Kinetics of antagonism at histamine-H1 receptors in isolated rabbit arteries.

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Onaran HO, Bokesoy TA

Kinetics of antagonism at histamine-H1 receptors in isolated rabbit arteries.

Naunyn Schmiedebergs Arch Pharmacol. 1990 Apr;341(4):316-23.

PubMed ID

1970615 [ View in PubMed

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Abstract

Kinetics of antagonist-induced decrease of histamine-H1 receptor-mediated steady-state responses in isolated rabbit arteries were studied in the presence of histamine-H2 receptor antagonist famotidine. Data were fitted using a model which describes competition kinetics at the receptor level. Estimated rate and equilibrium constants were evaluated for their dependence on tissue, agonist and antagonist concentrations, using (+)-brompheniramine as antagonist. In large arteries (thoracic and arcus aorta), rate constants were observed to be modified by agonist and/or antagonist concentrations, suggesting a diffusion-controlled process. In relatively small (common carotid and iliac) arteries, estimated equilibrium constants (and consequently the rate constants) were found to diverge despite the invariance of equilibration times between arteries, leading us to include the effects of spare receptors in our evaluation. A model describing the effects of receptor reserve on the estimated equilibrium dissociation constant was developed and stimulated and the results then compared with those that had been experimentally estimated. The reserve hypothesis was experimentally verified in common iliac artery (where EC50 much less than KA) using the irreversible antagonist phenoxybenzamine. A rationalized rule for the optimization of experimental design for in-vitro disequilibrium-competition experiments was proposed. Common carotic artery was found to be favorable for the present design in view of its reserve properties. In addition, competition reaction seems to be the rate-determining step in this artery. Rate and equilibrium constants of mepyramine, (+)-brompheniramine, diphenhydramine and antazoline were therefore determined in the common carotid artery and were compared with those obtained from independent experiments. Results suggest that the estimated parameters reflect drug-receptor interaction.

DrugBank Data that Cites this Article

Drug Targets

Drug	Target	Kind	Organism	Pharmacological Action	Actions
Brompheniramine	Histamine H1 receptor	Protein	Humans	Yes	Antagonist	Details
Dexbrompheniramine	Histamine H1 receptor	Protein	Humans	Yes	Antagonist	Details