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Background: Having a comprehensive map of the cellular anatomy of the normal human bladder is vital to understanding the cellular origins of benign bladder disease and bladder cancer., Methods: We used single-cell RNA sequencing (scRNA-seq) of 12,423 cells from healthy human bladder tissue samples taken from patients with bladder cancer and 12,884 cells from mouse bladders to classify bladder cell types and their underlying functions., Results: We created a single-cell transcriptomic map of human and mouse bladders, including 16 clusters of human bladder cells and 15 clusters of mouse bladder cells. The homology and heterogeneity of human and mouse bladder cell types were compared and both conservative and heterogeneous aspects of human and mouse bladder evolution were identified. We also discovered two novel types of human bladder cells. One type is ADRA2A + and HRH2 + interstitial cells which may be associated with nerve conduction and allergic reactions. The other type is TNNT1 + epithelial cells that may be involved with bladder emptying. We verify these TNNT1 + epithelial cells also occur in rat and mouse bladders., Conclusions: This transcriptomic map provides a resource for studying bladder cell types, specific cell markers, signaling receptors, and genes that will help us to learn more about the relationship between bladder cell types and diseases., (Copyright © 2019 by the American Society of Nephrology.)

Flow cytometry is one of the most widely used methods for the qualitative and quantitative analysis of cell surface expressed proteins by making use of fluorescent specific antibodies. Lacking an antibody validated for flow cytometry, an alternative approach for labeling cell surface receptors is the use of fluorescently tagged ligands. In this study, histamine H4 receptor transfected Chinese hamster ovary cells and murine bone marrow-derived mast cells (mBMMCs) were selected for studying the possibility of staining individual histamine receptors using BODIPY(®) FL histamine and selective antagonists. Flow cytometric measurements and supporting calculations showed that BODIPY FL histamine is suitable tool for quantitating cell surface histamine receptors. The binding, and competitive inhibition of this fluorescent ligand were characterized, which were in good agreement with a semi-empirical model constructed from fundamental protein-binding relationships. Using this method it was shown for the first time that even though mature mBMMCs express H2R and H4R to the same extent, immunoglobulin E sensitization results in H4R upregulation only, while the surface expression of H2R remains unchanged., (© 2014 International Society for Advancement of Cytometry.)

Objectives: Histamine is a known inducer of cAMP-responsive element binding protein (CREB), which plays a key role in initiation of adipogenesis. Our present goal was to study how histamine deficiency impacts CREB signalling and adipogenesis., Methods: We used a histidine-decarboxylase gene-targeted (HDC KO) mice model lacking endogenous histamine. We measured CREB activity and expression by EMSA, Western blot and real-time RT-PCR, as well as cAMP levels by ELISA in primary embryonic fibroblasts derived from WT and HDC KO mice. The ability of these cells to form adipocytes was also tested in preliminary experiments., Results: We found that in the absence of the histamine, cells show higher constitutive CREB activity and greatly increased intracellular cAMP levels, as well as that in contrast to WT cells, HDC KO fibroblasts are more prone to differentiate into adipocytes., Conclusion: These data suggest a newly recognised inhibitory role for histamine in CREB activity and draws attention to the potential role of histamine in adipocyte differentiation.

The aim of the present study was to investigate the effect of histamine, a product of e.g. mast cells, on short-circuit current (I(sc)) across rat distal colon. Histamine concentration-dependently stimulated an increase in I(sc), which often was preceded by a transient negative current. Neither a release of neurotransmitters nor a release of prostaglandins contributed to the histamine response. The histamine-induced increase in I(sc) was blocked by the histamine H(1) antagonist, pyrilamine, but was resistant against the histamine H(2) antagonist, cimetidine. Conversely, the histamine H(1) agonist, TMPH (2-(3-trifluoromethylphenyl)histamine), exclusively evoked an increase in I(sc), whereas the histamine H(2) agonist, amthamine, evoked only a decrease in I(sc) suggesting that stimulation of different types of histamine receptors is responsible for the two phases of the response evoked by native histamine. Histamine induces the opening of glibenclamide-sensitive Cl(-) channels and of charybdotoxin-sensitive K(+) channels in the apical membrane as demonstrated by experiments at basolaterally depolarized epithelia. A further action site is the basolateral membrane, because histamine stimulates a charybdotoxin- and tetrapentylammonium-sensitive K(+) conductance in this membrane as observed in tissues, in which the apical membrane was permeabilized with an ionophore, nystatin. The increase in I(sc) evoked by histamine was blocked after depletion of intracellular Ca(2+) stores with cyclopiazonic acid and after blockade of inositol 1,4,5-trisphosphate (IP(3)) receptors, suggesting a release of stored Ca(2+). This was confirmed by the observation that the histamine H(1) agonist TMPH induced an increase in the fura-2 ratio signal of epithelial cells within isolated colonic crypts. Consequently, the mediator histamine seems to stimulate both histamine H(1) and H(2) receptors, from which the former seems to be prominently involved in the induction of epithelial chloride secretion.

