Wilson C, Broadley KJ. Further characterization of the guinea pig left atrial tension response to histamine by use of selective agonists.
AGENTS AND ACTIONS 1981;
11:215-22. [PMID:
7257948 DOI:
10.1007/bf01967617]
[Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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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