Sympathetic histamine exerts different pre- and post-synaptic functions according to the frequencies of nerve stimulation in guinea pig vas deferens

Effect of Histamine H2 Receptor Antagonists on All-Cause Mortality in Critically Ill Patients With Essential Hypertension: A Retrospective Cohort Study

Previous studies found that histamine H2 receptor antagonists (H2RAs) had blood pressure lowering and cardioprotective effects, but the impact of H2RAs on the survival outcomes of critically ill patients with essential hypertension is still unclear. The aim of this study was to investigate the association of H2RAs exposure with all-cause mortality in patients with essential hypertension based on Medical Information Mart for Intensive Care III database. A total of 17,739 patients were included, involving 8482 H2RAs users and 9257 non-H2RAs users. Propensity score matching (PSM) was performed to improve balance between 2 groups that were exposed to H2RAs or not. Kaplan-Meier survival curves were used to compare the cumulative survival rates and multivariable Cox regression models were performed to evaluate the association between H2RAs exposure and all-cause mortality. After 1:1 PSM, 4416 pairs of patients were enrolled. The results revealed potentially significant association between H2RAs exposure and decreased 30-day, 90-day, and 1-year mortalities in multivariate analyses (HR = 0.783, 95% CI: 0.696-0.882 for 30-day; HR = 0.860, 95% CI: 0.778-0.950 for 90-day; and HR = 0.883, 95% CI: 0.811-0.961 for 1-year mortality, respectively). Covariate effect analyses showed that the use of H2RAs was more beneficial in essential hypertension patients with age ≥ 60, BMI ≥ 25 kg/m2, coronary arteriosclerosis, stroke, and acute kidney failure, respectively. In conclusion, H2RAs exposure was related to lower mortalities in critically ill patients with essential hypertension, which provided novel potential strategy for the use of H2RAs in essential hypertension patients.

Histamine H2 receptor antagonist exhibited comparable all-cause mortality-decreasing effect as β-blockers in critically ill patients with heart failure: a cohort study

Background: Our previous study reported that histamine H2 receptor antagonists (H2RAs) exposure was associated with decreased mortality in critically ill patients with heart failure (HF) through the same pharmacological mechanism as β-blockers. However, population-based clinical study directly comparing the efficacy of H2RAs and β-blockers on mortality of HF patients are still lacking. This study aims to compare the association difference of H2RAs and β-blockers on mortality in critically ill patients with HF using the Medical Information Mart for Intensive Care III database (MIMIC-III). Methods: Study population was divided into 4 groups: β-blockers + H2RAs group, β-blockers group, H2RAs group, and Non-β-blockers + Non-H2RAs group. Kaplan-Meier curves and multivariable Cox regression models were employed to evaluate the differences of all-cause mortalities among the 4 groups. Propensity score matching (PSM) was used to increase comparability of four groups. Results: A total of 5593 patients were included. After PSM, multivariate analyses showed that patients in H2RAs group had close all-cause mortality with patients in β-blockers group. Furthermore, 30-day, 1-year, 5-year and 10-year all-mortality of patients in β-blockers + H2RAs group were significantly lower than those of patients in β-blockers group, respectively (HR: 0.64, 95%CI: 0.50-0.82 for 30-day; HR: 0.80, 95%CI: 0.69-0.93 for 1-year mortality; HR: 0.83, 95%CI: 0.74-0.93 for 5-year mortality; and HR: 0.85, 95%CI: 0.76-0.94 for 10-year mortality, respectively). Conclusion: H2RAs exposure exhibited comparable all-cause mortality-decreasing effect as β-blockers; and, furthermore, H2RAs and β-blockers had additive or synergistic interactions to improve survival in critically ill patients with HF.

Effects of histamine on the contractility of the rat distal cauda epididymis

The motor activity of the epididymis duct is an essential process for male fertility and it is regulated by hormonal, neuronal and epithelial mechanisms. However, although there is evidence for the presence of histamine in the epididymis, its effects on epididymal motor activity are unknown. This study sought to evaluate the contractile effects of histamine on the rat distal cauda epididymis duct. Segments of the distal cauda epididymis duct from male Wistar rats were isolated and used in isolated organ bath experiments to evaluate the contractile effects of histamine in the absence or presence of antagonists of histamine receptors, α₁-adrenoceptors and muscarinic acetylcholine receptors. The effects of histamine on noradrenaline induced contractions were also investigated. Histamine was able to induce phasic contractions on rat distal cauda epididymis duct which were prevented by promethazine 10-1000 nM (H₁ receptor antagonist), ranitidine 1-100 μM (H₂ receptor antagonist), atropine 100 nM (muscarinic antagonist), and prazosin 100 nM (α₁-adrenoceptor antagonist). In addition, histamine was also able to modify noradrenaline-induced contractions possibly via activation of H₁ and H₂ receptors. In conclusion, this study demonstrates that histamine can induce phasic contractions of rat distal cauda epididymis via H₂ receptors and autonomic neurotransmitters. Histamine may also exert modulatory actions on contractions of rat distal cauda epididymis duct induced by adrenergic receptor agonists. Further studies are necessary to unveil the localization of histamine receptors within the epididymal duct and the consequences of manipulation of the histaminergic system on epididymal function and male fertility.

