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PubMedDate not supplied

Interaction of imidazoline alpha-adrenergic receptor antagonists with histamine receptors.

Because the alpha-adrenergic receptor antagonists phentolamine and tolazoline are similar in structure to histamine, it is possible that the vasodilatation caused by these drugs may be due in part to stimulation of histamine receptors. The vascular effects of these agents were studied in the hindquarters of rats and the gracilis muscle of dogs. To eliminate interruption of sympathetic vasoconstrictor tone as a mechanism of vasodilatation, all animals were treated with the alpha-adrenergic receptor antagonist, dibozane. After dibozane, histamine caused vasodilatation in the rat, whereas both tolazoline and phentolamine caused vasoconstriction. It is concluded that phentolamine and tolazoline do not stimulate vascular histamine receptors in the rat. In the dog, after alpha-receptor blockade, phentolamine and tolazoline caused vasodilatation, as did histamine. Responses to histamine were partially attenuated by mepyramine and greatly attenuated by the combination of mepyramine and metiamide, indicating the participation of both H1- and H2-histamine receptors. Vasodilatation caused by phentolamine was not reduced by antihistamines and does not appear to involve histamine receptors. Vasodilatation following tolazoline was blocked by metiamide but not mepyramine. It is concluded that in addition to blockade of alpha-adrenergic receptors, tolazoline can cause vasodilatation by stimulation of histamine H2-receptors.

Adrenergic alpha-Antagonists↗
PubMed1977

Histamine-receptor leucocytes (HRL). Organ and lymphoid subpopulation distribution in man.

The frequency of lymphoid cells with a membrane receptor for histamine was determined in various lymphoid organs in man using a histamine-rosette assay. Thymus had very low numbers of histamine-receptor cells while lymph node and peripheral blood had increasing percentages. Through a combination of cell separation techniques, we demonstrated that about one third (1/3) of peripheral blood B lymphocytes and macrophages carry histamine receptors. Immature B cells or null cells (E-rosette and membrane-immunoglobulin-negative) do not have this receptor. Only 10% of peripheral blood T lymphocytes formed histamine rosettes. That these histamine receptor T lymphocytes are a subpopulation representing the differentiated suppressor/cytotoxic T cells is suggested by evidence showing complete removal of histamine receptor T lymphocytes on nylon wool adherence columns. Thus, the histamine receptor is expressed on differentiated B and T lymphocytes and may serve as a marker for developed suppressor/cytotoxic T cells in man.

B-Lymphocytes↗
PubMed1977

Selective display of histamine receptors on lymphocytes.

Histamine, acting on histamine type 2 receptors, increases intracellular cyclic adenosine monophosphate (AMP) and thus modulates the immunologic functions of lymphocytes. Lymphocyte cyclic AMP levels were used to follow the development of histamine receptors. The B lymphocytes have no functional histamine receptors. As T lymphocytes "mature" in immunologic function--from thymocytes to cortisone-resistant thymocytes to splenic T lymphocytes--their response to histamine increases. The response of these subpopulations of lymphocytes to isoproterenol is the inverse of the histamine response. It is suggested that the changing display of histamine receptors plays an important part in the control of immunologic responses.

Animals↗
PubMed1977

Purification of histamine receptor (VI). An improved double labeling method with "double protection".

Studies were done on the specific labeling of the histaminergic H1-receptor of the longitudinal smooth muscle of cat small intestine. A procedure involving 'double protection' combined with the double labeling technique was developed. The first protection was the usual with a protective antihistamine, promethazine, and the second was cross protection of non-specific sites with non-hitaminergic drugs, thioriazine and atropine. Muscle tissue protected with promethazine against non-radioactive dibenamine was treated with 3H-dibenamine in the presence of these second protectors. The second protectors covered non-receptor sites which had been protected from non-radioactive dibenamine with promethazine. The dose-response curves were carefully checked in each experiment to confirm that the second protectors did not interfere with the specific coverage provided by the first protector. Finally 14C-dibenamine was applied to measure non-specific binding after which the labeled muscles were fractionated and the radioactivity was counted. The specificity of labeling achieved in the receptor-rich fraction by this method is discussed.

Animals↗
PubMed1977

Purification of histamine receptor. (IV) Specificity of binding of various drugs to the histamine receptor-rich fraction and to solubilized binding sites.

Studies were made on tritiated histamine binding to the receptor-rich membrane fraction and solubilized sites and its displacement by various drugs. H1-Agonists and antagonists displaced histamine most effectively. A H2-agonist and atropine were less effective and propranolol, phentolamine and imidazole acetic acid had little effect. The solubilized binding sites showed the same specificity of binding as the membrane fraction. Membrane fragments had two binding constants, whereas solubilized sites had only one. Solubilized sites bound similar amounts of histamine and dibenamine: the latter was applied to intact tissue under conditions which would presumably cause specific binding to histamine receptors. These binding characteristics show that the method used was adequate for purification of histamine receptors from smooth muscle of cat small intestine.

