Stimulation of cell proliferation by histamine H2 receptors in dimethylhdrazine-induced adenocarcinomata

Cell proliferation in dimethylhydrazine-induced colonic carcinomata was stimulated by histamine and by the histamine H2 receptor agonist dimaprit and inhibited by the histamine H2 receptor antagonists Metiamide and Cimetidine but not by the histamine H1 receptor antagonist Mepyramine. In contrast histamine had no effect on colonic crypt cell proliferation in normal or dimethylhydrazine-treated rats.     

Modification by histamine H2-receptor blockade of acid secretion stimulated by histamine, pentagastrin and methacholine in the isolated whole mouse stomach.

The direct influences of the blockade of the gastric histamine H2-receptors on the secretory actions induced by histamine, pentagastrin and methacholine, have been studied on the isolated perfused whole mouse stomach. According to the results cimetidine did not modify the spontaneous basal acid secretion. The interactions of cimetidine with the secretagogues were of a competitive nature with histamine and non-competitive with pentagastrin, while no modification of methacholine stimulated acid secretion.     

Demonstration of histamine H2 receptors on human melanoma cells

Histamine induced a concentration-dependent increase in intracellular cyclic-AMP of the two human melanoma cell lines SK23 and DX3.LT5.1; maximal stimulation was obtained with 17.8 microM histamine which consistently produced greater than 50-fold increases in the cyclic AMP content of both cell lines. The dose-response curve for histamine in each culture was progressively displaced to the right with increasing concentrations of the histamine H2 receptor antagonist cimetidine. Ranitidine, another H2 receptor antagonist also prevented the histamine-induced cyclic AMP elevation, but the H1 receptor antagonists mepyramine and tripelennamine had no significant effect. These findings indicate that human melanoma cells express histamine H2 receptors, stimulation of which activates adenylate cyclase with a subsequent rise in intracellular cyclic AMP. Mast cell:melanoma interactions mediated by histamine in vivo might therefore be expected to modify some aspects of melanoma cell behaviour.     

Occurrence of atypical histamine H2 receptors in the wall of the frog subclavian vein

Selective H2-histamine agonist dimaprit was shown to produce relaxation of the isolated frog subclavian vein, with it persisting under the effect of selective H2-histamine antagonist cimetidine. Possible nonspecific mechanisms of relaxation produced by histamine are discussed. The data presented do not exclude that there are atypical H2-histamine receptors in subclavian vein of frogs, the activation of which initiates the attenuation of the active tension.     

CLIC4 interacts with histamine H3 receptor and enhances the receptor cell surface expression

Histamine H3 receptor (H3R), one of G protein-coupled receptors (GPCRs), has been known to regulate neurotransmitter release negatively in central and peripheral nervous systems. Recently, a variety of intracellular proteins have been identified to interact with carboxy (C)-termini of GPCRs, and control their intracellular trafficking and signal transduction efficiencies. Screening for such proteins that interact with the C-terminus of H3R resulted in identification of one of the chloride intracellular channel (CLIC) proteins, CLIC4. The association of CLIC4 with H3R was confirmed in in vitro pull-down assays, coimmunoprecipitation from rat brain lysate, and immunofluorescence microscopy of rat cerebellar neurons. The data from flowcytometric analysis, radioligand receptor binding assay, and cell-based ELISA indicated that CLIC4 enhanced cell surface expression of wild-type H3R, but not a mutant form of the receptor that failed to interact with CLIC4. These results indicate that, by binding to the C-terminus of H3R, CLIC4 plays a critical role in regulation of the receptor cell surface expression.     

Characterization of thromboxane A2/prostaglandin H2 receptors and histamine H1 receptors in cultured guinea-pig tracheal smooth-muscle cells.

