Relation between pharmacological response and receptor binding with histamine blocking drugs. Irreversible antagonism of three analogues of mifentidine on right atrium and cerebral cortex of the guinea-pig

Abstrac The effects of the H₂-receptor antagonists cimetidine, ranitidine, mifentidine and three analogues of mifentidine, were studied on the spontaneously beating right atrium (H₂-antagonism) and membranes of the cerebral cortex (displacement of³H-tiotidine), both obtained from the male guinea-pig. The choice of these compounds was based on preliminary experiments in which some mifentidine analogues were shown to displace tiotidine from the H₂-receptor in a deviant manner. In the present study we investigated the relation between pharmacological response and receptor binding, also testing the degree of irreversible antagonism of these compounds in the atrium (functional) and cerebral cortex (binding) model. Our data indicate that a relation between the two different approaches for measuring the effect on the H₂-receptor can be found, although some differences emerged as well.     

Pharmacological profile of mifentidine: A novel H2-receptor antagonist

Mifentidine, a representative compound of a novel class of H₂-antagonists, has been investigated for its ability to interact with H₂-receptors and to inhibit gastric acid secretion. Affinity estimates (K _B) of mifentidine obtained fromin vitro studies on cardiac and gastric mucosal histamine (H₂) receptors were in the 20–50 nM range. Mifentidine appeared to be endowed with strong antisecretory properties against histamine-stimulated secretion in the anaesthetized rat and in the conscious dog. Distinct features of mifentidine were considerable bioavailability and duration of anti-secretory effect.     

Effect of mifentidine on peptone meal-stimulated gastric acid secretion and plasma gastrin levels in duodenal ulcer patients

Mifentidine is a new H₂-receptor antagonist with distinct characteristics of potency and long plasma half-life. The aim of this study was to evaluate the effects of mifentidine on peptone meal-stimulated gastric acid secretion. Nine duodenal ulcer patients in remission were enrolled in the study and given in double-blind and at random, on two different occasions, a single tablet of 10 or 20 mg mifentidine or placebo according to an incomplete balanced block design. Ninety min after ingestion of the drug, basal gastric secretion was collected for 30 min and volume, pH and acid output determined. Thereafter, the acid output following peptone meal-stimulation was measured for 2 h by a modified version of the intragastric titration method of Thompson and Swierczek. Plasma samples were collected for gastrin and mifentidine determinations. Basal acid output was strongly inhibited by both the low dose (–78%) and the high dose (–98%) (p<0.01). The peptone meal-stimulated acid output was reduced in a dose-dependent manner (–45% by 10 mg and –90% by 20 mg). The drug did not affect the fasting serum gastrin levels but increased, although not significantly, the gastrin response to food. The log of the area under the mifentidine plasma levels correlated linearly with total acid output (p<0.01).The results of this study indicate that mifentidine dose-dependently suppresses basal acid secretion and reduces peptone-stimulated gastric acid secretion in duodenal ulcer patients.This study was supported by a grant from Boehringer Ingelheim, Italy.     

Histamine H2-receptor agonists and antagonists on pancreatic exocrine secretion of the dog

The use of H₂-receptor agonists and antagonists allowed us to establish that histamine H₂-receptors are present in pancreatic exocrine tissue and their stimulation caused a dose-dependent increase in pancreatic juice. The fact that H₂-antagonists from one side and aminoguanidine from the other were unable to modify basal levels of pancreatic secretion, seems to minimize a role for H₂-receptors in the regulation of pancreatic secretion. On the other hand H₂-antagonists modified ceruletide-induced secretion in different ways according to the different molecules. Ranitidine strongly potentiated whereas cimetidine, oxmetidine and mifentidine slightly inhibited the effect of ceruletide. The stimulatory effect of eserine and the inhibitory effect of atropine indicate a cholinergic interference in the action of ceruletide. Therefore the potentiating effect of ranitidine may be related to its cholinomimetic action and the inhibitory effect of the other H₂-antagonists may be connected with an anticholinergic effect. However, the potentiating effect of aminoguanidine on ceruletideinduced secretion may indicate a possible role for histamine in the response to ceruletide.     

