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  • Title: Further characterization of the guinea pig left atrial tension response to histamine by use of selective agonists.
    Author: Wilson C, Broadley KJ.
    Journal: Agents Actions; 1981 May; 11(3):215-22. PubMed ID: 7257948.
    Abstract:
    1. The responses of guinea pig left atrial tension and right atrial rate to histamine receptor agonists and histamine were compared. 2. Single doses of histamine and another non-selective agonist, N,N-dimethylhistamine, produced biophasic inotropic responses, with an initial increase in tension and a secondary sustained tension increase separated by a negative inotropic component. 3. Selective H1-receptor agonists -- 2-methylhistamine, 3-methylhistamine and 2-pyridylethylamine (2-PEA) -- also exhibited biphasic inotropic responses. 2-PEA did so only after blockade with propranolol or in atria from reserpine-pretreated animals, indicating an additional release of endogenous catecholamines which masked the biophasic response. 4. Selective H2-receptor agonists -- 4-methylhistamine and dimaprit -- failed to produce biphasic responses except at high concentrations only in the case of 4-methylhistamine. 5. The biophasic responses were converted to monophasic responses by mepyramine. This was a result of antagonism of the initial positive component and the secondary negative component which were therefore mediated via H1-receptors. The production of a biphasic inotropic response therefore depends upon these two components which were exhibited preferentially by the H1-receptor-selective agonists.
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