Animals↗
PubMed1976

Depression of rat cerebral cortical neurones by H1 and H2 histamine receptor agonists.

Histamine (H) and H1 agonists 2-pyridylethylamine (PEA) and 2-methylhistamine (2-MH) produced a greater depression of the corticospinal and unidentified rat cerebral cortical neurones than did 4-methylhistamine (4-MH), an H2 agonist. Mepyramine antagonized the effects of 2-MH, PEA and H, and partially antagonized the depression induced by 4-MH. Metiamide and cimetidine, H2 antagonists, blocked 4-MH and H but not 2-MH- and PEA-induced depression. These results indicate that H-induced depression of cortical neurones involves activation of H1 and H2 receptors.

Acetylcholine↗
PubMed1979

Effects of histamine receptor antagonists on histamine-induced responses in human skin.

The effects of intradermally administered histamine H1- and H2-receptor antagonists on the cutaneous responses--redness, weal, flare and itch--induced by intradermal injection of histamine were studied in man. Weal and redness were studied after blockade of the axon reflex by local infiltration with lidocaine. All responses were significantly inhibited by the H1-receptor antagonist mepyramine. The H2-antagonists cimetidine and metiamide reduced flare and itch significantly but not to the same extenet as mepyramine and not in a clearly dose-related manner. The size of weal and redness was not significantly reduced by cimetidine. No further reduction of flare, itch or weal was obtained by adding metiamide or cimetidine to mepyramine. After blockade of the axon reflex with lidocaine the histamine-induced weals turned white at the centre. This blanching was more prominent when histamine was injected in combination with cimetidine. Substituting mepyramine for cimetidine resulted in small weals with an intense red colour. It is concluded that, apart from being engaged in the direct vasodilatory response to histamine, H2-receptors do not seem to be involved in the other cutaneous responses to histamine studied.

Adult↗
PubMed1977

Stimulatory (H1) and inhibitory (H2) histamine receptors in gallbladder muscle.

The nature of histamine receptors in gallbladder muscle and examined using specific histamine-receptor agonists and antagonists. The H2-receptor antagonist, metiamide, augmented the contractile response to histamine indicating that gallbladder muscle possessed stimulatory H1 receptors and inhibitory H2 receptors. The independent inhibitory character of H2 receptors was confirmed by (1) induction of relaxation with histamine after H1-receptor blockade and the suppression of this relaxation with metiamide, and (2) induction of relaxation with a specific H2-receptor agonist, 4-methyl histamine and the suppression of this relaxation with metiamide. Further, blockade of H2 but not of H1 receptors augmented the response to the octapeptide of cholecystokinin. The nature of this effect was such that the apparent affinity of the octapeptide for its own receptor was increased. The finding raised the possibility that in their native unoccupied state, H2 receptors may modify the response to hormonal agents.

Animals↗
PubMed1975

Classification and biological distribution of histamine receptor sub-types.

The distribution and classification of histamine receptors in mammalian and avian tissues have been summarized in Tables 1-4. It is evident that histamine receptors are present on a number of morphologically distinct cell types and the proportion of cells bearing H1- and H2-receptors varies not only with the species but also with the cell source. The pharmacological receptors mediating mepyramine-sensitive histamine responses have been defined as H1-receptors. Receptors mediating mepyramine-resistant, but burimamide or metiamide-sensitive histamine responses have been classified as H2-receptors. Histamine responses mediated via H2-receptors seem to involve the adenylcyclase system resulting in elevation of intracellular cyclic-AMP level, which is susceptible to burimamide blockade but insensitive to beta-adrenergic blocking agents. This mode of action of histamine involving H2-receptors and the adenyl cyclase system has been shown to stimulate the mammalian heart; promote gastric acid secretion; inhibit antigen-induced histamine release from leucocytes and inhibit lymphocyte-mediated cytotoxicity. It can further be concluded that both H1- and H2-receptors are widely distributed throughout the animal body in the gastro-intestinal, reproductive, respiratory and cardiovascular systems, nervous system and on mast cells and blood leucocytes. In these tissues, histamine receptors play an important role in physiological, immunological and immunopathological processes. Interaction of histamine with both H1- and H2-receptors in varying proportions modulates the overall manifestation of cardiovascular and respiratory syndromes during certain immunopathological conditions (e.g. inflammation, allergy and anaphylaxis). Histamine receptors also appear to play and important role in the development of immuno-competence and immunity.

Adrenal Medulla↗
PubMed1978

Occurrence of H2-inhibitory histamine receptors in chicken ileum.

Metiamide (H2-histamine receptor antagonist) blocked histamine-induced relaxations and significantly potentiated contractile responses to histamine on isolated spiral strips of chicken ileum. This investigation showed the presence of H2-inhibitory receptors in chicken ileum.

Animals↗