Effects of histamine H2-antagonists on pre- and post-natal development in the rat

Inflammation Research -     

Modulation of IgE-mediated histamine release from human leukocytes by a new class of histamine H2-agonists

A new class of phenyl (pyridylalcyl) guanidines, acting as potent histamine H₂-agonists, inhibits IgE-mediated human basophil histamine release in a nanomolar range. IC₃₀-level of three substitutes of this group (arpromidine, BUA-75, and FRA-19) were found to be 0.02, 0.015 and 0.008 M. The inhibition appeared with a fast onset (plateau after 10 min. preincubation) and claimed its maximum (60±2.9%, 63±1.8%, and 61±3.1%,n=7) with 10 M of the compounds. H₂-mediated inhibition was totally blocked by 10 M famotidine, a potent histamine H₂-antagonist. The amount of anti-IgE or antigen for the initiation of the immunological release influenced the strength of inhibition of H₂-agonist FRA-19 (p<0.05). Combined preincubation of FRA-19 with zardaverine, a cAMP-specific phosphodiesterase III/IV inhibitor, produced a synergistical inhibitory effect of leukocyte histamine release, which might explained by their different sites of action on intracellular cAMP levels. The capability of histamine to inhibit its own release is mediated by H₂-receptors exclusively. New, potent H₂-receptor stimulating compounds with positive inotropic effects possess additional potent anti-allergic properties.This work was supported by grant K1 622/1-1 from the Deutsche Forschungsgemeinschaft.     

Autoradiographic localization of binding sites for [3H]histamine and H1- and H2-antagonists on cultured neurones and glial cells

By means of autoradiography we have studied the cellular localization of binding of [3H]histamine and H1- and H2-antagonists in explant cultures of rat cerebellum, brain stem and spinal cord. In brain stem and spinal cord cultures, a relatively great number of neurones revealed binding sites for [3H]histamine and to a lesser extent also for the H1-antagonist [3H]pyrilamine and for the H2-antagonist [3H]tiotidine. In contrast, only a small number of labelled neurones was found in cerebellar cultures. The intensity of labelling was usually much stronger for [3H]histamine than for its antagonists, suggesting that binding sites for histamine might reflect both H1- and H2-receptors. Glial cells also showed binding sites for [3H]histamine and the H1- and H2-antagonists, the number of labelled astrocytes by these radioligands was, however, smaller than that observed with [3H]noradrenaline and alpha- and beta-adrenergic antagonists. It is suggested that in addition to alpha- and beta-adrenoceptors, glial cells also possess receptors for histamine.     

Action of histamine and of some H2-antagonists on gastric secretion ‘in vitro’

The effect of histamine and of some H₂-antagonists on isolated gastric mucosal preparation from immature (14–18 days) rats, was investigated. Basal secretion varied, in our experimental conditions, between 1.06 and 3.54 mol cm^–2 h^–1, reaching higher values (approximately 4.6 mol cm^–2 h^–1) only in a small percentage of animals (10%). Histamine exerted a concentration-dependent stimulation of acid secretion in concentrations varying between 2×10^–6 and 1.6×10^–4 M. the response to histamine was competitively antagonized by ranitidine (pA₂ value=6.78) and by 4(5)-(4-isopropylaminomethyleniminophenyl) imidazole (compound marked DA 4577) (pA₂ value=7.37). Oxmetidine acted as a competitive antagonist only for concentrations as low as 10^–8 M; higher concentrations (10^–7 and 10^–6 M) determined a non-competitive inhibition. Ranitidine and compound marked DA 4577 did not affect basal secretion up to concentrations of 3×10^–4 M. On the contrary oxmetidine exerted a concentration-dependent inhibition starting from 10^–5 M. Since in our experimental conditions the role of calcium ions in the regulation of basal secretion could not be established, the mechanism of action of oxmetidine was not completely clarified, even if an interference in the utilization of calcium ions may be suggested. In any case it is deemed of interest that this H₂-antagonist was the only compound capable of inducing a reversible complete inhibition of basal acid secretion (only KSCN, in very high concentrations, had a similar behaviour).     

Selective disappearance of histamine H2-receptor activity in the human gastric cancer cell line HGT-1 after short-term or chronic treatment by histamine or its H2-antagonists

Homologous loss of histamine H₂-receptor activity (cAMP generation) was observed after short-term (10–20 min) or chronic treatment (6 days) of cultured HGT-1 cells with histamine (desensitization) or the H₂-receptor antagonist SKF 93479. This inactivation process was not observed when HGT-1 cells were exposed to the classical H₂-antihistamine cimetidine.The data show: (1) that the compound SKF 93479 has a very prolonged inhibitory action on histamine receptor activity, suggesting an irreversible interaction between the antagonist and the receptor; (2) that cimetidine is a reversible H₂-receptor antagonist which can be removed without changing the the efficacy and the potency of histamine on gastric cells; (3) that the H₂-receptor antagonists cimetidine and SKF 93479 specifically block histamine H₂-receptor activity in HGT-1 cells since cAMP generation induced by other hormones such as vasoactive intestinal peptide (VIP), glucagon or gastric inhibitory peptide (GIP) was unchanged after treatment; (4) the first evidence for time-dependent (half-life: 20 min) desensitization of gastric H₂-receptors.     

