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PubMed1987

Histamine and lactate dehydrogenase (LDH) release in ischemic myocardium of the guinea-pig.

Histamine has been proved to be released during myocardial infarction and ischemic arrhythmias in dogs. The aim of the present experiments was to evaluate if ischemia and reperfusion modify histamine and lactate dehydrogenase (LDH) release in isolated guinea-pig heart. The results obtained show a steady increase of LDH release both in the ischemic and reperfusion phases. The release of histamine was reduced during the ischemic phase and increased significantly during reperfusion. A significant diminution of mast cell granule metachromasia was observed in the right auricles at the end of the reperfusion period. D-mannitol and reduced glutathione (GSH) modified the kinetics of histamine and LDH release. Cimetidine was able to decrease significantly the release of histamine during the ischemic and reperfusion phases and also reduced the release of LDH; triprolidine was completely ineffective. The results suggest that oxygen-derived free radicals may be involved in the pathogenesis of myocardial dysfunction after ischemia and reperfusion.

Animals↗
PubMed1996

Acute paw oedema formation induced by ATP: re-evaluation of the mechanisms involved.

ATP-induced inflammation was investigated using subplantar injection in the mouse hind paw. The order of efficacy of purinoceptor agonists for inducing paw oedema (30 nmol per paw) was ATP = alpha, beta-methylene ATP = 2-methylthio ATP > adenosine > UTP > ADP > AMP. Diadenosine polyphosphates effectively induced paw oedema formation with an order of efficacy of: P1,P4-di(adenosine-5')tetraphosphate = P1,P5-di(adenosine-5')-pentaphosphate = P1,P6-di(adenosine-5')hexaphosphate >>ATP = P1,P3-di(adenosine-5')triphosphate > P1,P2-di(adenosine-5')pyrophosphate. Systemic administration of P2-purinoceptor antagonists (30-100 mu mol/kg), suramin, 4,4'-diisothiocyanatostilbene-2,2'-disulphonate, pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid and cibacron blue, reduced the intensity of ATP-induced oedema. At 30 mu mol/kg 8-(p-sulfophenyl)theophylline (non-selective adenosine receptor antagonist), 3,7-dimethyl-1,1-propargylxanthine (adenosine A2 receptor antagonist), triprolidine (histamine H1 receptor antagonist), ranitidine (histamine H2 receptor antagonist) and ketanserin (5-hydroxytryptamine 5-HT2 receptor antagonist), but neither 8-cyclopentyl-1,3-dipropylxanthine (adenosine A1 receptor antagonist), nor indomethacin (cyclooxygenase inhibitor) inhibited the ATP-induced swelling. Topical (100 nmol per paw), but not systemic (100 mu mol/kg) administration of NG-nitro-L-arginine methyl ester (nitric oxide synthase inhibitor) reduced the intensity of the ATP-induced paw oedema. These results show that ATP can induce an inflammatory oedematous reaction and contribute to our understanding of the underlying mechanisms.

Adenosine Triphosphate↗
PubMed2001

Increased histidine decarboxylase expression during in vitro monocyte maturation; a possible role of endogenously synthesised histamine in monocyte/macrophage differentiation.

OBJECTIVE: In this study the expression of histidine decarboxylase (HDC), the pivotal enzyme in histamine formation and the effect of endogenously produced histamine on differentiation antigens was examined during in vitro differentiation of human monocytes. MATERIAL AND TREATMENT: Human elutriated monocytes from healthy volunteers were incubated with macrophage colony stimulating factor (M-CSF) and the expression of HDC was followed at both mRNA and protein levels. To study the possible function of histamine we followed the expression of some cell surface markers (CD14, CD16, CD91, CD49d and CD11c) relevant for phagocytic differentiation upon incubation in the presence of different histamine inhibitors, an HDC inhibitor: S(+)-alpha-fluoromethyl-histidine HCl, (alphaFMH), a compound that disturbs the interaction of histamine with intracellular cyp450 moieties: N,N-diethyl-2-[4-(phenylmethyl) phenoxy]-ethanamine HCI, (DPPE); and H1 and H2 receptor antagonists, Triprolidine and Cimetidine. RESULTS: During in vitro culture of elutriated human monocytes, in the presence of M-CSF, the gene expression and biosynthesis of HDC was considerably increased. The various antihistamine agents decreased the expression of the cell surface markers examined in this study. CONCLUSIONS: These data support the elevation of HDC expression during human monocytic differentiation and the possibility that monocyte-derived histamine is partially involved in regulation of M-CSF induced in vitro human monocyte/macrophage phagocytic differentiation.