Background and Aims: Histamine is known as a regulator of gastrointestinal functions, such as gastric acid production, intestinal motility, and mucosal ion secretion. Most of this knowledge has been obtained from animal studies. In contrast, in humans, expression and distribution of histamine receptors (HR) within the human gastrointestinal tract are unclear., Methods: We analysed HR expression in human gastrointestinal tissue specimens by quantitative reverse transcription-polymerase chain reaction and immunostaining., Results: We found that H1R, H2R, and H4R mRNA were expressed throughout the gastrointestinal tract, while H3R mRNA was absent. No significant differences in the distribution of HR were found between different anatomical sites (duodenum, ileum, colon, sigma, and rectum). Immunostaining of neurones and nerve fibres revealed that H3R was absent in the human enteric nervous system; however, H1R and H2R were found on ganglion cells of the myenteric plexus. Epithelial cells also expressed H1R, H2R and, to some extent, H4R. Intestinal fibroblasts exclusively expressed H1R while the muscular layers of human intestine stained positive for both H1R and H2R. Immune cells expressed mRNA and protein for H1R, H2R, and low levels of H4R. Analysis of endoscopic biopsies from patients with food allergy and irritable bowel syndrome revealed significantly elevated H1R and H2R mRNA levels compared with controls., Conclusions: We have demonstrated that H1R, H2R and, to some extent, H4R, are expressed in the human gastrointestinal tract, while H3R is absent, and we found that HR expression was altered in patients with gastrointestinal diseases.

Objective: Histamine may have physiologic functions in the inner ear. The locations of histamine receptors, however, have not yet been identified in the mammalian cochlea. The aim of this study was to investigate the localization of histamine receptor subtypes (H1, H2, and H3 receptors) in rat cochlea., Methods: Immunohistochemistry was performed with antibodies specific for each of the histamine receptors (H1, H2, and H3). To identify the type I and II spiral ganglion cells in the cochlea, some cryostat sections were double stained with antibodies to both a histamine receptor and neurofilament 200 kD, which predominantly stains type II spiral ganglion cells in the cochlea., Results: All H1, H2, and H3 receptor immunoreactive staining was limited to the spiral ganglion cells of the cochlea. Spiral ganglion cells with positive immunoreactivity to the neurofilament 200 kD antibody were stained only slightly by histamine H1, H2, and H3 receptor antibodies, indicating that histamine receptor immunoreactivity is specific to type I ganglion cells., Conclusions: These findings indicate that histamine receptors are present in the cochlea and support the hypothesis that histamine plays a physiologic role in the cochlea.

Human monocyte-derived dendritic cells (MoDC) have both histamine H1 and H2 receptors and can induce CD86 expression by histamine. Nevertheless, it has not been reported whether human epidermal Langerhans cells (LC) have histamine receptors or not. In this study, using RT-PCR, we investigated the expression of H1 and H2 receptor mRNA on DC with the features of LC (LC-like DC) that were generated in vitro from peripheral blood monocytes, LC derived from CD34+ hematopoietic progenitor cells, and LC obtained from human epidermis. We compared the histamine-induced CD86 expression among these cells. In contrast to MoDC, LC and LC-like DC did not express H1 or H2 receptors. In addition, they could not augment the CD86 expression by histamine. Interestingly, when transforming growth factor-beta1 (TGF-beta1) was added to the culture of MoDC, the expression of H1 and H2 receptors and the histamine-induced CD86 expression were abrogated in a concentration-dependent fashion. Finally, in the assessment of the cell surface expression of histamine receptors using fluorescence-labeled histamine, histamine could bind to MoDC and dermal dendritic cells obtained from the skin, whereas there was no specific binding of histamine to LC-like DC or LC obtained from the skin. These data suggest that LC do not express either H1 or H2 receptors, mainly because of the effect of TGF-beta1. This made a striking contrast with the expression of the functional H1 and H2 receptors on MoDC and dermal dendritic cells.

Histamine and antihistamines are so deeply woven into the fabric of allergic diseases that it is sometimes difficult to see how this field could advance beyond our current, potent histamine H1-receptor drugs. Investigations of other actions of histamine and the identification of H2, H3, and now H4 receptors have suddenly reignited the search for new mono- and multi-receptor-specific agonists and antagonists. There is great excitement due to preliminary findings that H3 receptors act as neural inhibitory autoreceptors, and H4 receptors might modulate immune cell functions.

The distribution of histamine H(2) receptor mRNA was determined by in situ hybridization histochemistry in human and monkey brain. In the case of monkey brain, we combined this technique with receptor ligand autoradiography to compare the distribution of mRNA and receptor binding sites. [(125)I]Iodoaminopotentidine ([(125)I]-APT), a reversible, high specific activity antagonist with high affinity and selectivity for the H(2) receptor, was used for receptor autoradiography. Radiolabeled oligonucleotides derived from the human mRNA sequence encoding this receptor were used as hybridization probes. The highest density of the H(2) receptor mRNA in human and monkey brain was found in caudate and putamen nuclei and external layers of cerebral cortex. Moderate levels were seen in the hippocampal formation and lower densities in the dentate nucleus of cerebellum. Areas such as globus pallidus, amygdaloid complex, cerebellar cortex, and substantia nigra were devoid of hybridization signal. The distribution of H(2) receptor mRNA in monkey brain is generally in good agreement with that of the corresponding binding sites: prominent in caudate, putamen, accumbens nuclei, and cortical areas. The hippocampus showed lower densities of receptors and low levels were detected in the globus pallidus pars lateralis. No binding sites were seen in amygdaloid complex and substantia nigra. The distribution of histaminergic innervation is in good correlation with the areas of high density for H(2) receptors: caudate, putamen, and external layers of cerebral cortex in monkey and human brain. The presence of mRNA in caudate and putamen nuclei, together with its absence from substantia nigra, suggests that the H(2) receptors found in the striatum are synthesized by intrinsic cells and not by nigral dopaminergic cells. These striatal H(2) receptors may be located on short circuit striatal interneurons or somatodendritically on striatal projection neurons which project to the globus pallidus pars lateralis. In conclusion, the present results, which constitute, to our knowledge, the first report of the regional distribution of mRNA encoding H(2) receptors detected by in situ hybridization, define the sites of synthesis of H(2) receptors and are the basis for future, more detailed studies that should result in a better understanding of H(2) receptor function., (Copyright 2000 Wiley-Liss, Inc.)

mRNA encoding histamine H1 and H2 receptors were detected in the human nasal mucosa using reverse transcriptase-polymerase chain reaction. The possibility of local release in connection with specific target receptors suggests a role for histamine in the regulation of vascular tone, glandular secretion and epithelial functions.