Effect of nitrendipine on histamine release from human basophil leukocytes

The effect of the new calcium antagonist nitrendipine on in vitro basophil activation was evaluated in 10 subjects. The histamine release induced by calcium ionophore A23187, f-met peptide and anti-IgE was inhibited, in a dose-dependent fashion, by nitrendipine in the concentration range of 1-100 microM. The activity of this calcium antagonist seems complex and related to an interference with calcium at multiple sites. At concentrations higher than 200 microM, nitrendipine causes histamine release from basophil leukocytes. This histamine secretion is likely to be due to a cytotoxic effect, since it is associated with an increase in LDH levels in the cell supernatant.     

Inhibitory action amlexanox on interleukin-3-induced enhancement of histamine releasability of human leukocytes]

Amlexanox, an anti-allergic drug, showed a concentration-dependent inhibition against hrIL-3-induced enhancement of in vitro histamine release from human leukocytes by anti-IgE. The significant inhibitory action of amlexanox was observed in one out of nine and six out of nine allergic subjects at concentrations of 10(-5) M and 10(-4) M, respectively. This means that the inhibitory effect of amlexanox varied from patient to patient. Post-treatment as well as simultaneous treatment with amlexanox produced an inhibitory action on the enhancing effect of hrIL-3, suggesting that hrIL-3-induced enhancement of releasability is a reversible reaction. AA-861, OKY-046, superoxide dismutase and prostaglandin E2 showed no effects on the hrIL-3-induced enhancement of histamine releasability. The inhibitory action of amlexamox to the hrIL-3-induced enhancement of histamine releasability may be a new anti-allergic mechanism, details of which remains unclear.     

The inhibition of salivary secretion by histamine H2-antagonists—a study on the cat submandibular gland

The aim of the present work was to establish whether the secretory process can be influenced by histamine H₂-receptor antagonists, burimamide and metiamide. These drugs were applied intravenously and the secretion was evoked by the electrical stimulation of the chorda tympani nerve or by carbachol (i.v.). In addition to the measurements of the flow of saliva, the blood flow through the gland was measured in some experiments. Both H₂-antagonists significantly reduced the rate of salivary secretion induced by the chorda tympani stimulation. The experiments with burimamide did not permit the calculation of dose-response relationship. From the experiments with metiamide the ED₅₀ was 4.6 μmol/kg and E_max was 30% reduction of secretion. The secretory response to carbachol was not diminished by burimamide. In addition to the effect of metiamide on salivation, the reduction of the blood flow through the gland was observed: the effect on the blood flow was significantly smaller, and slower in onset, than the effect on salivation. These results support the hypothesis that H₂-receptors are involved in the process of salivary secretion. Histamine effects on glandular elements seem to be more significant than its effect on the blood vessels.     

Ultraviolet A inhibits histamine release from human peripheral leukocytes

Irradiation of human peripheral leukocytes with ultraviolet A (UVA) induced a significant and dose-dependent reduction of anti-IgE or Ca-ionophore-stimulated histamine release without consistent influence upon C5a-induced release reactions. This effect was equally demonstrable in atopics and controls. In the presence of the radical scavenger superoxide dismutase, the UVA-induced inhibition of anti-IgE-induced histamine release was abolished. Under the conditions used, UVB exposure did not result in relevant changes of in vitro histamine release.     

The role of histamine H-receptors in the anaphylactic histamine release from human basophilic leukocytes

The effect of two recently synthetized selective histamine H2-receptor agonists on anaphylactic histamine release from human basophilic leukocytes was investigated. It was found that both agonists tested, partially inhibited histamine release induced either by antigen or by human anti-IgE. Cimetidine, the histamine H2-receptor antagonist, generally antagonized this effect. It is concluded that anaphylactic basophil histamine release can be modulated by stimulation of histamine H2-receptors.     