Antigens, CD↗
PubMed1998

ATP release caused by bradykinin, substance P and histamine from intact and cultured smooth muscles of guinea-pig vas deferens.

Histamine (60 microM) produced ATP release from segments of guinea-pig vas deferens which was blocked by pyrilamine and triprolidine, H1-blockers, but not by ranitidine, an H2-blocker. The evoked-release was inhibited by the mitochondrial inhibitors, carbonyl cyanide-m-chlorophenylhydrazone (CCCP) and oligomycin. Bradykinin (BK) and substance P (SP) also caused substantial and moderate release of ATP, respectively. The BK-evoked release of ATP was inhibited by HOE140, a B2-antagonist, but not by [Des-Arg10] HOE140, a B1-antagonist. On the other hand, VIP, angiotensin II (AII) and cholecystokinin-octapeptide (CCK-8) failed to elicit a measurable release of ATP. Histamine and BK also enhanced the release of ATP from superfused cultured smooth muscle cells. These results suggest that ATP may be released as an autacoid from the smooth muscles in the presence of these chemical mediators.

Adenosine Triphosphate↗
PubMed2004

Activation of histamine H1-receptor enhances neurotrophic factor secretion from cultured astrocytes.

OBJECTIVE: Histamine stimulates nerve growth factor (NGF) secretion from cultured astrocytes. Histamine H(1)-receptor antagonists completely block its effect. In the present study, we determined the involvement of histamine-receptor subtypes in this process. MATERIALS AND METHODS: Radioligand-binding assay was used to establish the presence of histamine H(1)- and H(2)-receptors on new-born rat cortical astrocytes in primary culture. Histamine H(1)-, H(2)- and H(3)/H(4)-receptor ligands, and highly selective protein kinase C (PKC) inhibitor were used to influence NGF secretion from cultured astrocytes. NGF, released into the culture medium, was measured by NGF-ELISA. RESULTS: Histamine H(1)-receptor agonists (histamine, selected histaprodifens) increased the secretion of NGF from cultured astrocytes in a concentration-dependent manner. H(1)-receptor antagonists/inverse agonists (mepyramine, triprolidine) and PKC inhibitor completely blocked the effect of histamine. Histamine H(2)- and H(3)-receptor agonists did not enhance NGF secretion significantly. In addition, H(2)- and H(3)/H(4)-receptor antagonists did not diminish histamine-stimulated NGF release. CONCLUSIONS: Our results indicate that histamine H(1)-receptor and PKC are involved in the signal transduction pathway, responsible for histamine-stimulated NGF secretion from cultured astrocytes.

Animals↗
PubMed2003

Molecular characterization of specific H1-receptor agonists histaprodifen and its Nalpha-substituted analogues on bovine aortic H1-receptors.

We determined the molecular properties of the selective and potent H(1)-receptor agonist histaprodifen and its N(alpha) substituted analogues: methyl-, dimethyl-, and imidazolylethyl-histaprodifen (suprahistaprodifen). All derivatives show high affinity for (3)H-mepyramine labeled bovine aortic H(1)-receptor binding sites with the following order of potency: suprahistaprodifen > dimethylhistaprodifen > methylhistaprodifen > histaprodifen > histamine. Suprahistaprodifen and dimethylhistaprodifen were the most potent displacers of (3)H-mepyramine binding (K(i)=4.3 and 4.9 nM, respectively). Histaprodifen, methylhistaprodifen and suprahistaprodifen binding was differentially influenced by GTP, whereas dimethylhistaprodifen was not affected. All drugs, except dimethylhistaprodifen, were activators of G-proteins. Their order of potency was suprahistaprodifen > histamine > histaprodifen > methylhistaprodifen. Their effect on G-protein activation was abolished by the addition of the H(1)-receptor antagonist triprolidine (10 microM), which given alone did not activate G-proteins. Our data suggest that histaprodifens are potent but heterogeneous H(1)-receptor ligands with diverse effects on the molecular level in our model system. While the histaprodifen, methylhistaprodifen and suprahistaprodifen data are in agreement with their agonistic nature, as shown in the functional studies performed on different species (rat and guinea pig H(1)-receptor), dimethylhistaprodifen behaved as an antagonist in our study.

