Effects of Histamine Receptor Antagonists on Ion Transport by Isolated Ileum of the Rabbit

Abstract

In contrast to gastric mucosa, little is known about the effects of histamine on small intestinal mucosa. This study examines some of the effects of histamine and its antagonists on ion transport by isolated ileal mucosa. Histamine causes a transient increase in short-circuit current which is blocked by H 1 , but not by H 2 receptor antagonists. H 1 receptor antagonists cause a marked decrease in short-circuit current which is not associated with a significant change in net Na and Cl transport. Since H 1 receptor antagonists reduce the residual ion flux to a negligible value, the effects of histamine antagonists on alkali secretion were measured. Isolated ileal mucosa of the rabbit has two components of alkali secretion. The major component requires HCO 3 on the serosal side of the mucosa, whereas the minor component originates from the mucosa itself. H 1 receptor antagonists inhibit both components of alkali secretion. The effects of H 2 receptor antagonists appear to be qualitatively similar to H 1 receptor antagonists, but the effects of H 2 receptor antagonists are transient. Assuming specificity of histamine receptor antagonists in the concentrations used, the data suggest that tissue stores of histamine in the ileum may play a fundamental role in regulating alkali secretion, which is inhibited by antihistamines of the H 1 type.