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  • Title: The determination of receptor constants for histamine H2-agonists in the guinea-pig isolated right atrium using an irreversible H2-antagonist.
    Author: Rising TJ, Steward A.
    Journal: Br J Pharmacol; 1986 Jan; 87(1):211-6. PubMed ID: 2869811.
    Abstract:
    From measurements of chronotropy in the guinea-pig isolated right atrium, a compound (E1309) was found which behaved as an irreversible antagonist at the histamine H2 receptor. E1309 was used to block irreversibly a proportion of the H2 receptors and the dissociation constants, relative efficacies and receptor reserves of four H2-agonists were determined. The calculated dissociation constants were similar to the Ki values reported from H2-radioligand binding studies but different from the observed EC50 values. The order of potency for the four H2-agonists was impromidine much greater than histamine greater than dimaprit greater than 4-methylhistamine. The order of relative efficacy was 4-methylhistamine greater than dimaprit greater than histamine greater than impromidine, the natural agonist not being the most efficacious. This atypical finding is discussed in relation to other receptor classes.
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