Animals↗
PubMed1987

Serotonergic, adrenergic and histaminergic receptors coupled to phospholipase C in cultured cerebellar granule cells of rats.

Phosphatidylinositol (Ptdlns) turnover has been studied in the primary culture of granule cells dissociated from the cerebellum of postnatal rat. Addition of serotonin (5-hydroxytryptamine, 5-HT) caused an increase (300-600% of control) of [3H]inositol monophosphate (IP1) accumulation in the presence of LiCl in cells prelabeled with [3H]myo-inositol. The EC50 and saturation concentrations of 5-HT were about 0.1 and 10 microM respectively. Some nonselective 5-HT receptor agonists, MK212, 5-methoxytryptamine, tryptamine and quipazine, were capable of stimulating IP1 accumulation; a selective 5-HT1A receptor agonist, 8-OH-DPAT, was ineffective. The 5-HT-induced response was potently blocked by several 5-HT2 receptor antagonists such as ketanserin, mianserin, spiroperidol and pyzotyline. The 5-HT-induced accumulation was dependent on the culturing time of granule cells with the maximal response seen in an 8-day culture. Norepinephrine (NE) also promoted an increased IP1 accumulation (300% of the control) with an EC50 of about 1 microM, while prazosin inhibited this NE-induced response with a Ki of about 0.2 nM. The responses induced by NE and 5-HT appeared to be additive. In addition, histamine in a dose-dependent manner enhanced the accumulation by about 100%; this histamine effect was blocked by triprolidine, an H1 receptor antagonist, but not by cimetidine, an H2 receptor antagonist. These results suggest that 5-HT, NE and histamine could be part of the neurotransmitter substances present in mossy fibers or other afferent nerve endings which innervate granule cells in vivo and that Ptdlns turnover regulated by their selective receptors on granule cells may play a role in modulating the excitatory function of these neurons.

Animals↗
PubMed1991

Decreased histamine H1 receptors in the frontal cortex of brains from patients with chronic schizophrenia.

Involvement of histamine H1 receptor in the brains of schizophrenic patients was investigated using 3H-mepyramine as a ligand. The specific 3H-mepyramine binding in the frontal cortex was saturable with the dissociation constant (Kd) of about 0.6 nM and the maximum number of binding sites (Bmax) of 64 fmol/mg protein. Specific H1 antagonists, mepyramine (Ki = 1.4 nM), promethazine (Ki = 1.4 nM), diphenylpyraline (Ki = 4.1 nM), triprolidine (Ki = 5.3 nM), diphenylhydramine (Ki = 35 nM), but not the specific H2 antagonist, cimetidine (Ki greater than 10(5) nM), strongly inhibited the 3H-mepyramine binding. Regional distribution of the specific 3H-mepyramine binding was in the order of: frontal cortex greater than hippocampus greater than cerebellum greater than hypothalamus greater than thalamus, putamen, and pallidum. The specific 3H-mepyramine binding in schizophrenic brains was reduced by 56% in the frontal cortex. Representative Scatchard analyses of the specific 3H-mepyramine binding revealed changes resulting from a decrease in receptor density but not in receptor affinity. Down-regulation of the histamine H1 receptor in the frontal cortex may be involved in the pathophysiology of schizophrenia.

Adult↗
PubMed1981

Two distinct serotonin receptors: regional variations in receptor binding in mammalian brain.

Two distinct serotonin receptors in mammalian brain are labeled respectively with [3H]serotonin (5-HT1) and [3H]spiperone (5-HT2). In general agonists display highest affinities for 5-HT1 while antagonists prefer 5-HT2 sites. To conduct regional studies of 5-HT receptors, we estimated 5-HT2 sites with [3H]spiperone, using the 5-HT2 specific antagonist cinanserin to displace binding to 5-HT2 but not dopamine receptors and sulpiride to displace [3H]spiperone from dopamine but not 5-HT receptors. About 15% of cerebral cortical [3H]spiperone binding appears to involve dopamine sites and the remainder involves 5-HT2 receptors. In the corpus striatum about 80% of [3H]spiperone binding labels dopamine receptors and the rest involves 5-HT2 sites. [3H]mianserin binds about equally to 5-HT2 and histamine H1-receptors. [3H]mianserin interactions with 5-HT2 sites are studied selectively by displacing histamine H1-receptor binding with the H1-antihistamine triprolidine. [3H]LSD labels both 5-HT1 and 5-HT2 receptors. Its binding to 5-HT1 sites is displaced selectively with 5-HT, while its binding to 5-HT2 receptors is displaced with cinanserin. [3H]5-HT labels only 5-HT1 receptors. The regional distribution of the two 5-HT receptors is similar in rat, guinea pig and bovine brain. However, the regional patterns of 5-HT1 and 5-HT2 receptors differ considerably in all 3 species. The hippocampus is quite high in 5-HT1 receptors but low in 5-HT2 sites. The cerebellum contains the lowest levels of both 5-HT1 and 5-HT2 receptors. In bovine brain, most areas contain similar numbers of 5-HT1 and 5-HT2 receptors. However, the substantia nigra, the richest 5-HT1 area in bovine brain, possesses 10 times more 5-HT1 than 5-HT2 sites.