We characterized thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptors and histamine H1 receptors in Guinea-pig cultured tracheal smooth-muscle cells (TSMC). [3H]SQ 29,548 (a TXA2 antagonist)-binding sites were saturable and a high affinity with a dissociation constant of 6.2 +/- 0.60 nM (mean +/- S.E.) and a receptor density of 46 +/- 4.6 fmol/10(6) cells. [3H]SQ 29548 binding was completely inhibited by TXA2 mimetics or antagonists. Intracellular calcium concentration ([Ca2+]i) in TSMC was increased with U46619 stimulation and the increase was attenuated by TXA2 antagonists, the potencies of which correlated with those inhibiting the activities of the [3H]SQ 29548 binding. [3H]Mepyramine (a H1 antagonist)-binding sites were also present in TSMC. [3H]Mepyramine had a single class of low-affinity-binding sites with a dissociation constant of 2.6 +/- 0.081 microM and a receptor density of 10.6 +/- 0.11 nmol/mg protein. [3H]Mepyramine binding in TSMC membrane was inhibited by H1 antagonists, but not by H2 antagonists. The inhibition constants of mepyramine in TSMC were 910-times lower than those in tracheal membranes. In contrast, the histamine-induced increase in [Ca2+]i in TSMC was inhibited in the presence of low concentrations of H1 antagonists. All these observations provide evidence that TXA2/PGH2 receptors, mepyramine-binding sites and/or H1 receptors are expressed in cultured TSMC.     

Necessity of intracellular cyclic AMP in inducing gastric acid secretion via muscarinic M3 and cholecystokinin2 receptors on parietal cells in isolated mouse stomach

The existence of a direct action of acetylcholine and gastrin on muscarinic M3 and cholecystokinin2 (CCK2) receptors on gastric parietal cells has not yet been convincingly established because these stimulated acid secretions are remarkably inhibited by histamine H2 receptor antagonists. In the present study, we investigated the necessity of intracellular cyclic AMP in inducing gastric acid secretion via muscarinic M3 and CCK2 receptors on parietal cells using an isolated mouse stomach preparation. Bethanechol (10-300 microM) produced a marked increase in acid output and this increase was completely blocked by famotidine (10 microM). In the presence of famotidine, bethanechol (1-30 microM) augmented the acid secretory response to dibutyryl AMP (200 microM) in a concentration-dependent manner. The augmentation was blocked by atropine (1 microM), 4-DAMP (0.1 microM), a muscarinic M3-selective antagonist, and by Ca2+ exclusion from the serosal nutrient solution. Pentagastrin (0.3-3 microM) also concentration-dependently stimulated gastric acid secretion, but the effect was completely inhibited by famotidine. In the presence of famotidine, pentagastrin (0.1-0.3 microM) elicited a definite potentiation of the acid secretory response to dibutyryl cyclic AMP (200 microM). This potentiation was inhibited by YM022 (1 microM), a CCK2 receptor antagonist, and by exclusion of Ca2+ from the serosal nutrient solution. The present results suggest that gastric acid secretion via the activation of muscarinic M3 and CCK2 receptors on the parietal cells is induced by activation of the cyclic AMP-dependent secretory pathway.     

Regulation of parietal cell migration by gastrin in the mouse

Recent studies suggest that gastrin regulates parietal cell maturation. We asked whether it also regulates parietal cell life span and migration along the gland. Dividing cells were labeled with 5'-bromo-2'-deoxyuridine (BrdU), and parietal cells were identified by staining with Dolichos biflorus lectin. Cells positive for D. biflorus lectin and BrdU were reliably identified 10-30 days after BrdU injection in mice in which the gastrin gene had been deleted by homologous recombination (Gas-KO) and wild-type (C57BL/6) mice. The time course of labeling was similar in the two groups. The distribution of BrdU-labeled parietal cells in wild-type mice was consistent with migration to the base of the gland, but in Gas-KO mice, a higher proportion of BrdU-labeled cells was found more superficially 20 and 30 days after BrdU injection. Conversely, in transgenic mice overexpressing gastrin, BrdU-labeled parietal cells accounted for a higher proportion of the labeled pool in the base of the gland 10 days after BrdU injection. Gastrin, therefore, stimulates movement of parietal cells along the gland axis but does not influence their life span.     