Histamine H2 receptor antagonist exposure was related to decreased all-cause mortality in critical ill patients with heart failure: a cohort study

BACKGROUND

Previous studies reported that histamine H2 receptor antagonists (H2RAs) had cardioprotective effects. However, the effect of H2RAs on mortality of critical ill patients with heart failure (HF) remains unclear. The aim of this study was to clarify the association between H2RAs and all-cause mortality of critical ill patients with HF based on Medical Information Mart for Intensive Care III database (MIMIC-III).

METHODS

Propensity score matching (PSM) was applied to account for the baseline differences between two groups that exposed to H2RAs or not. The study primary outcome was all-cause mortality. Kaplan-Meier curves and multivariable Cox regression models were employed to estimate the effects of H2RAs on mortality of critical ill patients with HF.

RESULTS

A total of 10 387 patients were included, involving 4440 H2RAs users and 5947 non-H2RAs users. After matching, 3130 pairs of patients were matched between H2RAs users and non-H2RAs users. The results showed significant association between H2RAs exposure and decreased 30-day, 90-day and 1-year mortality in both univariate analyses and multivariate analyses (HR = 0.73, 95%CI: 0.65-0.83 for 30-day; HR = 0.80, 95%CI: 0.72-0.89 for 90-day; and HR = 0.83, 95%CI: 0.76-0.90 for 1-year mortality, respectively) by Cox regression after PSM. Furthermore, stratified analyses revealed that the 30-day, 90-day and 1-year mortality of ranitidine users were significantly lower than those of famotidine users, respectively.

CONCLUSIONS

H2RAs exposure was associated with lower mortality in critical ill patients with HF. Furthermore, ranitidine might be superior to famotidine in reducing mortality of critical ill patients with HF.

Are Histamine H3 Antagonists the Definitive Treatment for Acute Methamphetamine Intoxication?

BACKGROUND

Methamphetamine (METH) is classified as a Schedule II stimulant drug under the United Nations Convention on Psychotropic Substances of 1971. METH and other amphetamine analogues (AMPHs) are powerful addictive drugs. Treatments are needed to treat the symptoms of METH addiction, chronic METH use, and acute METH overdose. No effective treatment for METH abuse has been established because alterations of brain functions under the excessive intake of abused drug intake are largely irreversible due in part to brain damage that occurs in the course of chronic METH use.

OBJECTIVE

Modulation of brain histamine neurotransmission is involved in several neuropsychiatric disorders, including substance use disorders. This review discusses the possible mechanisms underlying the therapeutic effects of histamine H₃ receptor antagonists on symptoms of methamphetamine abuse.

CONCLUSION

Treatment of mice with centrally acting histamine H₃ receptor antagonists increases hypothalamic histamine contents and reduces high-dose METH effects while potentiating lowdose effects via histamine H₃ receptors that bind released histamine. On the basis of experimental evidence, it is hypothesized that histamine H₃ receptors may be an effective target for the treatment METH use disorder or other adverse effects of chronic METH use.

Monoaminergic Receptors as Modulators of the Perivascular Sympathetic and Sensory CGRPergic Outflows