[Ca2+]i and whole-cell membrane current were measured in microvascular endothelial cells from bovine brain. The effects of histamine on [Ca2+]i were examined, and the acute effect of changing extracellular glucose concentration on Ca2+ homeostasis was investigated. Application of 10 micromol/l histamine evoked an initially transient and then sustained increase in [Ca2+]i in normal Krebs solution, but only the transient component in Ca2+-free solution, thereby indicating that histamine mobilizes Ca2+ both from intracellular store sites and extracellular space. The effects of histamine on [Ca2+]i were inhibited by the H2 antagonists, ranitidine and cimetidine, but not by the H1 antagonist, pyrilamine. Incubation of the cells for 2 h in solutions containing low (1.1 and 2.3 mmol/l) or high (23 mmol/l) concentrations of glucose did not influence the resting level of [Ca2+]i. Treatment with low concentrations of glucose did not impair histamine-induced Ca2+ mobilization. On the other hand, when histamine was applied to the cells pretreated with 23 mmol/l glucose, it failed to mobilize Ca2+ from both intracellular store sites and extracellular space. The effect of histamine was mimicked by dibutyryl cyclic AMP, but glucose overload failed to inhibit this, suggesting that glucose overload inhibits H2 receptor-mediated cyclic AMP production. Glucose overload-induced impairment of histamine action was reversed by pretreatment with staurosporine and calphostin C and mimicked by phorbol-12,13-dibutyrate, thereby suggesting the involvement of protein kinase C in the high glucose-induced inhibition of Ca2+ mobilization. Whole-cell membrane current measurement showed that there was no difference in the membrane currents between control and high glucose-treated cells. These results indicate that in bovine brain microvascular endothelial cells, histamine induces Ca2+ release from intracellular store sites and subsequent entry from the extracellular space through the activation of H2 receptors. Glucose overload acutely inhibits histamine-induced Ca2+ mobilization by the activation of protein kinase C.

Histamine H2 receptors were tagged at the N-terminus with the eight amino acid Flag epitope to allow the immunological identification of the receptor peptide with the monoclonal anti-Flag M2 antibody. The introduction of the epitope did not modify the binding of several H2 ligands to the H2 receptor, nor the ability of histamine to stimulate the H2 receptor mediated cAMP production in HEK-293 cells. Western blots revealed a major protein band of 57 +/- 1 kDa, whereas a second band of 31 +/- 1 kDa was probably the result of a proteolytic breakdown of the 57 kDa band. Immunofluorescence measurements of stably transfected HEK-293 cells revealed the presence of anti-Flag-immunoreactivity in the plasma membrane. This immunoreactivity completely disappeared after a one hour treatment with histamine. The receptor internalization was reversible and blocked by the endocytosis inhibitor phenylarsine oxide. Forskolin did not induce H2 receptor internalization, indicating that histamine causes H2 receptor internalization via a cAMP-independent pathway.

Classic physiological and pharmacological experiments were made on 33 rabbits under hexenal anesthesia to determine the presence, topical concentration and activity of H2 and B2-receptors. These parameters were inferred by edema and other vascular responses of the mucosa to local application of histamine and bradykinin prior to and after usage of specific blocker of each receptor type. Both mediators and receptor blockers were applied to laryngeal and tracheal mucosa for 10 min (histamine 10(-4) and 10(-3) g/ml, H2-receptor blocker metiamide 0.1 and 1 mmol, bradykinin 10(-5) and 10(-4) g/ml, B2-receptor blocker pyridinolcarbamate 10(-2) and 10(-1) g/ml). The larynx and trachea were found to contain H2- and B2-receptors the concentrations of which were greater in the subvocal part of the larynx than in the vestibular part and trachea. B2-receptor activity and concentrations in the subvocal part of the larynx were 10 times while in the trachea 1.5-2 times greater than those of H2-receptors. These regularities were not influenced by individual varieties of receptor topical concentrations. The blocker density in the receptors and the duration of their binding were not universally proportional. This is also true for the relations mediator-receptor. Concentrations and activity of H2- and B2-receptors are thought important in pathogenesis and location of acute inflammatory and allergic conditions in the upper respiratory tract.

We investigated effects of the biogenic diamine histamine on antibody-dependent cellular cytotoxicity (ADCC) against autologous anti-D-coated red blood cells mediated by human granulocytes, monocytes, and natural killer (NK) cells. Effector cells were separated from peripheral blood by countercurrent centrifugal elutriation. ADCC of monocytes and neutrophilic granulocytes was suppressed by histamine. ADCC of enriched CD3-/56+ NK cells was unchanged by histamine. ADCC of NK cells was effectively inhibited by elutriated monocytes or neutrophils. Histamine completely reversed the inhibition of NK cell-mediated ADCC induced by monocytes and partly reversed the inhibition induced by neutrophils; thereby, histamine augmented ADCC of NK cells in the presence of monocytes or neutrophils. The indirect effect of histamine on ADCC of NK cells and the effect of histamine on ADCC of monocytes/neutrophils were completely antagonized by the specific H2 receptor (H2R) blocker ranitidine. We conclude that activation of H2R suppresses ADCC reactivity of monocytes/neutrophils and, concomitantly, promotes ADCC reactivity of NK cells by abrogating a phagocyte-derived, suppressive signal.