The effect of histamine on the oxidative burst of HL60 cells before and after exposure to reactive oxygen species

During an inflammation neutrophils are stimulated to produce reactive oxygen species (ROS). These ROS induce the release of histamine from mast cells, which are also present at the inflammation site. In this study dibutyryl cAMP differentiated HL60 cells are used as a model for human neutrophils. The effect of histamine on formyl-methionyl-leucyl-phenylalanine (fmlp) stimulated cells is examined. Except for histamine also an accumulation of ROS takes place at the inflammation site and we investigated if ROS can influence the response of the stimulated HL60 cells. It is found that 10^–3 M histamine can inhibit the fmlp induced superoxide anion radical production. This occurs partly via an H₂ receptor because H₂ antagonists like famotidine, mifentidine and ranitidine could partially antagonize this effect of histamine. When HL60 cells are exposed to hydrogen peroxide or hypochlorous acid (20 min), an increased fmlp response is found while the inhibiting effect of histamine remains unchanged.     

Species differences in histamine receptors in the vas deferens

Histamine, specific H₁-and H₂-receptor agonists in conjunction with specific H₁-and H₂-receptor antagonists and other types of classical antagonists were used to characterize histamine receptors in the vasa deferentia of mice, rats and guinea pigs. The H₁-receptor mediates contraction while the H₂-receptor produces inhibition. There were marked qualitative and quantitative differences in the distribution of the two types of histamine receptors in the vas deferens of different species. Results indicate that mouse and rat vas deferens contain an inhibitory H₂-receptor, but virtually no excitatory H₁-receptor. In contrast, guinea pig vas deferens contained an excitatory H₁-receptor but was essentially devoid of an inhibitory H₂-receptor. The rank order of relative potencies of various agonists as well as the calculated pA ₂ values of cimetidine in the mouse and rat vas deferens suggest that the two species probably have the same H₂-receptor. High concentrations of histamine and 2-methyl histamine have a stimulant action in the mouse and rat vas deferens which was secondary to release of endogenous noradrenaline rather than to the stimulation of an excitatory H₁-receptor.     

The Receptor Binding Domain of Botulinum Neurotoxin Serotype A (BoNT/A) Inhibits BoNT/A and BoNT/E Intoxications In Vivo

The receptor binding domain of botulinum neurotoxin (BoNT), also designated the C terminus of the heavy chain (H_C), is a promising vaccine candidate against botulism. In this study, a highly efficient expression system for the protein was developed in Escherichia coli, which provided yields that were 1 order of magnitude higher than those reported to date (350 mg H_C per liter). The product was highly immunogenic, protecting mice from a challenge with 10⁵ 50% lethal dose (LD₅₀) after a single vaccination and generating a neutralizing titer of 49.98 IU/ml after three immunizations. In addition, a single boost with H_C increased neutralizing titers by up to 1 order of magnitude in rabbits hyperimmunized against toxoid. Moreover, we demonstrate here for the first time in vivo inhibition of BoNT/A intoxication by H_C/A, presumably due to a blockade of the neurotoxin protein receptor SV2. Administration of H_C/A delayed the time to death from 10.4 to 27.3 h in mice exposed to a lethal dose of BoNT/A (P = 0.0005). Since BoNT/A and BoNT/E partially share SV2 isoforms as their protein receptors, the ability of H_C/A to cross-inhibit BoNT/E intoxication was evaluated. The administration of H_C/A together with BoNT/E led to 50% survival and significantly delayed the time to death for the nonsurviving mice (P = 0.003). Furthermore, a combination of H_C/A and a subprotective dose of antitoxin E fully protected mice against 850 mouse LD₅₀ of BoNT/E, suggesting complementary mechanisms of protection consisting of toxin neutralization by antibodies and receptor blocking by H_C/A.     

Characterization of idiotopes on MOPC 315 IgA using monoclonal antiidiotypic antibodies

