Objective: The objective was to investigate the role of histamine in the porcine caecum with special regard to its release and permeation.
Material and methods: Caecal epithelia were mounted in Ussing chambers. Mast cells were stimulated by A23187 (1 micromol/l). Permeation and changes in short-circuit current (Isc) were assessed after unilateral application of 3H-labelled histamine (100 micromol/l). Mucosal-to-serosal (ms) and serosal- to-mucosal (sm) flux rates were calculated based on the contralateral appearance of radioactive histamine label (hist-rad; representing histamine plus catabolites) as well as histamine. 14C-mannitol fluxes were measured to assess paracellular permeability.
Results: Both A23187 and serosal addition of histamine increased Isc of caecal epithelia. The Isc increase due to A23187 was associated with an elevated histamine release from epithelia. A discrepancy between hist-rad and histamine fluxes (P<0.05) indicated efficient histamine catabolism (ca. 85%), which was decreased by blockage of diamine oxidase through aminoguanidine. Fluxes of histamine were correlated to 14C-mannitol fluxes. Fluxes of hist-rad and histamine were higher in the sm direction.
Conclusions: Histamine can be released from endogenous stores and acts on the epithelium. The absorption of luminal histamine is predominantly restricted by paracellular permeability and catabolism. The latter is only partially catalysed by diamine oxidase.