Animals↗
PubMed1985

Actions of betahistine at histamine receptors in the brain.

The actions of betahistine (N alpha-methyl-2-pyridylethylamine) on brain histamine receptors were investigated in a series of biological models. [3H]Mepyramine binding to H1-receptors in membranes from guinea-pig cerebellum was inhibited by betahistine with a Ki value of 31 microM. The binding of [3H]mepyramine in brain of the living mouse was inhibited by betahistine in high dosages (150-300 mg/kg). In slices from mouse cerebral cortex, betahistine induced [3H]glycogen hydrolysis in a concentration-dependent manner with an EC50 value of 9.0 microM with a maximal effect 57% that of histamine. Mepyramine and triprolidine, two H1-receptor antagonists, inhibited the betahistine-induced glycogenolysis with Ki values of 28 nM and 7 nM respectively. In slices from guinea-pig hippocampus, betahistine stimulated the accumulation of cyclic AMP in the presence of 5 microM impromidine, a H2-receptor agonist. The maximal effect represented 22% of that elicited by histamine at the H1-receptor and the EC50 value was 32.4 microM. Mepyramine at 0.1 microM partially blocked the response to betahistine. Together these various observations indicate that betahistine is a partial agonist at cerebral H1-receptors. Finally, betahistine was not an agonist at histamine H3-autoreceptors but was a rather potent antagonist of the inhibitory effect of exogenous histamine on [3H]histamine release elicited by K+ depolarisation in slices from rat cerebral cortex (Ki = 6.9 microM).

Animals↗
PubMed1986

Phosphoinositide hydrolysis mediated by histamine H1-receptors in rat brain cortex.

Histamine stimulated the accumulation of [3H]inositol 1-phosphate in the presence of lithium in [3H]inositol-prelabelled slices from rat brain cortex in a concentration-dependent manner, with an EC50 value of 94.7 microM. High concentrations of antagonists of histamine H2 receptors, muscarinic receptors, alpha 1-adrenoceptors and serotonin receptors did not inhibit the effect. The histamine H1-receptor antagonists mepyramine, triprolidine, promethazine, d-chlorpheniramine and the tricyclic antidepressant doxepin inhibited the response with Ki values corresponding to an interaction with histamine H1-receptors. The EC50 for the response was about three times lower than the Ki value (approximately 300 microM) for the inhibition by histamine of [3H]mepyramine binding to membranes from rat brain cortex. Partial inactivation of H1-receptors with the alkylating antagonist phenoxybenzamine resulted in similar reductions in [3H]mepyramine binding sites and in the maximal histamine-induced [3H]inositol 1-phosphate accumulation, without affecting the KD for the radioligand or the EC50 for the response. The apparent dissociation constant for histamine calculated from these experiments (KA = 92.2 microM) was not different from the EC50 value. The present results indicate that histamine-stimulated phosphoinositide hydrolysis in rat brain cortex is mediated by H1-receptors and that no receptor reserve is present.

Animals↗
PubMed1993

N alpha-methylhistamine inhibits intestinal transit in mice by central histamine H1 receptor activation.