The isologous antiidiotypic response in BALB/c mice to immunization with the DNP-binding IgA myeloma protein, MOPC 315, alters the expression of the anti-DNP antibody repertoire and confers immunity against MOPC 315 myeloma tumors. In order to characterize the idiotopes on MOPC 315 IgA which elicit this response we have isolated four monoclonal antiidiotypic antibodies (AIA), D10 (IgG_2a), A2(IgG₁), G3 (IgG_2b) and F1 (IgG_2a), produced by splenocytes of BALB/c mice immunized with MOPC 315 IgA in three independent fusion experiments. These AIA react with MOPC 315 IgA. reassociated H³¹⁵ L³¹⁵ and F³¹⁵_V but not with free H³¹⁵, L³¹⁵, V³¹⁵_H or V³¹⁵₂. In addition the AIA do not react with the closely related DNP-binding IgA myeloma protein, MOPC 460, suggesting that they are directed against private idiotopes on MOPC 315 IgA. These idiotopes can be divided into two groups. Group I, defined by D10, A2 and G3 consists of two overlapping idiotopes, one of which is related to the hapten-binding site. The two idiotopes are formed by an interaction of amino acids in H³¹⁵ and L³¹⁵. Group II defined by F1 consists of one idiotope which is related to the hapten-binding site. This idiotope is comprised of an aminoacid sequence on H³¹⁵ which requires an interaction with either L³¹⁵ or L⁴⁶⁰ for expression. A2 and G3 react identically with the same idiotope but were derived from two independent fusion experiments. This indicates an identity of AIA clonotypes among individual mice and suggests that the isologous AIA response to MOPC 315 IgA is restricted.     

Histamine-induced inhibition of lymphocyte proliferation and lysosomal enzyme release from polymorphs may not be mediated via H1- or H2-receptors

Histamine, selective histamine H₁- and H₂-receptor agonists, and chemical analogues of these compounds lacking activity at histamine receptors, were tested as inhibitors of phytohaemagglutinin-induced human lymphocyte proliferation and zymosan-induced release of lysosomal enzymes from human polymorphs. No correlation was found between their inhibitory potency in these systems and their relative activity at histamine H₁- or H₂-receptors.     

Unexpected partial H1-receptor agonism of imidazole-type histamine H3-receptor antagonists lacking a basic side chain

Objective and design:The putative partial H₁-receptor agonism of some H₃-receptor antagonists belonging to the proxifan series was characterized in a functional in-vitro assay using guinea-pig ileum. Methods:Whole segments of guinea-pig ileum were mounted in Tyrode’s solution under isotonic conditions in the presence of atropine (10^-7 M) and were cumulatively treated with histamine as an internal reference. After washout, the putative H₁-receptor agonists were added cumulatively to determine agonist potency (pEC₅₀) and intrinsic activity (E_max) relative to histamine. Maximal or supramaximal concentrations of partial agonists, or sufficient concentrations of H₁-receptor antagonists were incubated for 3–15 min prior to construction of a second concentration-effect curve to histamine in order to calculate partial agonist or antagonist affinity for the H₁ receptor (pK_P or pA₂ value, respectively). Results:Several analogues of FUB 372 displayed low H₁-receptor affinities (pA₂ or pKP 4.2–5.5) except for a methyl benzoate derivative (pA₂ = 6.81, Schild plot slope unity). FUB 372, four ortho-substituted derivatives (R = F, CH₃, OCH₃, CF₃), and ciproxifan were weak contractile agents (E _max 9–38%, pEC₅₀ 4.73–5.68, histamine: 6.70) susceptible to antagonism by the H₁-antihistaminergic drug mepyramine (2·10^-9–10^-7 M). Agonist potency and H₁-receptor affinity of these compounds did not correlate with the data of a set of H₁-histaminergic 2-phenylhistamines bearing the same substituents. Conclusions:A specific subset of proxifans related to FUB 372 and ciproxifan represent a unique type of H₁-receptor agonists lacking a basic side chain.     

