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Some effects of histamine in the depolarized rat uterus
Author(s) -
BLYTH D. I.
Publication year - 1973
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1973.tb17255.x
Subject(s) - histamine , calcium , chemistry , acetylcholine , egta , endocrinology , medicine , biophysics , biology , organic chemistry
Summary1 The relaxant effect of histamine in the isolated rat uterus remained after the preparation was depolarized in a potassium Ringer. 2 The effect was abolished by the calcium‐chelating agent, ethyleneglycol bis‐aminoethyl ether‐tetraacetic acid (EGTA). 3 Histamine caused relaxation during calcium‐induced contractures in a depolarized uterus treated with EGTA, but did not produce relaxation during barium‐induced contractures. 4 While responses of a normally polarized rat uterus to acetylcholine were inhibited by histamine, those of a depolarized uterus were enhanced by histamine. The inhibitory effects of isoprenaline and papaverine on acetylcholine responses were maintained in depolarized preparations. 5 Both the enhancing effect of histamine on responses to acetylcholine and the relaxation of calcium‐induced contractures were abolished by burimamide, indicating that H 2 ‐receptors mediate the effects of histamine in the depolarized tissue. 6 A reduction in the rate of exchange of calcium across the depolarized cell membrane was demonstrated with high concentrations of histamine. 7 The results are consistent with the hypothesis that in the rat uterus, the stimulation of H 2 ‐receptors by histamine is accompanied by a reduction in calcium exchange across the membrane which may result in a decrease in the concentration of free intracellular calcium available to stimulate contraction of the myofilaments. Histamine may act by increasing the binding of calcium within the cell.