H2 histaminic receptors in rat cerebral cortex. 2. Inhibition of [3H]histamine by H2 antagonists

Sites labeled by [3H]histamine in homogenates of rat cerebral cortex reveal a pharmacological specificity typical of H2 receptors. Fourteen H2 antagonists inhibit the specific binding of the radioligand to the same level; Hill coefficients are near or equal to one for five compounds and markedly lower for nine. The binding patterns of individual antagonists (A) are well described by the empirical expression Y = F1K1/(K1 + [A]) + F2K2/(K2 + [A]), in which F1 and F2 sum to 1; F2 is 0 for those drugs that reveal a Hill coefficient of 1. Concentrations of A that reduce specific binding by 50% (IC50) correlate well (r = 0.991; P less than 0.00001) and show good numerical agreement with potencies reported for inhibition of the response to histamine in H2-mediated systems. The correlation is poorer when IC50 is replaced by either K1 (r = 0.973) or K2 (r = 0.921) for those antagonists that reveal both; the antihistaminic activity of the drug thus appears not to be associated preferentially with one or other class of sites. Since F2 varies from 0.16 to 0.60 among those antagonists that discern heterogeneity, the antagonist appears to determine the distribution of sites between the two classes. Moreover, a correlation among antagonists between values of K1 and K2 (r = 0.975; P = 0.00001) suggests that the apparent heterogeneity reflects different conformers within an otherwise homogeneous population. H2 antagonists appear to be noncompetitive with respect to each other and to the radioligand: one antagonist has relatively little effect on the values of K1, K2, and F2 revealed by another; also, estimates of K1 and K2 are independent of the concentration of [3H]histamine between 1.3 and 10 nM, although the radioligand exhibits an apparent dissociation constant of 3.9 nM [Steinberg, G. H., Eppel, J. G., Kandel, M., Kandel, S. I., & Wells, J. W. (1985) Biochemistry (preceding paper in this issue)].     

Differential activation of dual signaling responses by human H1 and H2 histamine receptors

Stimulation of human H1 and H2-histamine receptors (HRs) primarily activates signaling pathways to increase intracellular calcium [Ca2+]i and cyclic AMP (cAMP), respectively. Activation of H2-HR in human embryonic kidney (HEK) cells by histamine and dimaprit increases both cAMP formation and [Ca2+]i, as determined by cAMP-scintillation proximity assays and fluorescence imaging plate reader (FLIPR) assays. In HEK cells expressing relatively high levels of H2-HR (Bmax=26 pmol/mg protein), histamine and dimaprit are full agonists in eliciting cAMP responses with pEC50 values of 9.30 and 7.72 that are 1000-fold more potent than their respective pEC50 values of 6.13 and 4.91 for increasing [Ca2+]i. The agonist potencies decrease for both responses at lower H2-HR density (5 pmol/mg protein) and dimaprit exhibits partial agonist behavior for the [Ca2+]i response. The inverse agonists ranitidine and cimetidine more potently inhibit cAMP production in the higher expressing H2-HR line. Histamine also activated both signaling pathways via human H1-HRs highly expressed (Bmax=17 pmol/mg protein) in HEK cells, with a 1000-fold greater potency for [Ca2+]i vs. cAMP responses (pEC50=7.86 and 4.82, respectively). These studies demonstrate a markedly different potency for activation of multiple signaling pathways by H1- and H2-HRs that may contribute to the selectivity of histamine responses in vivo.     

Implication of prostaglandins and histamine H1 and H2 receptors in radiation-induced temperature responses of rats

Exposure of rats to 1-15 Gy gamma radiation (60Co) induced hyperthermia, whereas 20-200 Gy induced hypothermia. Exposure either to the head or to the whole body to 10 Gy induced hyperthermia, while body-only exposure produced hypothermia. This observation indicates that radiation-induced fever is a result of a direct effect on the brain. The hyperthermia due to 10 Gy was significantly attenuated by the pre- or post-treatment with a cyclooxygenase inhibitor, indomethacin. Hyperthermia was also altered by the central administration of a mu-receptor antagonist naloxone but only at low doses of radiation. These findings suggest that radiation-induced hyperthermia may be mediated through the synthesis and release of prostaglandins in the brain and to a lesser extent to the release of endogenous opioid peptides. The release of histamine acting on H1 and H2 receptors may be involved in radiation-induced hypothermia, since both the H1 receptor antagonist, mepyramine, and H2 receptor antagonist, cimetidine, antagonized the hypothermia. The results of these studies suggest that the release of neurohumoral substances induced by exposure to ionizing radiation is dose dependent and has different consequences on physiological processes such as the regulation of body temperature. Furthermore, the antagonism of radiation-induced hyperthermia by indomethacin may have potential therapeutic implications in the treatment of fever resulting from accidental irradiations.     