Bronchial Effects of Some Prostaglandin E and F Analogues

The effects of some analogues of PGE₁, PGE₂ and PGF_2α, rendered less accessible to the action of prostaglandin dehydrogenase by having methyl groups at carbons 15 and/or 16, or a phenyl group at carbon 17, on the tracheobronchial insufflation pressure in guinea pigs and on the tone of isolated human bronchi were investigated. Regardless of route of administration, i.v. injection or aerosol administration, PGE₁,16,16-dimethyl-PGE₁, PGE₂, the methyl esters of 15(R)15-methyl-PGE₂ and 15(S)15-methyl-PGE₂, 16,16-dimethyl-PGE₂ and its methyl ester, and 17-phenyl PGE₂ all produced a dose-dependent inhibition of the histamine-induced increase in insufflation pressure and a fall in systemic blood pressure in the anesthetized guinea pig. Although the duration of action of the PGE-analogues was longer than that of the parent compounds, none of them was more potent with regard to the peak effect produced on insufflation pressure. Of the PGF_2α analogues studied, 16,16-dimethyl-PGF_2α was the most potent compound, in decreasing rank order followed by 15(S)15-methyl-PGF_2α, 17-phenyl-PGF_2α and PGF_2α, in eliciting an increase in insufflation pressure on i.v. injection. On aerosol administration, only 16,16-dimethyl-PGF_2α compound was more potent than PGF_2α On isolated human bronchi, PGE₁ and PGE₂ were consistently relaxant, although in some expts. the relation to PGE₂ was followed by constriction. The 16,16-dimethyl analogues of PGE₁ and PGE₂ were consistently bronchoconstrictor whereas the effects of the other PGE–analogues were weak and inconsistent. In comparison with the bronchorelaxant β₂-adrenoceptor stimulating compounds, the PGEs and PGE-analogues studied do not have any outstanding features and may even imply a risk in clinical practice.     

Mutation of alkyl hydroperoxide reductase gene ahpC of Xanthomonas oryzae pv. oryzae affects hydrogen peroxide accumulation during the rice–pathogen interaction

Hydrogen peroxide (H₂O₂) is usually generated by normal aerobic respiration of pathogens and by the host defense response during plant–pathogen interactions. In this study, histochemical localization of H₂O₂ accumulation in rice inoculated with the wild-type strain (PXO99^A) and the gene deletion mutant (ΔahpC) of alkyl hydroperoxide reductase subunit C (AhpC) of Xanthomonas oryzae pv. oryzae (Xoo), the bacterial blight pathogen of rice, was analyzed. The ΔahpC mutant displayed a significant decrease in endogenous H₂O₂ accumulation which was induced by the compensatory increase in H₂O₂ scavenging activity. The change in the bacterial endogenous H₂O₂ level affected the total amount of H₂O₂ accumulation during the interaction with rice plants. These results suggested that Xoo contributes to H₂O₂ accumulation in rice in a compatible interaction, and pathogen-driving H₂O₂ is in association with cell collapse of rice.     

Synthesis of non-nucleotide ATP analogues and characterization of their chemomechanical interaction with muscle fibres

Summary To probe the substrate requirements for the actomyosin chemomechanical interaction, the effects of a series of eight new non-nucleotide ATP analogues on actomyosin-catalysed hydrolysis rates and on fibre mechanics have been investigated. These analogues have substitutions of new functional groups at the 2- and 4- positions of the ATP analogues, 2-[(4-azido-2-nitrophenyl)amino]ethyl triphosphate (NANTP), and 3-[(4-nitrophenyl)amino]propyl triphosphate (PrNANTP). Previous work has shown NANTP but not PrNANTP will support active tension and shortening in skinned muscle fibres in a manner almost identical to ATP. Here all 2- and 4- phenyl substituted analogues had myosin subfragment 1 (S1) NTPase hydrolysis rates higher than ATP and the rates were stimulated by addition of actin. In general, the replacement of the 4-azido group of NANTP with-H,-NO₂ or-NH₂ had small effects on fibre mechanics while replacement of 2-NO₂ group with-H or-NH₂ dramatically lowered the ability of the new analogues to support active tension and shortening. All PrNANTP-based analogues were ineffective in supporting active tension or shortening. We found no correlation between S1 or actoS1 NTPase rates and any mechanical parameters. However, for all analogues there was a strong correlation between the maximal velocity of shortening (V _max) and isometric tension (P _o). A three-state, chemomechanical model is proposed in which the analogues effect the transition rate into a strongly-bound, force-producing crossbridge state to account for this correlation. These studies identify 2-[(2-nitrophenyl)amino]ethyl triposphate as the chemically simplest ATP analogue which closely mimics the effect of ATP in skinned muscle fibres.     

