Evidence for histamine H1 and H2 receptors in guinea-pig oxyntic cells

We have previously shown that histamine in the dose range of 1.0 X 10(-16) to 1.0 X 10(-14) M caused a linear increase in oxyntic cell carbonic anhydrase (CA) activity. A maximal dose of the H2 antagonist, cimetidine, reduced the action of histamine by only 74 +/- 7.8% suggesting a possible H1 component of histamine action on oxyntic cells. Using quantitative cytochemistry of CA activity in guinea-pig oxyntic cells, we compared the dose-response relationships (1.0 X 10(-17)-1.0 X 10(-9) M) of specific H2 (dimaprit, 4-methylhistamine, impromidine) and H1 (2-pyridylethylamine) agonists with histamine (H1 and H2). In addition, we studied the effects of the specific H2 antagonist, cimetidine, and H1 antagonist, mepyramine, on histamine, dimaprit and 2-pyridylethylamine-stimulated CA activity. We found that guinea-pig oxyntic cells respond to both H1 and H2 agonists. H1 agonists were more potent but less efficacious than H2 agonists. H2 agonists were more efficacious, but less potent than H1 agonists. Cimetidine (10(-10)-10(-8) M) was a competitive antagonist of dimaprit-stimulated CA activity. However, at higher doses (10(-5) M), cimetidine antagonism of histamine-stimulated CA activity was of a mixed noncompetitive and competitive type. Cimetidine and mepyramine exhibited both H2 and H1 antagonism, but their affinities for their respective agonists were greater. The data suggests that the oxyntic cell has receptors for both H1 and H2 agonists. H1 agonism is important at low concentrations of agonists. The H1 and H2 receptor components appear to be functionally linked.