Effect of histamine and H1 and H2 receptors antagonists on carbachol-induced wet-dog shakes in rats

Intracerebroventricular administration of carbachol chloride induced a characteristic wet-dog shake response in rats. Histamine did not change the number of wet-dog shakes during a 60 min observation but intensified the number of episodes in the first 30 min of the experiment. Antagonists of H1 (thenalidine and antazoline) and H2 (cimetidine and ranitidine) receptors, attenuated carbachol-induced wet-dog shakes. It may be suggested that inhibition of the central histaminergic structures decreased central cholinergic activity.     

Brain histamine and histamine H3 receptors following repeated L-histidine administration in rats

In order to assess the importance of the chronic increase in precursor availability on central histaminergic mechanisms in rats, nine male Wistar rats received L-histidine orally at a dose of 1000 mg/kg, twice daily (07.00 h and 19.00 h) for 1 week; 9 rats were used as controls. Brain tissue histamine and tele-methylhistamine levels, as well as plasma histamine concentration were assayed. Binding properties and regional distribution of the autoregulatory histamine H3 receptors in brain were studied with [3H]-R-alpha-methylhistamine receptor binding and autoradiography. In L-histidine loaded rats, tissue histamine levels in cortex, hypothalamus, and rest of the brain were significantly increased by 40%-70%. Histamine concentrations in cerebellum and plasma, and tele-methylhistamine concentrations in cortex and hypothalamus did not change. The binding properties of H3 receptors in cortex were not altered. However, there were changes in the regional distribution of [3H]-R-alpha-methylhistamine binding sites, suggestive of a region-selective up-/down-regulation of histamine H3 receptors or their receptor sub-types. These results imply that following repeated L-histidine administration in the rat (1) there is enhanced synthesis of brain histamine not reflected in its functional release; (2) the excess of histamine is sequestered and stored rather than being metabolized; (3) histamine H(3) receptor binding properties are not altered, whereas receptor density is changed in selected regions. In conclusion, these results demonstrate that the neuronal mechanisms controlling histamine synthesis, storage, and release are adaptable and allow the sequestration of the excess of histamine in order to prevent excessively high neuronal activity.     

Retinol enhances differentiation of the gastric parietal cell lineage in developing rabbits.

In the gastric glands, parietal cells are the targets for anti-ulcer drugs because they contain the proton pump or HK-ATPase responsible for acid secretion. Little is known about factors influencing developmental expression and activity of HK-ATPase. In this study, the parietal cell lineage was investigated in rabbits at post-natal days 0 (P0) to P60 by using morphological and biochemical methods. Immunohistochemical and ultrastructural studies show that the HK-ATPase-expressing cells that appear at P0 and P3 are pre-parietal cells. However, terminally differentiated, mature parietal cells make their appearance at P7. These data correlate with the activity of HK-ATPase, measured as K(+)-dependent hydrolysis of p-nitrophenyl phosphate. Three-day-retinol treatment of P3-P30 rabbits induced an increase in the (i) production of parietal cells, (ii) intensity of the HK-ATPase immunostaining per cell, (iii) activity of HK-ATPase and (iv) amount of HK-ATPase protein measured by Western blotting. In conclusion, retinol upregulates the development of HK-ATPase in rabbits, perhaps due to precocious acceleration of the differentiation program of parietal cell lineage.     

Alterations in cyclic AMP metabolism associated with photoreceptor cell degeneration in the C3H mouse

Previous studies have shown an abnormality in cyclic nucleotide phosphodiesterase activity in the retina of mice (C3H/HeJ) with an inherited degeneration of the photoreceptor layer. Adenyl cyclase activity and cyclic AMP content have been measured in C3H retina and compared with that in normal retina (DBA/1J) during postnatal maturation, to assess the influence of the mutation upon cyclic AMP metabolism. Adenyl cyclase activity increases normally for the first 7 days of age; thereafter, it becomes greater than normal. Cyclic AMP becomes obviously abnormal after 10 days of age. The elevated levels of cyclic AMP persist in the surviving cells of the inner layers of the adult C3H retina. Adenyl cyclase activity and cyclic AMP content are concentrated in the inner layers of the normal retina, while the photoreceptor layer has only a very low level of enzyme activity and cyclic AMP. The data suggest that the synthesis of cyclic AMP in the inner layers of C3H retina is significantly enhanced, during the period of postnatal development in which the photoreceptor cells have begun to degenerate.     