Continuous recording of intrapulmonary “Compressed air” as a sensitive noninvasive method of measuring bronchial obstruction in guinea pigs

The method presented is based on whole-body plethysmography. The apparatus consisted of two chambers (a=respiratory, b-body chamber) separated by a tight water-filled rubber cuff which was fixed around the head of the animal. Experiments were performed under constant gas conditions: temperature 30°C, 100% relative humidity, the volumes of the two chamber being identical. Volume changes in the chamber (V _a, V _b) were recorded continuously by means of pressure transducers. Respiratory flow was calculated by differentiation of V _a with respect to time. The three parameters V _a, V _b and respiratory flow allowed the calculation of breathing frequency, inspiration/expiration ratio, (peak) expiratory flow and specific airway conductance. In addition we describe a new parameter indicating bronchial obstruction: a graphical plot of V _b against V _a produces a closed loop, the area of which reflects the degree of airway obstruction, and we read off the parameter we term compressed air from this graph. In our hands this parameter was more than ten times as sensitive as other measures of bronchial obstruction. Using this new technique we have carried out pharmacological studies with eicosatetraynoic acid (ETYA), 2-aminomethyl 4-t-butyl-6-iodophenol (MK 447=radical scavenger), the histamine₁ antagonist elemastine and the histamine₂ antagonist cimetidine. In allergen-tested animals we observed mild protective effects of ETYA when given as an aerosol (3 mg) and pronounced effects of MK 447 (4 mg i.p.). Combined H₁H₂-antagonism was much more effective in preventing allergen-induced bronchial obstruction than H₁-antagonism alone.Supported by Deutsche Forschungsgemeinschaft (Do 240/1)     

Assessment of ferrocytochrome C oxidation by hydrogen peroxide

The reduction of ferricytochrome C is commonly employed for the quantitation of O ₂ ^– . H₂O₂ arising from the dismutation of O ₂ ^– is capable of oxidizing ferrocytochrome C. In order to assess whether this may interfere with O ₂ ^– quantitation, the amount of H₂O₂ required for the oxidation of ferrocytochrome C was determined. While H₂O₂ concentrations below 10^–5 M were ineffective, one half of the reduced cytochrome was oxidized by 5×10^–5 M H₂O₂ within 15 min. H₂O₂ in the concentration range at which ferrocytochrome C is oxidized is generated upon interaction of hypoxanthine with xanthine oxidase and upon stimulation of human polymorphonuclear neutrophilic granulocytes by phorbol myristate acetate or the phagocytosis of opsonized zymosan. It is suggested that O ₂ ^– quantitation by cytochrome C reduction is routinely performed in the presence of catalase.     

Copolyesteramides, 9. Random 6-iminohexanoyl/12-oxydodecanoyl copolyesteramides

Random copolyesteramides composed of NH(CH₂)₅CO (6A) and O(CH₂)₁₁CO (12E) units were prepared by co-polymerization/condensation of 6-hexanolactam with 12-hydroxydodecanoic acid. Lactam elimination during the reactions limited the attainable 6A content to ca. 70 mol-%. The properties of the materials differ markedly from those of the isomeric O(CH₂)₅CO/NH(CH₂)₁₁CO random copolymers. Those with up to 20 mol-% 6A units are crystalline and essentially modified 12E polymers. Thereafter, up to ca. 55 mol-% 6A, the materials were of an intermediate, relatively homogeneous phase character, a discrete polyamide phase appearing incipiently only at still higher 6A contents. The random nature of the copolymers was confirmed by ¹³C NMR spectroscopy, and IR examination showed the prevalence of amide-ester hydrogen bonding at lower 6A contents together with a degree of intramolecular sub-crystalline order in the 12E component over the range from 20–60 mol-% 6A. It is suggested that the copolymer texture in this range is largely controlled by the preferred conformation of the (CH₂)₁₁ units of the ester component. Some properties, including the unit cell parameters, of the little-known 12E polyester, [poly(12-oxydodecanoyl)], are reported.     

Comparison of the central nervous system effects produce by six H1-receptor antagonists

Background A comprehensive comparative study of the central nervous system (CNS) properties of newer H₁-receptor antagonists is needed. Objective Our objective was to investigate the central nervous system eifects of u single manufacturer's recommended dose of six H₁-receptor antagonists, using appropriate controls. Methods Fifteen healthy subjects received astemizole 10mg, cetirizine 10mg, ketotifen 2mg, loratadine 10 mg, terfenadine 60mg, diphenhydramine 50mg or placebo. Before and 2-1.5 h after dosing, cognitive function was assessed using the P300-event-related potential, somnolence was assessed using a subjective score, and histamine skin tests were performed. Results In rank order from least to greatest effect on the P300 latency, the medications were: terfenadine, placebo, cetirizine, ketotifen, loratadine, astemizole and diphenhydramine. Only diphenhydramine increased the P300 latency significantly compared with baseline and placebo. Subjective somnolence was significantly greater than baseline and placebo after cetirizine, ketotifen and diphenhydramine. All the H₁-receptor antagonists suppressed the histamine-induced weal significantly compared with baseline. Conclusions The H₁-receptor antagonists tested affected cognitive functioning and somnolence to different extents, although all produced satisfactory peripheral H₁-blockade.     