Complement activation requirements for histamine release from human leukocytes: influence of purified C3ahu and C5ahu on histamine release

The activation of human sera for histamine release by zymosan and anti-BSA-BSA complexes at equivalence was dose dependent and associated with a marked fall in CH50, C3 and C5 hemolytic activities. Heat-aggregated IgG, though able to fix greater than 90% of human CH50 activity and produce a lesser fall in C3 and C5 activities than zymosan and BSA-anti-BSA complexes, was unable to induce basophil histamine release. Chemically purified human C3a and C5a each caused histamine release from human basophils; C5a was more potent than C3a. In addition, neither zymosan nor BSA-anti-BSA complexes released histamine when incubated with homozygous C3-deficient serum. The addition of C3a and C5a at suboptimal concentrations produced an additive effect of histamine release.     

Bacteria-induced histamine release from human bronchoalveolar cells and blood leukocytes

Histamine release induced by Staphylococcus aureus was examined in cells obtained by bronchoalveolar lavage (BAL) in non-atopic individuals. Approximately half of the individuals responded with mediator release to the bacterium, and the release was found to be time- and concentration dependent. No difference was found between the patients who responded and those who did not respond in regard to age, sex, smoker/non-smoker, % recovery of BAL-fluid, total cell count, differential cell counts, histamine content per mast cell, or diagnoses. Also stimulation of the BAL-cells with the calcium-ionophore A23187 resulted in histamine release. S. aureus-induced histamine release from basophils was examined in leukocyte suspensions obtained from the same individuals, and in all experiments release was found. The dose-response curves were similar to those obtained with BAL cells. The bacteria-induced mediator release from superficially lying cells in the airways epithelium might be of importance for the precipitation or exacerbation of bronchial asthma in respiratory tract infections.     

IgG4 and release of histamine from human peripheral blood leukocytes

Allergen-specific IgG4 was found in the sera from many normal, nonallergic individuals. Basophil leukocytes from donors with IgG4 antibodies to an allergen, but without IgE antibodies to the same allergen, did not release histamine when challenged with this allergen. In some cases, anti-IgG4 antiserum induced a release of histamine from the leukocytes. However, these cells also release histamine after incubation with normal rabbit serum or normal sheep serum. It is concluded that the IgG4-RAST cannot be used for the detection of IgG short-term sensitizing antibodies.     

Histamine release from human peripheral blood leukocytes analyzed by histamine radioimmunoassay

Histamine release from human peripheral blood leukocytes, afterin vitro challenge with allergen extracts, is usually measured by fluorometry. In the present study we compared the results of the automated fluorometric histamine assay (Siraganian) with those of the Immunotech histamine radioimmunoassay. Histamine release dose — response curves obtained after histamine measurement by both methods were superimposable.     

Release of histamine from human leukocytes by one preparation of IgG oligomers

In preliminary experiments aimed at investigating the effect of covalently cross-linked human myeloma subclass proteins on histamine release from human leukocytes, we observed one preparation (designated here IgG-HR) made from pooled, purified immunoglobulin G, which consistently released histamine from these cells. Dimers and trimers, but not monomers isolated from columns of Sephadex G-200 and Ultrogel AcA22 following incubation of immunoglobulin G (Nordic Laboratories) with dimethyl suberimidate, released histamine from cells of all donors tested. In contrast, cells from the same donors showed variable responsiveness to dimers of IgE (prepared by similar techniques) or to anti-IgE. IgG-HR failed to release histamine from a "basophil-rich" mononuclear cell preparation depleted of most of the erythrocytes, platelets, neutrophils and eosinophils by centrifugation through a Ficoll-Hypaque cushion. The data suggest that IgG-HR was releasing histamine indirectly from basophils by first interacting with another cell. IgG oligomers prepared from different sources of pooled, purified IgG failed to release histamine. Although we did not have sufficient IgG-HR to adequately define this releasing activity, we feel that the data represent a potentially novel, if rare, mechanism of mediator release involving basophils and another cell.     

CNS access of selected H3-antagonists: ex vivo binding study in rats

Inflammation Research -     

Augmentation of allergic histamine release from human leukocytes by nonsteroidal anti-inflammatory-analgesic agents

Augmentation of allergic histamine release in vitro with human leukocytes was produced by numerous nonsteroidal anti-inflammatory--analgesic agents, primarily the arylalkanoic and anthranilic acids. Augmentation occurred without release of histamine by the agents in the absence of the allergen (ragweed) and only under conditions of an accompanying release by the allergen. As a consequence of augmentation, less allergen was necessary to produce a given response in the presence of these agents. It is suggested that some of these agents might enhance mediator release in immediate-type hypersensitivity reactions. The same agents reported to exacerbate chronic urticaria, i.e., indomethacin, mefenamic acid, sodium salicylate, aspirin, sodium benzoate, and tartrazine, also augmented allergic histamine release. Pharmacologically mediated augmentation of mediator release from stimulated cells is suggested to be involved in the exacerbation of existing chronic urticaria by the acidic nonsteroidal anti-inflammatory-analgesic agents.