varying degrees of coronary artery disease, it is difficult to accept that the state of the coronary arteries of the normal experimental animal bear any resemblance to the state of the coronary arteries under pathological conditions. That is, the gain of homeostatic reflexes, the basal concentrations of neuroactive substances in the plasma, the myocardium and the afferent terminals, the excitability of the afferents, access of chemical mediators (e.g. bradykinin, 5-HT, adenosine, histamine, prostaglandins, potassium, lactate), to afferents, and the overall function of the animal are all significantly different. We have no idea how control mechanisms have been altered in the person with severe coronary artery disease compared to the normal patient or the "normal" experimental animal.(ABSTRACT TRUNCATED AT 400 WORDS)

Is there a role for an endothelium-derived relaxing factor in nociception?

Many of the circulating algesic agents released in response to ischemia produce a profound vasodilatation possibly through the release of an endothelium-derived relaxing factor (EDRF) as well as pain. We report here that intravenously administered S-nitrosocysteine, a putative EDRF, and not the nitric oxide liberating compound sodium nitroprusside produces significant alterations in nociceptive behavior that are abolished by bilateral vagotomy. These results are consistent with a role for EDRF in peripheral nociceptive mechanisms.

Histamine attenuates the arrhythmogenic effects of norepinephrine in hearts of spontaneously hypertensive rats

A potential physiological role for cardiac histamine and its interaction with norepinephrine were investigated in isolated left ventricles from spontaneously hypertensive rats (SHR). Prior to drug administration, left ventricle-to-body weight ratios and spontaneous firing rates (beats per min) were significantly increased in SHR ventricles vs. age- and sex-matched controls (WKY). Also, action potential duration was significantly prolonged in SHR at all levels of repolarization. In all hearts, norepinephrine (10(-7)-10(-4) M) increased spontaneous rate and the percent incidence of arrhythmias. The H2-receptor antagonist cimetidine (10(-5) M) potentiated the rate and arrhythmogenic effects of norepinephrine in SHR and, to a lesser extent, in WKY preparations; propranolol (10(-6) M) reduced them. Histamine (10(-7) M) also inhibited the norepinephrine-induced increase in arrhythmias in SHR, but not in WKY. The attenuation of adrenergically induced rhythm disturbances by histamine and their potentiation by cimetidine in hypertensive hearts support the hypothesis that histamine plays a role as a postjunctional modulator of adrenoceptor function in a setting of hypertension and myocardial hypertrophy.