Abstract
A slow, but significant, histamine inactivation was found in the tissues of the fore-stomachs. The inactivation was significantly higher in rumen muscle than in rumen epithelium (11.2 and 6.4 µg histamine diphosphate/g wet weight/hr., respectively). In abomasal epithelium no significant inactivation was detected. At optimal substrate concentrations homogenates of duodenal, jejunal and ileal mucosa inactivated 32.0, 85.8 and 103.1 µg/g wet weight of tissue/hr., respectively. Preformed histamine in the intestinal mucosa on the other hand, decreased from duodenum to ileum. In ileal and jejunal mucosa the inactivation in homogenates was significantly larger than in epithelium left as intact as possible. Most of the histamine inactivation by the epithelium in the digestive tract was counteracted by aminoguanidine, indicating that oxidative deamination is the major pathway for histamine inactivation in these tissues in vitro.