In contrast with many physiological studies suggesting that histamine H2 receptors are present on acid-secreting parietal cells of the gastric epithelium, it was recently shown that immune cells in the lamina propria are the only cells expressing H2-receptor mRNAs (Mezey and Palkovits, Science, 1992, 258, 1662-1665). We have reinvestigated the cellular localization of H2 receptors in the rat stomach by visualizing both the H2 receptor mRNA and the H2-receptor protein itself. In situ hybridization histochemistry performed with an antisense riboprobe for the rat H2 receptor, and autoradiographic distribution of 125I-aminopotentidine binding sites, a highly selective H2-receptor ligand, did not show any labeling of the lamina propria. Signals were clearly and solely detected in the gastric epithelium, the strongest being observed in the upper part of the glands where the H2 receptor gene transcripts were only detected within parietal cells. In situ hybridization performed with an antisense riboprobe for L-histidine decarboxylase mRNA confirmed the basal localization of the histamine-synthetizing cells in the rat gastric gland, at some distance from parietal histamine-sensitive cells.

Histamine receptors on bovine peripheral blood lymphocytes (PBL) were detected by three different methods: a rosetting technique, binding to histamine-bearing Sepharose beads and immunofluorescence staining. The rosetting technique used histamine-rabbit serum albumin (H-RSA) conjugated to bovine red blood cells to detect histamine receptors and this showed that 10.8% of bovine PBL were positive. A method using H-RSA conjugate coupled Sepharose beads also detected histamine receptor bearing PBL but was not quantitative. The indirect immunofluorescence method, by which the subpopulation of histamine receptor bearing lymphocytes can be easily double stained to concurrently identify the B cell marker, revealed that PBL, the B cell and T cell fraction of bovine PBL contained 18.4, 52.8 and 9.3% histamine receptor bearing cells, respectively. This method was found to be more stable and more easily quantifiable than the other two methods. Blocking tests using the histamine H1 receptor antagonist diphenhydramine and the histamine H2 receptor antagonist cimetidine suggested that bovine PBL have both H1 and H2 receptors on their surfaces. Addition of histamine into cultures of PBL at the concentration range 10(-6) to 10(-3) M suppressed the response of PBL to the mitogen phytohemagglutinin. The histamine induced suppression of mitogenesis could be reduced partially by the H2 receptor antagonist cimetidine, but not by the H1 antagonist diphenhydramine. It is possible that histamine induced suppression of PBL mitogenesis was mediated by H2 receptors on T cells.

Autoradiographic techniques were used to study the distribution of histamine H2-receptors as labeled with [125I]iodoaminopotentidine in the brains of patients affected by human neurodegenerative pathologies, as compared with control cases. The highest levels of histamine H2 binding sites in control cases were found in the caudate, putamen, and accumbens nuclei. In Huntington's chorea, the levels of histamine H2-receptor binding sites were found to be markedly decreased in virtually all regions examined, particularly in the putamen and globus pallidus lateralis. The loss of binding sites was related to the grade of the disease. Losses were more marked in grade III disease cases. The possible influence of neuroleptic treatment, commonly used in Huntington's patients, was studied by including samples from clinically treated schizophrenic patients. A moderate increase in the densities of [125I]iodoaminopotentidine was found in the globus pallidus of these patients. In Parkinson's disease, the levels of histamine H2-receptor binding sites were found not to be significantly different from those of control cases. These results were comparable with those obtained from unilaterally neurotoxin-lesioned guinea pigs. Similar losses of binding sites were observed in the quinolinic acid lesioned striatal intrinsic neurons in the guinea pig, whereas lesioning dopaminergic cell bodies in the substantia nigra with 6-hydroxydopamine did not produce any significant change. These results strongly suggest that histamine H2-receptors are expressed by striatal neurons, which degenerate in Huntington's chorea, but not by nigral dopaminergic neurons and may play a role in the regulation of the intact striato-nigral pathway.

Data on human lung histamine H1- and H2-receptors in cancer and chronic inflammatory processes are reported. It has been found that the number of histamine H1-receptors significantly increases both in cancer and chronic pneumonia and does not practically change in tuberculosis lung parenchyma. The binding parameters of histamine H2-receptors both in cancer and inflammatory processes were similar to those obtained for the normal tissue. The important role of parenchymal histamine H1-receptors in the neuromodulation of airways in human lung adenocarcinoma is discussed.

Histamine receptors were characterized in muscle cells isolated from the longitudinal muscle layer of guinea pig intestine. Histamine caused concentration-dependent contraction and stimulated significant increases in [Ca++]i (141 +/- 16 nM, P < .001) and cyclic AMP (cAMP) (10.3 +/- 0.5 pmol/10(6) cells, P < .001). The H1 receptor antagonist, mepyramine, inhibited contraction and the increase in [Ca++]i, whereas the H2 receptor antagonist, cimetidine, augmented contraction and the increase in [Ca++]i (277 +/- 31 nM, P < .01) and abolished the increase in cAMP. In cells maximally contracted with a nonhistamine agonist [cholecystokinin octapeptide (CCK)], histamine caused concentration-dependent relaxation when the contractile effect mediated by H1 receptors was blocked with mepyramine; relaxation was inhibited by cimetidine in a concentration-dependent fashion. The effects mediated by H1 and H2 receptors were characterized further in cells in which only one receptor type was preserved by selective receptor protection. In cells in which only H1 receptors were preserved, histamine caused contraction that was inhibited by mepyramine; no relaxation of CCK-induced contraction could be elicited by histamine in the presence of mepyramine. Conversely, in cells in which only H2 receptors were preserved, histamine had little or no contractile effect by itself but caused relaxation of CCK-induced contraction in the absence of mepyramine. We conclude that in, intestinal muscle cells, H1 receptors mediating Ca(++)-dependent contraction coexist with H2 receptors mediating cAMP-dependent relaxation. The effect of histamine reflects activation of dominant H1 receptors as well as of H2 receptors which act to attenuate [Ca++]i and contraction by stimulating an increase in intracellular cAMP.

