Is the airway epithelium responsible for histamine metabolism in the trachea of guinea pigs?

The aim of the study was to investigate whether or not the epithelium plays an active role in histamine metabolism, via the histaminase and/or methyltransferase pathways. Isolated tracheas from guinea pigs sensitized to egg albumin (EA) were used. The epithelium was either left intact or removed from the preparations. The tracheal tubes were mounted in a chamber, allowing estimation of smooth muscle tension, and perfused with buffer. In some experiments the perfusate was collected for determination of histamine and methylhistamine. Mepyramine was used to evaluate the contribution of histamine to the EA-induced contraction. Mepyramine reduced the contraction by 90% when the epithelium was removed; with intact epithelium the reduction was 47%. Aminoguanidine, a histaminase inhibitor, significantly potentiated the response to EA when the epithelium was left intact. Traces of methylhistamine were detected in tissue extracts and perfusates. We conclude that histaminase is present in the preparation and that it can contribute to the inhibitory effect of the epithelium by means of histamine degradation.