Specific binding of [3H]mepyramine to histamine H1-receptors in vascular smooth muscle membranes

The antagonist-sensitive binding of [³H]mepyramine to beef aortic membranes was as expected for binding to histamine H₁-receptors. [³H]mepyramine binds rapidly and in saturable fashion to the specific receptor sites, specific binding reaching equilibrium in 3 min at 37°CScatchard's analysis of the binding data gave a dissociation constant of 3.0 nM for the radioligand-receptor complex and maximal number of binding sites: 31 fmol/mg protein. In the competition studies histamine H₁-antagonists are more potent inhibitors of radioligand binding than H₂-antagonist. They inhibit [³H]mepyramine binding in the following order: mepyramine >triprolidine     

Characterization of coexistent histamine H1- and H2-receptor binding sites in the purified guinea pig myocardial membranes from ventricles

In the present work, we identified and characterised histamine H1-and H2-receptors in highly purified myocardial membranes isolated from female guinea pig ventricles. We determined the binding parameters for the interactions of³H-mepyramine with the histamine H1-receptor binding site and³H-tiotidine with the histamine H2-receptor binding site. Binding of both ligands in our study was saturable, reversible and of high affinity. Scatchard's analysis of the specific³H-mepyramine binding revealed the existence of high and low affinity binding sites with apparent K_D values of 0.4 nM and 4.5 nM, respectively. The density of binding sites (B_max) was 100 fmol/mg protein for the high and 466 fmol/mg protein for the low affinity binding site.³H-tiotidine binds to a single population of binding sites with a K_D of 1.0 nM and a B_max of 27 fmol/mg protein. These data suggest that both histamine H1-and H2-receptors coexist in the guinea pig myocardium with a significantly higher prevalence of the histamine H1-receptor population.     

Characterization of vascular histamine H1-receptors: Multiple affinity states of aortic histamine H1-receptor

We have shown that [³H]mepyramine labels histamine H₁-receptor-binding sites in bovine aortic membranes. Further characterization of H₁-receptors in this tissue was done by the interaction of an unlabelled histamine receptor agonist or antagonist, with the radioantagonist [³H]mepyramine-binding sites. The competition-binding assays have uncovered differences in the characteristics of the agonist/receptor interaction not shared by antagonists. Agonists interact in the heterogeneous manner with the radioantagonist-labelled sites, showing shallow competition curves with then _H 0.50–0.72, whereas antagonists were devoid of this effect (steeper slopes of the inhibition curvesn _H1). The results suggest the presence in this tissue of multiple affinity states of histamine H₁-receptor, differentiated by high and low affinity for agonists and the same affinity for antagonists.     

雌激素对血管平滑肌的作用

血管平滑肌细胞是保持血管功能完整性的重要结构和功能单位,在动脉粥样硬化、高血压、冠心病及损伤后再狭窄的发病机制中具有关键性作用。本文对雌激素通过功能性的雌激素受体调节血管平滑肌细胞的结构和功能进行综述。     

Pro-cognitive effect of a selective histamine H1-receptor agonist, 2-(3-trifluoromethylphenyl)histamine,in the rat object recognition test

Inflammation Research -     

Effects of selective histamine H3-receptor ligands on prolactin and growth hormone secretion in the rat

The effects of intracarotid (i.a.) administration of the histamine (HA) H₃-receptor agonist (R)--methyl-histamine (MeHA) and of the H₃-antagonist thioperamide, (THIO) on basal or morphine (M)-induced prolactin (PRL) and growth hormone (GH) secretion were studied in male rats. M was administered 3 h after the H₃-drugs. Neither THIO (2.5 mg/kg) nor MeHA (10 mg/kg) changed basal PRL levels and only THIO enhanced the PRL-releasing effect of M (6 mg/kg). Basal GH secretion was not modified by THIO. MeHA slightly increased GH secretion. THIO significantly decreased M-stimulated GH secretion (1 mg/kg, i.a.) and MeHA slightly increased it. These results, in agreement with previous evidence obtained after central HA administration, indicate that endogenous brain HA facilitates PRL and inhibits GH secretion.     