Histamine receptors in pig basilar arteries were investigated in vitro by radioligand binding assays and by measuring the contractile and relaxant responses to histamine. Histamine and 2-pyridylethylamine (H1-agonist) induced concentration-dependent contractions, whereas impromidine (H2-agonist) induced concentration-dependent relaxations. These responses were independent of the presence of endothelial cells. Diphenhydramine (H1-antagonist) partially reversed the histamine-induced contractions to relaxations. Cimetidine (H2-antagonist) potentiated the contraction in a concentration-dependent manner. In the presence of cimetidine, the pEC50 value of histamine for the contraction was 6.30, and diphenhydramine competitively antagonized the histamine-induced contractions (pA2, 7.77). In the presence of diphenhydramine, the pEC50 value of histamine for the relaxation was 5.93, and cimetidine competitively antagonized the histamine-induced relaxations (pA2, 6.62). In the binding studies, the Kd value of [3H]mepyramine was 2.1 nM and the Bmax value was 95.6 fmol/mg protein. A competition experiment with diphenhydramine showed that the pKi value (7.51) was similar to the pA2 value. The Kd value for [3H]cimetidine was 126.0 nM and the Bmax value was 459.8 fmol/mg protein. The pKd (6.90) for [3H]cimetidine was similar to the pA2 for cimetidine. The Hill coefficients for these experiments were not significantly different from unity. The present findings indicate that the number of H1-receptors, in terms of the Bmax value for [3H]mepyramine, is smaller than that of H2-receptors, in terms of the Bmax value for [3H]cimetidine. However, the contractile response to histamine is predominantly mediated through stimulation of H1-receptors on vascular smooth muscle cells in pig basilar artery.

In pithed and vagotomized rats the effects of the H3 receptor agonist R-(-)-alpha-methylhistamine, the H1 receptor agonist 2-(2-thiazolyl)ethylamine and the H2 receptor agonist dimaprit on basal diastolic blood pressure, basal heart rate and the electrically induced rise in heart rate were examined. Basal diastolic blood pressure was not altered by low, but increased by high doses of R-(-)-alpha-methylhistamine; the latter effect was not affected by selective H1, H2 or H3 receptor antagonists and by prazosin, but was attenuated by rauwolscine. Rauwolscine also unmasked a vasodepressor response to R-(-)-alpha-methylhistamine not affected by the H3 receptor antagonist thioperamide, but counteracted by the H1 receptor antagonist dimetindene or the H2 receptor antagonist ranitidine. The vasodepressor responses to 2-(2-thiazolyl)ethylamine and dimaprit were antagonized by dimetindene and ranitidine, respectively. The vasodepressor response to 2-(2-thiazolyl)ethylamine was not altered by indomethacin, but reduced by an inhibitor of endothelial nitric oxide synthase, N omega-nitro-L-arginine methyl ester (which, by itself, markedly increased blood pressure). Both drug tools did not alter the effect of dimaprit. Basal heart rate was not affected by 2-(2-thiazolyl)ethylamine (examined after administration of propranolol), dimaprit and R-(-)-alpha-methylhistamine. The electrically induced increase in heart rate (studied in animals which had received rauwolscine) was decreased by R-(-)-alpha-methylhistamine but not affected by 2-(2-thiazolyl)ethylamine and dimaprit. The effect of R-(-)-alpha-methylhistamine was abolished by thioperamide. R-(-)-alpha-methylhistamine did not influence the increase in heart rate produced by isoprenaline.(ABSTRACT TRUNCATED AT 250 WORDS)

Does gastrin stimulate gastric acid secretion by direct action on oxyntic cells, by releasing histamine, or by being potentiated by histamine? Previous studies in the mouse pointed to gastrin-regulated histamine release. Guinea pig and rat are well known to vary in their sensitivity to histamine. Therefore, the effects of histamine and pentagastrin were compared quantitatively on isolated, lumen-perfused, stomach preparations from these species in the absence and presence of histamine H2-receptor blockade. The loss of potency of histamine in the rat was mirrored by a loss of potency of pentagastrin consistent with the idea that pentagastrin acts by releasing histamine. In the rat, a well-defined pentagastrin curve was obtained in the presence of histamine H2-receptor block as though pentagastrin acts both directly on the oxyntic cell and indirectly by releasing histamine. It was not necessary to invoke a potentiating interaction between histamine and pentagastrin at the oxyntic cell; the two effects appeared simply to add. Potentiation was observed, however, between other combinations of stimuli, for example, between vagal nerve and pentagastrin stimulation. The physiological consequences of these results are discussed.