Blood pressure is a highly controlled cardiovascular parameter that normally guarantees an adequate blood supply to all body tissues. This parameter is mainly regulated by peripheral vascular resistance and is maintained by local mediators (i.e., autacoids), and by the nervous and endocrine systems. Regarding the nervous system, blood pressure can be modulated at the central level by regulating the autonomic output. However, at peripheral level, there exists a modulation by activation of prejunctional monoaminergic receptors in autonomic- or sensory-perivascular fibers. These modulatory mechanisms on resistance blood vessels exert an effect on the release of neuroactive substances from the autonomic or sensory fibers that modify blood pressure. Certainly, resistance blood vessels are innervated by perivascular: (i) autonomic sympathetic fibers (producing vasoconstriction mainly by noradrenaline release); and (ii) peptidergic sensory fibers [producing vasodilatation mainly by calcitonin gene-related peptide (CGRP) release]. In the last years, by using pithed rats, several monoaminergic mechanisms for controlling both the sympathetic and sensory perivascular outflows have been elucidated. Additionally, several studies have shown the functions of many monoaminergic auto-receptors and hetero-receptors expressed on perivascular fibers that modulate neurotransmitter release. On this basis, the present review: (i) summarizes the modulation of the peripheral vascular tone by adrenergic, serotoninergic, dopaminergic, and histaminergic receptors on perivascular autonomic (sympathetic) and sensory fibers, and (ii) highlights that these monoaminergic receptors are potential therapeutic targets for the development of novel medications to treat cardiovascular diseases (with some of them explored in clinical trials or already in clinical use).

Cardioprotective effect of histamine H2 antagonists in congestive heart failure: A systematic review and meta-analysis

BACKGROUND

Histamine H2 antagonists (H2RAs) have long been suggested to have beneficial effects on congestive heart failure (CHF). However, full agreement about the cardioprotective effects of H2RAs is still not reached yet. Therefore, this study aims to clarify the effects of H2RAs on myocardial function in CHF patients by meta-analysis.

METHODS

Electronic databases including PubMed, Embase, and Cochrane Library were retrieved. Randomized controlled trials comparing the cardiac effects of H2RAs and placebo or other medicines were collected. Pooled mean differences (MDs) with 95% confidence intervals (CIs) were calculated and meta-analysis was performed using RevMan 5.3 software.

RESULTS

A total of 10 studies (472 participants) were included in this meta-analysis. H2RAs exhibited significant negative inotropic and chronotropic effects to reduce heart rate (MD: -3.90; 95%CI: -7.07 to -0.73, P = .02). Furthermore, although H2RAs did not affect the blood pressure in health volunteers, they significantly decreased the blood pressure of CHF patients. Additionally, H2RAs were also associated with significant increase in pre-ejection period and the ratio of pre-ejection period to left ventricular ejection time.

CONCLUSION

In summary, these findings showed that H2RAs exerted negative inotropic and chronotropic effects to reduce heart rate and blood pressure, which, similar to beta-adrenergic receptor blockers, might decrease myocardial oxygen demand and eventually result in improvement of CHF symptoms. These data provided further evidence for the effect of H2RAs on cardiac function and novel potential strategy for treatment of CHF.

Antihistaminic and cardiorespiratory effects of diphenhydramine hydrochloride in anesthetized dogs undergoing excision of mast cell tumors

OBJECTIVE To evaluate the effects of IV diphenhydramine hydrochloride administration on cardiorespiratory variables in anesthetized dogs undergoing mast cell tumor (MCT) excision. DESIGN Randomized, blinded clinical trial. ANIMALS 16 client-owned dogs with MCTs. PROCEDURES In a standardized isoflurane anesthesia session that included mechanical ventilation, dogs received diphenhydramine hydrochloride (1 mg/kg [0.45 mg/lb], IV; n = 8) or an equivalent volume of saline (0.9% NaCl) solution (IV; control treatment; 8) 10 minutes after induction. Cardiorespiratory variables were recorded throughout anesthesia and MCT excision, and blood samples for determination of plasma diphenhydramine and histamine concentrations were collected prior to premedication (baseline), throughout anesthesia, and 2 hours after extubation. RESULTS Cardiorespiratory values in both treatment groups were acceptable for anesthetized dogs. Mean ± SD diastolic arterial blood pressure was significantly lower in the diphenhydramine versus control group during tumor dissection (52 ± 10 mm Hg vs 62 ± 9 mm Hg) and surgical closure (51 ± 10 mm Hg vs 65 ± 9 mm Hg). Mean arterial blood pressure was significantly lower in the diphenhydramine versus control group during surgical closure (65 ± 12 mm Hg vs 78 ± 11 mm Hg), despite a higher cardiac index value. Plasma histamine concentrations were nonsignificantly higher than baseline during maximal manipulation of the tumor and surgical preparation in the diphenhydramine group and during surgical dissection in the control group. CONCLUSIONS AND CLINICAL RELEVANCE IV administration of diphenhydramine prior to MCT excision had no clear clinical cardiorespiratory benefits over placebo in isoflurane-anesthetized dogs.