Characterization of functional histamine H1 receptors on a cultured smooth muscle cell line

Cultured cells of the smooth muscle line DDT1MF-2, which was derived from a hamster vas deferens tumor, expressed histamine H1-type receptors and responded biochemically and functionally to H1-specific stimulation. The H1-receptor antagonist [3H]-pyrilamine bound specifically to 9.7 x 10(6) sites/DDT1MF-2 cell with a dissociation constant (Kd) of 219 nM. The addition of histamine to suspensions of fura-2-loaded DDT1MF-2 cells elicited a rapid, transient, and stimulus concentration-dependent increase in the intracellular concentration of Ca2+ with an EC50 of 3 x 10(-5) M, which demonstrated H1 receptor specificity. Moreover, in order to evaluate in vitro contractile response of individual DDT1MF-2 cells, the degree of intracellular actin polymerization was quantified by a DNase inhibition assay. The percentage of nonpolymerized or G-actin in DDT1MF-2 cells was reduced in a histamine concentration-dependent manner with an EC50 of 1 x 10(-5) M and H1 receptor specificity. Histamine-induced actin polymerization was accompanied by changes in cell shape that were consistent with cellular contraction, as assessed by flow cytometry. The H1-type receptors of cultured DDT1MF-2 cells thus couple histamine stimulation to a variety of functional responses of smooth muscle cells.     

H2 histaminic receptors in rat cerebral cortex. 3. Inhibition of [3H]histamine by H2 agonists

The binding of [3H]histamine to H2 receptors in homogenates of rat cerebral cortex is inhibited by 11 H2 agonists in a characteristic and unique manner. At low concentrations of the radioligand (less than 1.5 nM), the inhibitory profiles of individual agonists (A) are distinctly biphasic; specific binding is well described in most cases by the empirical expression Y = F1K1/(K1 + [A]) + F2K2/(K2 + [A]), in which F1 and F2 sum to 1. Maximal inhibition is the same for all agonists. Since values of F2 vary from 0.42 to 0.90, the agonist appears to determine the equilibrium distribution of receptors between two states of affinity. Ratios of apparent affinity (K2/K1) vary from 204 to 3 090 000, and there is no correlation between values of K1 and K2. Compounds lacking H2 activity, including structural analogues of histamine and dimaprit, reveal a Hill coefficient of 1 and inhibit the radioligand only weakly. For six agonists, values of K2 agree and correlate well (P = 0.00047) with H2 pharmacological potency (EC50) in the guinea pig right atrium; for the others, K2 is less than EC50 by 15-61-fold. Four observations suggest that the inhibition corresponding to F1 is allosteric and cooperative: the dissociation constant of the radioligand appears to vary in the presence of an unlabeled agonist, absolute levels of binding corresponding to F1, as defined by dimaprit, decrease at higher concentrations of [3H]histamine, F1 for dimaprit is reduced from 0.48 to 0.32 by 2-methylhistamine (F1 = 0.27) at a concentration of 20 nM (approximately K1(0.5) K2(0.5) for 2-methylhistamine), but the increase in K1 for dimprit is at least 100-fold less than expected from competitive effects, and 1 equiv of some agonists appears to preclude access of [3H]histamine to more than 1 equiv of receptors, with no evidence that an appreciable fraction of the unlabeled drug is bound. Noncompetitive effects also may account in part for the inhibition corresponding to F2.     

Involvement of histamine H1 and H2 receptors in hypothermia induced by ionizing radiation in guinea pigs

Radiation-induced hypothermia was examined in guinea pigs. Exposure to the head alone or whole-body irradiation induced hypothermia, whereas exposure of the body alone produced a small insignificant response. Systemic injection of disodium cromoglycate (a mast cell stabilizer) and cimetidine (H2-receptor antagonist) had no effect on radiation-induced hypothermia, whereas systemic and central administration of mepyramine (H1-receptor antagonist) or central administration of disodium cromoglycate or cimetidine attenuated it, indicating the involvement of central histamine through both H1 and H2 receptors in this response. Serotonin is not involved, since the serotonin antagonist methysergide had no effect on radiation-induced hypothermia. These results indicate that central histaminergic systems may be involved in radiation-induced hypothermia.