The identification and quantitative analysis of specific histamine H1 and H2 receptors on lymphocytes were acquired and histamine-induced suppressor cell activity was examined by using 3H-histamine radioligand-binding assay and co-culture technique. The quantitative analysis of H2 receptors decreased on the lymphocytes of extrinsic asthmatic subjects. Peripheral-lymphocytes from asthmatic subjects generated less histamine-induced suppressor activity than did those from normal individuals. In the asthmatics, the functional suppressor-cell abnormality positively correlated with the decreased quantity of H2 receptors on the lymphocytes.

The phenotypes of two different types of suppressor T cells in the chicken, both capable of inhibiting secondary antibody responses in vitro, were determined. The first of these, induced by injection of concanavalin A (Con A) into normal chickens, was CT8+, TcR2+ (alpha beta), CT4-, TcR1- (gamma delta). These cells appeared to exhibit histamine type 2 (H2) receptors, as they adhered to cimetidine-BSA-coated dishes. Moreover, cimetidine added to the medium at 2 x 10(-4) M completely prevented the suppression induced by these suppressor cells. The second type of 'suppressor' T-cell studied, induced in agammaglobulinaemic (A gamma) chickens by injection of bursa cells, exhibited the same phenotype, but was insensitive to cimetidine and did not adhere to cimetidine-BSA-coated dishes, indicating heterogeneity with respect to H2 receptor expression on CT8+ chicken T cells with suppressor activity. The results also showed that a relatively larger proportion of CT8+ than of CT4+ cells adhered to cimetidine-BSA-coated dishes and thus appeared to be H2 receptor positive. TcR1 (gamma delta) cells did not contribute significantly to the antigen non-specific suppressor effects examined in this study.

The distribution of histamine H1, H2 and H3 receptors in postmortem human and rhesus monkey brain was examined using receptor autoradiography. [125I]Iodobolpyramine, [125I]iodoaminopotentine and [3H](R) alpha-methylhistamine were used as ligands to label H1, H2 and H3 receptors respectively. The 3 receptor subtypes were identified in the human and monkey brains. Each receptor presented comparable distribution in the two primate brains. H1 and H2 receptors were particularly enriched in the caudate and putamen and observed in other brain areas such as the neocortex and hippocampus. H3-receptors were found to predominate in the basal ganglia where the highest densities were localized in the two segments of the globus pallidus. They were also observed in the hippocampus and cortical areas. The distribution of these 3 histamine receptors in the primate brain suggests the involvement of histaminergic mechanism in the functions of many brain areas. In particular, H2 and H3 receptors could play a role in the regulation of the basal ganglia functions in primates.

This study was performed to determine the subtypes of histamine receptors that are involved in the electrophysiological, inotropic and biochemical responses to histamine in isolated rabbit papillary muscles. Histamine increased force of contraction and shortened action potential duration (APD) in a concentration-dependent manner. The former was antagonized by chlorpheniramine, a H1-antagonist, whereas the latter was blocked by cimetidine, a H2-antagonist. However, even when H1-receptors were blocked entirely by chlorpheniramine, histamine still produced a positive inotropic effect, an effect which was antagonized by cimetidine. On the other hand, when H2-receptors were eliminated by cimetidine, histamine caused a H1-receptor mediated APD prolongation. Carbachol attenuated the decrease in APD but not the increase in force of contraction caused by histamine. Cyclic AMP and cyclic GMP levels both were elevated significantly by histamine. The increase in cyclic AMP level induced by histamine was abolished by cimetidine, but not altered by chlorpheniramine, whereas the converse was true for the increase in cyclic GMP level. Additionally, histamine produced a significant stimulation of phosphoinositide hydrolysis as measured by [3H]inositol monophosphate accumulation, although its extent was far less than that produced by carbachol. The phosphoinositide response to histamine was blocked by chlorpheniramine. These data suggest that H1- and H2-receptors coexist in rabbit ventricles. Stimulation of H1- and H2-receptors with histamine independently sets off the biochemical responses linked specifically to the respective subtypes of histamine receptors. On the other hand, the inotropic and electrophysiological responses to histamine are governed predominantly by H1- and H2-receptors, respectively, and this results in an apparent restriction of the expression of the responses mediated by another subtype.

Interleukin-2 (IL-2) is recognized as a major activating signal for human natural killer (NK) cells. The presence of monocytes alters NK cell responsiveness to IL-2. Thus, while IL-2 effectively augments NK cell cytotoxicity (NKCC) in monocyte-depleted NK effector cells, it is relatively ineffective or even suppressive for NK cells in monocyte-containing, NK-cell-enriched mononuclear cell fractions. Here we report that concomitant treatment with IL-2 and the biogenic amine histamine synergistically augmented NKCC against K562 and Daudi target cells of CD3-/CD16+ human NK cells in the presence but not in the absence of monocytes. Addition of peripheral-blood monocytes, recovered by countercurrent centrifugal elutriation, to purified NK cells abrogated IL-2 induced NK cell activation, reconstituted the synergistic, NK-activating effects of histamine and IL-2, and strongly reduced baseline NKCC. The effects of histamine on baseline NKCC and on NK cell responsiveness to IL-2 were related to counteraction of monocyte-mediated NK cell suppression. By contrast, histamine did not affect baseline or IL-2-induced NKCC in mixtures of NK cells and monocytes when the latter cells were recovered after adherence. The effect of histamine on NK cell responsiveness to IL-2 was mediated by H2-type histamine receptors, as judged by mimicry exerted by the specific H2 receptor agonist dimaprit, but not by an H2-receptor-inactive derivative of this compound, N-methyldimaprit, and blocking by the H2 receptor antagonist ranitidine. Experiments in which monocytes and nonadherent NK cells were separately pretreated with ranitidine prior to histamine treatment suggested that NK-regulatory effects of histamine were mediated by H2 receptors on monocytes. Our data suggest that histamine may provide an important signal in the regulation of NK cell responsiveness to IL-2.