The effects of (R)alpha-methylhistamine and N alpha-methylhistamine on intestinal transit were examined in mice. The passage of a charcoal meal in the gastrointestinal tract was dose dependently inhibited by N alpha-methylhistamine (1-20 mg/kg i.p.), but not by a selective H3 receptor agonist (R)alpha-methyl-histamine (1-50 mg/kg i.p.). The inhibitory effect of N alpha-methylhistamine (20 mg/kg) was attenuated by pretreatment with H1 receptor antagonists (mepyramine 5 mg/kg i.p. or 5 micrograms i.c.v. and triprolidine 5 mg/kg i.p.), but not by cimetidine (10 mg/kg i.p.), zolantidine (5 mg/kg i.p.), a brain-penetrating H2 receptor antagonist, or thioperamide (5 mg/kg i.p.), a selective H3 receptor antagonist. The effect of N alpha-methylhistamine was also attenuated by combined treatment with phentolamine and propranolol (5 and 15 mg/kg s.c., respectively) and by pretreatment with 6-hydroxydopamine (20 mg/kg i.p., 2 days before). N alpha-Methylhistamine markedly decreased histamine turnover in the mouse brain. These findings suggest that intestinal transit is inhibited by N alpha-methylhistamine via stimulation of central H1 but not H3 receptors and that stimulation of the sympathetic system is involved in this effect.

Animals↗
PubMed1985

The use of derivative and least-squares methods to analyse a polypharmaceutical product by UV spectrophotometry.

Derivative UV spectrophotometry is well established for analysing pharmaceutical products containing more than one drug. By contrast, the least-squares method for over-determined systems is rarely used, because it is assumed that measurements at a large number of wavelengths are needed to obtain good results. Both methods have advantages, and their use in combination is useful for analysing polypharmaceuticals. A combination of derivative and least-squares methods was used to analyse tablets containing pseudoephedrine hydrochloride, triprolidine hydrochloride and dextromethorphan hydrobromide. Pseudoephedrine was determined by derivative spectrophotometry. The other drugs were determined by the least-squares method at higher wavelengths where pseudoephedrine does not absorb. Satisfactory precision for the least-squares method was obtained with a manual spectrometer measuring at six wavelengths and calculating the results with a microcomputer.

Journal Article↗
PubMed1986

High pass digital filtering applied to quantitative UV spectrometry.

High pass digital filtering is a novel method of data treatment for quantitative UV spectrometry in the presence of broad interfering bands. The test and standard spectra are digitally filtered using the binomial filter to remove low frequency components and a least squares fit of the standard to the test is then carried out. This paper reports a preliminary evaluation of the method, including a theoretical comparison with derivative spectrometry and the successful application to a typical problem in pharmaceutical analysis, the assay of the decongestant pseudoephedrine hydrochloride in the presence of the antihistamine triprolidine hydrochloride. The procedure should also be suitable for enhancing the specificity of other spectroscopic techniques.

Journal Article↗
PubMed2005

Analysis of pharmaceutical preparations containing antihistamine drugs by micellar liquid chromatography.

Rapid chromatographic procedures for analytical quality control of pharmaceutical preparations containing antihistamine drugs, alone or together with other kind of compounds are proposed. The method uses C18 stationary phases and micellar mobile phases of cetyltrimethylammonium bromide (CTAB) with either 1-propanol or 1-butanol as organic modifier. The proposed procedures allow the determination of the antihistamines: brompheniramine, chlorcyclizine, chlorpheniramine, diphenhydramine, doxylamine, flunarizine, hydroxyzine, promethazine, terfenadine, tripelennamine and triprolidine, in addition to caffeine, dextromethorphan, guaifenesin, paracetamol and pyridoxine in different pharmaceutical presentations (tablets, capsules, suppositories, syrups and ointments). The methods require minimum handling sample and are rapid (between 3 and 12 min at 1 mLmin(-1) flow rate) and reproducible (R.S.D. values<5%). Limits of detection are lower than 1 microgmL(-1) and the recoveries of the analytes in the pharmaceutical preparations are in the range 100+/-10%.

1-Butanol↗
PubMed2000

A novel phenylaminotetralin (PAT) recognizes histamine H1 receptors and stimulates dopamine synthesis in vivo in rat brain.

