Effects of H2-blockers on rat mesenteric arterioles under resting conditions

H2-receptor but not H1-receptor antagonists, administered by intravenous infusion, produce a dose-dependent constriction of superior mesenteric arterioles of the anaesthetized rat under resting conditions. However the possibility that this effect could be related to a blockade of H2 receptors is unlikely, since their potency on blood flow changes does not parallel known H2-receptor antagonist activity. Furthermore, the estimated potency ratio is not in the expected order if the vasoconstriction is due to H2-antagonism, the potency ratios on guinea-pig atrial muscle and on mouse gastric acid secretion being famotidine greater than oxmetidine greater than ranitidine greater than cimetidine.