Guinea-pig duodenum contracted by histamine or by acetylcholine was relaxed dose-dependently by a series of H2-receptor selective agonists namely dimaprit, impromidine, clonidine and tolazoline. This relaxation was not neurally mediated since it was not modified by tetrodotoxin nor was it exerted through sympathetic receptors because it was not modified by pretreatment with propranolol or phentolamine. Apparently it was connected with the H2-receptor stimulation more than to peculiarities of the single compounds. However a series of H2-blocker (metiamide, cimetidine, ranitidine or oxmetidine) were unable to counteract the effect of the H2-agonists or the relaxant effect of histamine in the presence of chlorpheniramine. This peculiar situation seems to indicate the existence of anomalous H2-receptors, susceptible to the action of the agonists by not to that of the antagonists.

1 In the rat the decrease in blood pressure caused by histamine involves activation of both H1- and H2-receptors. Since arterial pressure measurements alone do not permit the separation of responses into cardiac and vascular components, the following experiments were undertaken to study vascular histamine receptors. 2 Vascular responses were studied in the autoperfused hindquarters of anaesthetized rats. Intra-arterial histamine caused vasodilatation which was only partially attenuated by treatment with mepyramine, an H1-receptor antagonist. Treatment with metiamide, the H2-receptor antagonist, did not affect vasodilatation caused by histamine but did attenuate vasodilatation which persisted after mepyramine. 3 Intra-arterial 4-methylhistamine, an H2-receptor agonist, caused vasodilatation which was reduced by metiamide. The H1-receptor agonist, 2-(2-pyridyl)ethylamine also caused vasodilatation which was blocked by mepyramine. 4 It is concluded that in the rat, histamine causes vasodilatation mediated by both H1- and H2-receptors.

Human blood leucocytes were tested for their capacity to bind histamine coupled as a rabbit serum albumin conjugate (H-RSA) to formalized ox red cells. The percentage of rosette-forming target cells was directly related to the concentration of erythrocyte-bound H-RSA. Under optimal experimental conditions the average number of rosettes was 52% for monocytes, 3 for lymphocytes, 25% for neutrophils and 59% for eosinophils. Free histamine partially inhibited rosette formation by blood monocytes in a dose-dependent fashion from 10-3 to 10-5 mol/l, and complete inhibition was achieved by the H-RSA conjugate. In contrast, three amines chemically related to histamine, L-histidine, imidazoleacetic acid and N-acetylhistamine, had no inhibitory effect. The histamine H1 antagonists, mepyramine and chlorpheniramine, and the H1 receptor agonist, 2-(2-aminoethyl)-thiazole, all inhibited rosette formation by blood monocytes in a dose-dependent fashion. However, the H2 receptor antagonists, burimamide and metiamide, and the H2 receptor agonists, Dimaprit and 4-methyl-histamine, were inactive. There was no statistical difference in the percentage of histamine rosettes for monocytes. lymphocytes, neutrophils or eosinophils between atopic and non-atopic individuals.

The activity of H1 and H2 histaminergic receptors was studied in aortic strips taken from young (6 weeks) and mature (7-8 months) rabbits. H1-mediated contractile activity was similar in both age groups, but H2 receptor relaxant activity was greatly diminished in mature rabbits. H2 receptor activity was evaluated with two experimental approaches: its modifying effect on blockade of H1 receptors by diphenhydramine (DPN), and its capacity to directly relax precontracted strips. Schild plot evaluation of DPN blockade revealed that the slope of the plot was below 1.0 in strips from young rabbits (0.77), but not in strips from mature rabbits (0.94). Propranolol pretreatment did not increase the Schild plot slope (0.66) of young aortic strips, but metiamide pretreatment did (0.92). Metiamide treatment did not further in crease slope of mature strips (0.95). When the slopes of the plots were near 1.0, as in the mature and metiamide-treated mature and young strips, the pA2 of DPN was very close (7.51, 7.70, and 7.65). Lost H2 receptor activity in maturity was confirmed by relaxing norepinephrine-precontracted strips with histamine or dimaprit. Histamine-induced relaxation of precontracted strips was slightly diminished in mature strips, while the relaxing activity of dimaprit was greatly reduced in mature tissue. The same strips relaxed vigorously when exposed to nitroglycerin or NaNO2, demonstrating that the strips were capable of relaxing. Therefore, it appears that H2 receptor activity in rabbit aorta is greatly diminished as the animal matures.

Histamine, 2-(2-pyridyl)ethylamine (PEA), a specific H1 receptor agonist, and 4-methylhistamine (4-MH), a specific H2 receptor agonist, produced a dose-dependent contraction of estrogen-primed guinea pig uterus and taenia coli. Mepyramine (10(-7) M), a specific H1 receptor antagonist, competitively blocked the responses to histamine and PEA in both the preparations. Metiamide (10(-6) M), a specific H2 receptor antagonist, inhibited the responses to histamine and 4-MH in the guinea pig uterus and taenia coli. Our data suggest the presence of both H1 and H2 receptors in the guinea pig uterus and taenia coli. Both receptors appear to be excitatory in nature.

