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In vivo characterization of histamine H 1 ‐ and H 2 ‐receptors in the rat stomach microcirculation
Author(s) -
Koo A.
Publication year - 1983
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.1476-5381.1983.tb09379.x
Subject(s) - mepyramine , cimetidine , in vivo , agonist , histamine , schild regression , thioperamide , histamine h2 receptor , antagonist , receptor , histamine h1 receptor , microcirculation , histamine receptor , chemistry , vasodilation , receptor antagonist , pharmacology , medicine , endocrinology , biology , biochemistry , microbiology and biotechnology
1 Using a video microscope system, an in vivo microcirculation preparation was designed to characterize histamine receptors in the rat stomach submucosal arterioles (diameter 50 μm). 2 Each in vivo stomach microcirculation preparation received topically applied multiple concentrations of either the selective histamine H 1 ‐ or H 2 ‐ receptor agonist and antagonist and the respective responses (changes of the arteriolar diameter) were used to construct the concentration‐response curves. 3 Results showed that both 2‐thiazolylethylamine and impromidine, the respective selective H 1 ‐and H 2 ‐receptor agonists, produced concentration‐dependent vasodilator responses in the in vivo stomach submucosal arterioles. These vasodilator responses were competitively and selectively blocked by the respective H 1 ‐receptor antagonist mepyramine and the H 2 ‐receptor antagonist cimetidine. 4 Data from each in vivo preparation were examined separately to yield a Schild plot and a Hill plot, from which the in vivo estimates of the pA 2 value, the slope of the Schild plot, and the Hill coefficient were obtained. 5 The estimated pA 2 values for mepyramine (9.60 ± 0.033, mean ± s.e. mean) and cimetidine (5.98 ± 0.037) conformed to similar values found in other tissues, showing that the rat stomach microvascular H 1 ‐ and H 2 ‐receptors are of the same nature as similar receptors elsewhere. 6 Both the Hill and the Schild plots yielded regressions with unity slopes, indicating that the agonist‐receptor and the antagonist‐receptor reactions followed a simple one‐to‐one stoichiometry. 7 The findings in the present study are discussed and compared with those from other in vitro tissue preparations; it appears that the present in vivo technique is a satisfactory system for characterizing receptors in the vascular smooth muscle of the microcirculation.