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Selectivity of 4‐methylhistamine at H 1 ‐ and H 2 ‐receptors in the guinea‐pig isolated ileum
Author(s) -
Barker L.A.,
Hough L.B.
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.tb11050.x
Subject(s) - receptor , mepyramine , agonist , dissociation constant , histamine , ileum , histamine receptor , chemistry , dimaprit , guinea pig , stereochemistry , medicine , endocrinology , biology , biochemistry , antagonist
1 The selectivity of 4‐methylhistamine (4‐MH) as an agonist at histamine H 1 ‐ and H 2 ‐receptors has been evaluated in the guinea‐pig isolated ileum. 2 The EC 50 values of 4‐MH on H 1 ‐ and H 2 ‐receptors that mediate contractile responses were determined. The EC 50 at H 1 ‐receptors was estimated after selective blockade of H 2 ‐receptors by tiotidine and the EC 50 at H 2 ‐receptors estimated after selective blockade of H 1 ‐receptors by mepyramine. 3 The ‐log EC 50 values at H 1 ‐ and at H 2 ‐receptors were 4.57 and 5.23, respectively. 4 The dissociation constants for the interaction of 4‐MH with H 1 ‐ and H 2 ‐receptors were determined. 5 The ‐log K D values at H 1 ‐ and H 2 ‐receptors were 3.55 and 4.27, respectively. 6 These results suggest that 4‐MH is only about 5 times as potent at H 2 ‐ as it is at H 1 ‐receptors in the guinea‐pig ileum and that 4‐MH should be used with caution to discriminate between H 1 ‐ and H 2 ‐receptors.