The chemical tools that could be used to examine the function of histamine in the brain are considered together with the evidence linking histamine specifically with the hypothalamus. The distribution of histamine and the enzymes responsible for its synthesis and metabolism is consistent with there being both mast cells and histaminergic nerve terminals within the hypothalamus. Iontophoresis, mepyramine binding and histamine-stimulated adenylate cyclase studies suggest that both histamine H1- and H2- receptors are present in the hypothalamus. In addition, intracerebroventricularly injected histamine receptor agonists and antagonists affect many functions associated with the hypothalamus such as cardiovascular control, food intake, body temperature control, and pituitary hormones whose release is mediated via the hypothalamus, such as corticotropin, growth hormone, thyroid stimulating hormone, prolactin, gonadotropins and vasopressin. However, only in the case of thyroliberin release, prolactin release, body fluid control and blood pressure control is there evidence yet that such effects are mediated via histamine receptors actually in the hypothalamus. The effects of enzyme inhibitors suggest endogenous histamine may be involved in the physiological control of thyroid stimulating hormone, growth hormone and blood pressure, and the effects of receptor antagonists support a role for endogenous histamine in prolactin control. Otherwise, there is little evidence for a physiological role for endogenous, as against exogenous, histamine whether it be from histaminergic terminals or mast cells. In addition, few studies have tried to distinguish possible effects on presynaptic receptors, postsynaptic receptors, hypothalamic blood vessels or the hypophyseal portal blood vessels. It is concluded that although there is good evidence now linking histamine and the hypothalamus more specific studies are required, for instance using microinjection or in vitro techniques and the more specific chemical tools now available, to enable a clearer understanding of the physiological role of histamine in the hypothalamus.

In order to study whether both histamine H1- and H2-receptors are present in the pig mesenteric vascular bed, natural histamine, 2-(2-pyridyl) ethylamine and 4-methylhistamine, as well as mepyramine and metiamide, were infused directly into the superior mesenteric artery. The results indicate that histamine H1- and H2-receptors, both inducing vasodilation, are present in the mesenteric circulation of the pig. Jejunal motility proved to be influenced by H1-receptor stimulation only.

Ten normal human volunteers participated in a two-part study of H2-receptor activity in the ocular surface. Dimethylaminopropylisothiourea (trivial name, dimaprit dihydrochloride), a highly selective H2-receptor agonist, produced vasodilation without itch. Pretreatment with the H2-receptor antagonist, cimetidine, significantly blocked the vasodilatory effect of dimethylaminopropylisothiourea, whereas pretreatment with the H1-receptor antagonist, antazoline phosphate, did not. We conclude that H2-receptors are present in the human ocular surface.

The Kd-values of some histamine H2-active compounds, obtained from radio-ligand-binding studies on a homogenate of the guinea-pig cerebral cortex with 3H-tiotidine as the labelled H2-ligand, were compared with the pA2/pD2-value of these compounds on the guinea-pig right atrium and guinea-pig isolated gastric fundus. A good correlation was found between the pKd of the H2-antagonists and their pA2 on the guinea-pig right atrium. A much poorer correlation however was obtained between the pKd of the agonists on the cerebral cortex and their pD2-values on the guinea-pig right atrium and the gastric fundus. This poor correlation between true affinity and H2-activity of the agonists might be explained by spare receptors as a much better correlation was obtained between pKd and pD2 of partial agonists.

Twelve of 17 patients with histiocytosis-X were immunologically abnormal, as shown by the presence of circulating lymphocytes spontaneously cytotoxic to cultured human fibroblasts or of antibody to autologous erythrocytes. The patients also had a notable lack of histamine H2 surface receptors on their T lymphocytes, suggesting a suppressor-cell deficiency. The lymphocyte abnormalities were reversed in vitro after incubation in a crude extract of calf thymus gland, and therefore all 17 patients were treated with daily intramuscular injections of this extract. With this therapy, 10 patients entered complete remission -- a response at least as good as that observed in historical controls treated with chemotherapy. A positive clinical response was associated with an increase in the number of T-cell histamine H2 receptors to normal levels and with correction of the other immunologic abnormalities. The results of this preliminary study justify a larger prospective clinical trial of thymic extract and further investigation of the immunoregulatory mechanisms in histiocytosis-X.

Twelve to 30% histamine receptor bearing cells were detectable in the peripheral blood mononuclear cells of healthy tuberculin sensitive individuals. The number of binding sites per cell ranged from 2.1 X 10(4) to 5.08 X 10(4) (mean 2.5 X 10(4)) with an affinity ranging from 2.5 X 10(-6) M to 10.9 X 10(-6) M (mean 3.6 X 10(-6) M). The histamine receptors on these cells were found to be of H2 type as indicated by the abrogation of binding of 3H-histamine by cimetidine. It was further confirmed that histamine receptor bearing cells in the peripheral blood belonged to a T cell subset which formed rosettes with AET treated sheep erythrocytes and had receptors for Fc portion of IgG and phenotype markers of T3 and T8. Deletion of such cells by means of affinity chromatography on histamine bound Sepharose columns, led to enhanced antigen induced lymphoproliferation indicating the suppressor nature of these T cells.

The effect of cimetidine on basal and histamine-induced PTH secretion was tested using single cell suspensions obtained from (a) primary parathyroid adenomas, and (b) secondary hyperplastic parathyroid tissue from patients undergoing chronic hemodialysis. The histamine-stimulated hormone secretion was dose-dependent. Cimetidine suppressed both basal and histamine-stimulated hormone secretion. Within the therapeutic range the suppressive effect was identical for adenoma and hyperplasia. Both adenomata and secondary hyperplastic glands showed a histamine H2-receptor-related response. The role of histamine in the pathogenesis of hyperparathyroidism is not quite clear so that the possible benefits of cimetidine for medical treatment of primary and secondary hyperparathyroidism will have to be proven by careful clinical trials.