Protective and inactivating effects of neutrophil myeloperoxidase on C1q activity

This study investigated the interaction between neutrophil myeloperoxidase (MPO) and the C1q component of the complement system. Using a dot-spot assay, MPO was found to bind to C1q in a dose-dependent manner. The specificity of this reaction was proved by the inhibitory effect of F(ab')2 antibodies to C1q and by the inability of MPO to bind to Clr, Cls and IgG. The interaction between MPO and C1q did not influence the enzymatic activity of the peroxidase but resulted in a more stable C1q as assessed by hemolytic assay for C1q. The protective effect of MPO on C1q did not require the presence of H₂O₂ in the reaction mixture nor was it inhibited by sodium azide, whereas it was abolished by heating the peroxidase. Lactoferrin and lysozyme, unlike MPO, were ineffective in protecting C1q from functional decay. Addition of H₂O₂ and chloride to MPO and C1q led to a complete inactivation of C1q, which could not be induced by H₂O₂ alone. The hypochlorite, which is known to be generated during the reaction of MPO with H₂O₂ and chloride, exhibited a similar inactivating effect on C1q, which was prevented by an external source of methionine.     

The pressor activity of burimamide: A relationship between chemical constitution and pressor activity of burimamide and related histamine H2-receptor antagonists

Burimamide, a histamine H₂-receptor antagonist, has been shown to cause pressor responses in pithed rats. The response can be prevented by prior removal of the adrenal glands or by pretreatment with the -adrenoceptor antagonist, phentolamine, 5 mg/kg, suggesting that the pressor response to burimamide is due to release of catecholamines from the adrenal glands.The pressor activity of burimamide has been compared with that of metiamide and two close chemical analogues, methylburimamide and thiaburimamide, in order to identify which chemical features of the compounds are necessary for this activity. Methylburimamide was the most potent pressor agent, followed by burimamide, metiamide and thiaburimamide. The pressor effects (and presumably catecholamine-releasing activities) appear to be related to the basicities of the compounds.We conclude that the release of catecholamines by these histamine H₂-receptor antagonists is probably due to their cationic (imidazolium) forms.     

Structural requirements of imidazole compounds to be inhibitors or activators of histamine methyltransferase: Investigation of histamine analogues and H2-receptor antagonists

The influence of imidazole compounds (histamine analogues and H₂-receptor antagonists) and of the specific histamine H₂-receptor agonist dimaprit on histamine methyltransferase (HMT) from pig gastric mucosa was investigated.By their effect on HMT two groups of substituted imidazole compounds could be differentiated. Some were pure inhibitors of the enzyme, whereas others were inhibitors only in high concentrations (>10^–3 M) and activators of the enzyme in low concentrations. The strongest inhibitor of all the histamine analogues tested was 2-methylhistamine (I.D.₅₀=0.6×10^–4 M), whereas the strongest activation was exerted by 4-[(2-amino-ethylmercapto)-methyl]-5-methylimidazole (57% increase of enzymic activity at 10^–4 M concentration). From the group of histamine H₂-receptor antagonists only burimamide was an inhibitor (I.D.₅₀=1.6×10^–4 M) whereas metiamide and cimetidine belonged to the strongest activators of the enzyme (179% enzymic activity at 10^–4 M concentration of metiamide).The strongest activator of all the substances tested in this series of compounds, however, was the non-imidazole compound dimaprit, which increased enzymic activity by 86% in as small a concentration as 10^–5 M.For substituted imidazole ring systems an attempt is made to evaluate the structural requirements of the single compound to classify it as a pure inhibitor or a concentration-dependent inhibitor/activator of HMT.Dedicated to Prof. Dr Dr E. Werle () on the occasion of his 75th birthday.Supported by grant Lo 199/7 from Deutsche Forschungsgemeinschaft.Presented at the Sixth Annual Meeting of the European Branch of the Histamine Club, held in London, April 20–22, 1977.