Studies on the mode of action of histamine H1- and H2-receptor antagonists on gastric histamine methyltransferase

Histamine methyltransferase from pig antrum mucosa was inhibited by 33 H₁-receptor antagonists, by the H₂-receptor antagonists burimamide and metiamide and by the burimamide analogue 5-methylburimamide, which did neither act on H₁-nor on H₂-receptors. Whereas all H₁-receptor blocking agents as well as metiamide and 5-methylburimamide inhibited the enzyme in a competitive manner, the type of inhibition found for burimamide was a mixture of non-competitive and uncompetitive with respect to histamine, which is similar to that one observed with 1-methylhistamine, the product of the histamine methylation reaction. Furthermore, all compounds tested — with the only exception of burimamide — activated the gastric histamine methyltransferase in lower concentrations, the most potent activator being piprinhydrinate (180% increase of the enzyme activity). This enhancement of 1-methylhistamine formation by antihistaminic drugs was not due to a true activation of the enzyme by increasingV _max, but was caused by partially abolishing the inhibition of histamine methyltransferase by so-called optimum concentrations of histamine. Two explanations were given for the different mode of action of burimamide compared with that of metiamide and the other antihistaminic drugs: (1) The change in the type of inhibition from burimamide to metiamide seemed to be due to the introduction of a methylgroup into position 5 of the imidazole ring. (2) Burimamide and 1-, 2- and 3-methylhistamine were the only compounds tested in which the imidazole nucleus was substituted at position 4, but not at position 5, and which thus probably produced substrate or product inhibition.supported by a grant of the Deutsche Forschungsgemeinschaft (Lo 199/3).     

Effects of histamine H1-receptor stimulation on coronary hemodynamics in man

Exogenous histamine in man induces significant cardiovascular effects mediated by activation of H₁ and H₂-receptors present on human heart and on coronary arteries. We studied the effects of selective H₁-receptor stimulation on human coronary hemodynamics in 10 patients undergoing cardiac catheterization. All patients were pretreated with cimetidine before the histamine infusion (0.5 g/kg/min i.v. for 5 min). Six of these patients had normal coronary arteries and four had single vessel coronary artery disease (CAD) and vasospastic angina. During the study heart rate was held constant (100 beats/min) by coronary sinus pacing. We measured mean aortic pressure (MAP), coronary sinus blood flow (CSBF), coronary vascular resistance (CVR) and myocardial oxygen consumption (MVO₂) at rest, during histamine infusion, and 10 min after the end of the infusion. During infusion, MAP decreased from 103±5 to 85±6 mmHg (p<0.02) and CVR from 1.00±0.16 to 0.81±0.14 mmHg/ml/min (p<0.05); CSBF and MVO₂ did not significantly change. All parameters returned to baseline at the end of the infusion. The response was similar in patients with normal coronary arteries and in 3 patients with CAD. Only one patient with CAD developed angina with ST segment elevation in D₃, reduction in CSBF and an increase in CVR. These results indicate that H₁-receptor stimulation in man induces significant coronary dilatation and that histamine infusion after cimetidine pretreatment is unlikely to provoke coronary spasm in patients with vasospastic angina.     

Lack of influence of histamine H1-, and H2-receptor antagonists on histamine level in rat brain

The intraperitoneal administration of three antihistaminic drugs of H1 type: mepyramine, diphenyhydramine (each 5 and 30 mg/kg) and danitracen (2 and 10 mg/kg) did not modify histamine level in the rat brain after 2 h. Histamine H2-receptor antagonists: cimetidine (25-250 microgram) and metiamide (100 microgram) given directly into the brain had no significant effect on histamine content after 1.5 h. L-histidine (0.5 g/kg i.p.) increased after 1.5 h histamine level in various experiments by 50-75% above control. All antihistaminic drugs did not change significantly histamine level in the brains of L-histidine-treated rats though a slight but consistent tendency to decrease the L-histidine effect in the group of H2-receptor blocking drugs was observed.     

