Uptake and formation of histamine by the tissues of rabbits and cats

14C-histidine was administered orally to cats and rabbits and by intravenous infusion of rabbits. At various times up to 72 hr later, 14C-histidine was found in stomach, lung, liver and duodenum of both species. In rabbits, labelled histamine was also found in ear tip skin and blood cells. Similar results were obtained when labelled histidine was given orally to cats and rabbits in which the gastrointestinal tract had been previously sterilized by oral administration of an antibiotic mixture, showing that the labelled histamine was not formed in the intestinal tract by bacteria. 14C-histamine was also found in all these tissues of both rabbits and cats after its intravenous infusion, but none was found in any of the tissues tested after oral administration of labelled histamine, although it could be detected in venous blood for many hours, showing that some of the administered histamine was absorbed from the intestine. Since the tissue testes took up intravenously administered histamine, the amount absorbed after its oral administration must be too low for uptake to be detected.