A series of novel phenylaminotetralins (PATs) previously was shown to recognize discrete binding sites that are stereoselectively labeled by [3H]-(-)-trans-1-phenyl-3-N,N-dimethylamino-1,2,3,4-tetrahydronaphthalen e (H2-PAT) and highly localized in catecholaminergic nerve terminal regions in guinea pig forebrain. Furthermore, certain PATs stimulate tyrosine hydroxylase and dopamine synthesis in guinea pig and rat brain in vitro. In the current studies, we characterized sites labeled by [3H]-(-)-trans-H2-PAT and measured effects of PATs on dopamine synthesis in vivo in rat brain. [3H]-(-)-Trans-H2-PAT binds saturably (Bmax approximately 13 fmol/mg protein) and with high affinity (K(D) approximately 0.5 nM) to a single population of sites in rat brain. The ligand binding profile of [3H]-(-)-trans-H2-PAT labeled sites is very similar to histamine H1 receptors labeled with [3H]-mepyramine. After i.c.v. injection to rats, (+/-)-trans H2-PAT (4-40 nmoles/kg) stimulates dopamine synthesis (to about 180% of control levels) selectively in the limbic brain region nucleus accumbens vs. the extrapyramidal region striatum; this effect is fully blocked by (+/-)-cis-H2-PAT and the H1 antagonist triprolidine. At higher doses (> 40 nmoles/kg), the observed stimulation of dopamine synthesis is attenuated to control levels, likely due to activation of feedback mechanisms resulting from non-receptor mediated displacement of intraneuronal dopamine. We propose that PATs represent a novel class of ligands for H1 receptors that can modulate tyrosine hydroxylase activity and dopamine synthesis in the limbic region of mammalian forebrain.

Animals↗
PubMed1999

Histamine and histamine-receptor antagonists modify gene expression and biosynthesis of interferon gamma in peripheral human blood mononuclear cells and in CD19-depleted cell subsets.

The effect of histamine and histamine antagonists was examined on gene expression and biosynthesis of bacterial endotoxin (LPS) induced interferon gamma (IFNgamma) both in human peripheral mononuclear cells (PMBC) and in T-cell enriched fractions. We found, that histamine inhibited the LPS induced transcription of IFNgamma gene and biosynthesis of IFNgamma protein in PMBC and also in CD19-depleted cell populations. The inhibitory effect of histamine could be reversed by the H2 histamine receptor (HR2) antagonists cimetidine and ranitidine both in PMBC and in CD19-depleted cells, but not with triprolidine, an H1 receptor antagonist, suggesting that the inhibition of IFNgamma production is mediated through H2 receptors in these cell populations. In contrast to the inhibitory effect of histamine, cimetidine alone (in the absence of exogenous histamine) strongly stimulated both the IFNgamma mRNA and protein production, whereas this effect was hardly seen by and other H2 receptor blocker, ranitidine. This superinduction of IFNgamma gene by cimetidine disappeared if the CD19+ cells are removed from PMBC. These results suggest, that inhibition of IFNgamma gene expression by histamine is a direct effect of histamine on H2 receptor of T lymphocytes; however, the superinduction of IFNgamma by cimetidine requires the presence of other (probably primarily B) cell subsets.

Antigens, CD19↗
PubMed2000

Selective ligands as tools to study histamine receptors.

In this review the histaminergic ligands for the histamine H(1), H(2) and H(3) receptors, which are currently used as tools in pharmacological studies, are described. To study interactions with the histamine H(1) receptor, the H(1) agonist 2-aminoethylthiazole has long since been used. However, during the last decade, 2-phenylhistamine derivatives emerged with interesting binding features. So far no radiolabelled selective H(1) agonist has been commonly used. As H(1) antagonists mepyramine, triprolidine and chlorpheniramine are described together with radiolabelled H(1) antagonists [3H]mepyramine and [3H]doxepin. Special attention has been paid to the PET ligands [11C]doxepin and [11C]mepyramine and the [125I] labelled antagonists [125I]iodobolpyramine and [125I]iodoazidophenpyramine. Concerning H(2) agonists, especially dimaprit, amthamine and impromidine are discussed. There are several H(2) antagonists; amongst them cimetidine, tiotidine and ranitidine are used most frequently. Many of these antagonists behave as inverse agonists. As radiolabelled H(2) antagonists, [3H]cimetidine, [3H]tiotidine, [125I]iodoaminopotentidine and [125I]iodoazidopotentidine are included. Commonly used histamine H(3) agonists are N(alpha)-methylhistamine, (R)alpha-methylhistamine, imetit and immepip. Both methylhistamines are also available as [3H] labelled ligands. As reference compounds, often used H(3) antagonists are thioperamide, clobenpropit, iodophenpropit and impentamine. Most important radiolabelled H(3) antagonists are S-[3H]methylthioperamide, [3H]thioperamide, [125I]iodophenpropit and [125I]iodoproxyfan. The use of all these compounds as a tool in pharmacology is also discussed.

Animals↗