The influence of histamine H1-, H2- and H3-receptor antagonists on histamine stimulated NGF release from cultured astrocytes

Inflammation Research -     

Reversal of alpha 1-receptor mediated relaxation in intestinal smooth muscle

The alpha 1-receptor agonist phenylephrine relaxed longitudinal rabbit jejunal muscle contracted in vitro by low concentrations of barium ions (1 mM). When the Ba2+ concentration was increased to 10-15 mM the response to phenylephrine was a contraction, and at Ba2+ concentrations in between the high and low range this response was biphasic--a relaxation followed by a contractile phase. The alpha 2-receptor agonist clonidine did not affect the tone of the Ba2+ contracted preparation. When the muscle preparation was contracted by Sr2+ (1-20 mM) in the presence of Ca2+ (2.5 mM), phenylephrine relaxed it, and no contractile response to phenylephrine was observed. In the absence of extracellular Ca2+, 5 mM Ba2+ caused a contraction. Under these conditions phenylephrine had no effect on the tissue tone. When Ca2+ was added in a low concentration (0.2-2 mM), phenylephrine elicited a gradually increasing contractile response. At 5 mM Ca2+ the contractile response was replaced by the normal relaxation. The contractile response to phenylephrine in the presence of 5 mM Ba2+ and 2.5 mM Ca2+ was partially blocked by low concentrations of verapamil. In higher concentrations verapamil abolished the tissue tonus completely. The contractile response to phenylephrine in the presence of 5 mM Ba2+ and 2.5 mM Ca2+ could be reverted to the normal relaxation by the addition of 20 mM Mg2+. Increasing the K+ concentration from the normal 5.9 to 62.9 mM blocked the phenylephrine-induced relaxation. No contractile response to phenylephrine occurred. It is concluded that Ba2+ could reverse the response of alpha 1 receptor stimulation in rabbit jejunum from a relaxation to a contraction and that this contractile response was dependent on the presence of Ca2+.     

Labelling of non-H1-receptor binding sites by [3H]-mepyramine on the rat liver plasma membrane

In the present study we characterized [³H]-mepyramine binding to rat liver plasma membranes. Binding of [³H]-mepyramine proved to be of high affinity (K _d =7.7±0.4 nM) and saturable, resulting in a B_max-value of 70.4±9.5 pmol/mg protein. However, displacement studies revealed that this binding site was different from other H₁-receptor systems. The two stereoisomers of chlorpheniramine were rather ineffective in displacing [³H]-mepyramine and showed a stercospecificity in favour of thel-isomer. Also several H₁-receptor agonists were not potent in displacing [³H]-mepyramine from rat liver plasma membranes. Morcover, the histamine metabolite imidazole-4-acetic acid was about as potent as the H₁-agonists, whereas imidazole was even more potent. These data strongly suggest that [³H]-mepyramine labels a non-H₁-receptor binding site on the rat liver plasma membrane.     

The effect of histamine on the smooth muscle cells of the ear artery of the rabbit

Histamine activates both H₁- and H₂-receptors in the ear artery of the rabbit. The specific action of these receptor activations on the membrane potential and the force development has been investigated by using the H₁-blocking agent mepyramine and the H₂-blocking agent cimetidine. H₁-activation depolarizes and increases force development, while H₂-activation hyperpolarizes and reduces force development. These effects on the force development can occur independently of the changes of the membrane potential. By determining the effect of histamine on tissues which were denervated with 6-hydroxydopamine it was shown that histamine exerts its effect directly on the smooth muscle cells. Na-deficiency depolarizes the smooth muscle cells, but it also reduces the changes of the membrane potential and the force development induced by H₁-stimulation. K-free medium prevents the hyperpolarizing effect of H₂-activation. As far as the ion fluxes are concerned and H₁-activation is found to induce an increased efflux of K while a simultaneous H₂-activation only reduces the increase of flux induced by H₁-activation. H₁-activation induces a release of Ca from the intracellular Ca stores, while H₂-activation inhibits this release.This work was supported by a grant of the Fonds voor Wetenschappelijk Geneeskundig Onderzoek, Belgium no. 3.0087.74     