Relation of polymorphism of the histidine decarboxylase gene to chronic heart failure in Han Chinese

Histidine decarboxylase (HDC) is a key determinant of the levels of endogenous histamine that has long been recognized to play important pathophysiological roles during development of chronic heart failure (CHF). Meanwhile, certain genetic variants in HDC gene were reported to affect the function of HDC and associated with histamine-related diseases. However, the relation between polymorphisms of HDC gene and CHF risk remains unclear. This study aims to investigate the associations between 2 nonsynonymous HDC polymorphisms (rs17740607 and rs2073440) and CHF. We designed a 2-stage case-control study, in which we genotyped 439 patients with CHF and 467 healthy controls recruited in Xi'an, China, and replicated this study in 413 patients with CHF and 452 healthy subjects in Kunming, China. We also performed in vitro experiments to further validate the functional consequences of variants positively associated with CHF. The rs17740607 polymorphism showed replicated associations with all-cause CHF according to genotype and allele distribution and also under a dominant and additive genetic model after adjusted for traditional cardiovascular-related factors. Functional experiments further demonstrated that rs17740607 polymorphism decreased the HDC activity. In conclusion, HDC rs17740607 polymorphism is at least a partial loss-of-function variant and acts as a protective factor against CHF, which provides novel highlights for investigating the contribution of CHF.

Arrhythmogenic effect of sympathetic histamine in mouse hearts subjected to acute ischemia

The role of histamine as a newly recognized sympathetic neurotransmitter has been presented previously, and its postsynaptic effects greatly depended on the activities of sympathetic nerves. Cardiac sympathetic nerves become overactivated under acute myocardial ischemic conditions and release neurotransmitters in large amounts, inducing ventricular arrhythmia. Therefore, it is proposed that cardiac sympathetic histamine, in addition to norepinephrine, may have a significant arrhythmogenic effect. To test this hypothesis, we observed the release of cardiac sympathetic histamine and associated ventricular arrhythmogenesis that was induced by acute ischemia in isolated mouse hearts. Mast cell-deficient mice (MCDM) and histidine decarboxylase knockout (HDC(-/-)) mice were used to exclude the potential involvement of mast cells. Electrical field stimulation and acute ischemia-reperfusion evoked chemical sympathectomy-sensitive histamine release from the hearts of both MCDM and wild-type (WT) mice but not from HDC(-/-) mice. The release of histamine from the hearts of MCDM and WT mice was associated with the development of acute ischemia-induced ventricular tachycardia and ventricular fibrillation. The incidence and duration of induced ventricular arrhythmias were found to decrease in the presence of the selective histamine H(2) receptor antagonist famotidine. Additionally, the released histamine facilitated the arrhythmogenic effect of simultaneously released norepinephrine. We conclude that, under acute ischemic conditions, cardiac sympathetic histamine released by overactive sympathetic nerve terminals plays a certain arrhythmogenic role via H(2) receptors. These findings provided novel insight into the pathophysiological roles of sympathetic histamine, which may be a new therapeutic target for acute ischemia-induced arrhythmias.

Effects of sympathetic histamine on vasomotor responses of blood vessels in rabbit ear to electrical stimulation

OBJECTIVE

To investigate the effects of histamine receptor antagonists on vasoconstriction induced by electrical stimulation (ES) on posterior auricular nerve, and to explore the pre- and post-synaptic effects of sympathetic histamine on the vasomotor responses of vascular smooth muscle in rabbit ear.

METHODS

ES was applied to posterior auricular nerves of the whole rabbit ear at 10 Hz, 20 Hz and 40 Hz, respectively. Besides, the whole ear was perfused with different histamine receptor antagonists under constant perfusion pressure, and the changes in the flow rate of perfusate were observed.

RESULTS

The flow rate of venous outflow was decreased by ES at all the 3 frequencies. The ES-induced vasoconstriction at 20 Hz and 40 Hz could be partly inhibited by H(1) receptor antagonist chlorpheniramine (P < 0.05). After exhaustion of histamine in mast cells by pretreatment with specific mast cell degranulator compound 48/80, chlorpheniramine could still inhibit the ES-induced flow rate reduction. In contrast, H(2) receptor antagonist cimetidine could enhance the 40-Hz ES-induced flow rate reduction (P < 0.05). Moreover, ES-induced vasoconstriction at the 3 frequencies could all be enhanced by H(3) receptor antagonist thioperamide (P < 0.05).

CONCLUSION

Stimulation on the auricular nerve may evoke histamine release from sympathetic nerves rather than from mast cells. Moreover, the functions of sympathetic histamine vary from pre-synaptic modulation to post-synaptic vasoconstriction or vasodilatation, via activation of different histamine receptors.