Trophic effect of the sympathetic nervous system on vascular smooth muscle

While the vasomotor effect of the sympathetic nervous system (SNS) on the arterial wall is well recognized, its trophic function is not. It is the aim of these studies to demonstrate this all-important function as it relates to the vascular muscle. Although the exact mechanism by which sympathetic nerve impulses influence the metabolism of the vessel wall is unknown, effects of sympathectomy can be demonstrated. Several lines of evidence indicate that chronic absence of sympathetic innervation in rabbits increases collagen synthesis and decreases activity of tricarboxylic acid cycle enzymes in the vascular wall. When chemically sympathectomized rabbits were fed a 1% cholesterol dietary supplement for 80 days, the aortas of these rabbits contained significantly more cholesterol and total lipids than those from fully innervated controls in spite of insignificant differences in plasma lipids. In a subsequent series of experiments we analyzed the efficacy of the SNS in two strains of pigeons. White Carneau (WC) pigeons are known by their susceptibility to atherosclerosis of the aorta while Show Racer (SR) pigeons are not. Our results demonstrate that the abdominal aorta of WC pigeons has less sympathetic innervation and it declines faster with age than that of SR pigeons. The results of the described studies documenting the direct trophic influence of the SNS on the arterial wall are reinforced by the similarity to the vessel wall changes induced by partial sympathectomy and natural aging. Various phases of this work were done in collaboration with Drs. N. Alexander, D. Amiel, C.M. Bloor, M. Chvapil, J.D. Turner and T. Zemplenyi.     

Effects of histamine H1-receptor blockade on respiratory and cardiac manifestation of systemic anaphylaxis

Summary In vivo anaphylaxis is associated with respiratory distress and cardiovascular failure. The present investigation was designed to further characterize respiratory and cardiac anaphylactic events. In guinea pigs, sensitization was produced by subcutaneous application of ovalbumin together with Freund's adjuvant. Fourteen days after sensitization, the effects of an intravenous infusion of ovalbumin were tested in the anesthetized artificially ventilated guinea pigs. The renewed application of the antigen induced an initial increase of left ventricular pressure which was followed by a rapid decrease 5 min after antigenic challenge. Enddiastolic left ventricular pressure increased within 3 min, thus indicating left ventricular pump failure. In the same time range, ECG recordings uniformly showed signs of acute myocardial ischemia. In addition, heart rate steadily decreased. All animals died within 15 min. Simultaneously with cardiac anaphylactic malfunction, severe arterial hypoxia and carbon dioxide retention occurred, revealing respiratory distress.Histamine is known as a potent bronchoconstrictor via histamine H₁-receptor stimulation. Administration of H₁-recpetor antagonists to improve respiration may therefore provide further information on the contribution of pulmonary malfunction to anaphylactic cardiovascular shock. Therefore, additional experiments were performed with sensitized guinea pigs pretreated with the histamine H₁-receptor blocker mepyramine. In these experiments the antigenic challenge induced a dissociation of cardiac and respiratory manifestation of anphylaxis. Despite inhibition of hypoxia and carbon dioxide retention, left ventricular pump failure and occurrence of myocardial ischemia were delayed but not suppressed.It is concluded that histamine is an important mediator of anaphylactic respiratory distress. However, vasoactive anaphylactic mediators other than histamine are primarily involved in anaphylactic cardiac malfunction occurring during the later phase of systemic anaphylaxis.Supported by grant Fe 250/1-1 from the Deutsche Forschungsgemeinschaft (DFG).