Absorption of histamine from the gastrointestinal tract of dogs in vivo.

1. In anaesthetized dogs, various amounts of [(14)C]histamine were introduced into the lumen of a ligated intestinal loop or of the ligated stomach and the absorption of this histamine was studied by determining the radioactive histamine in the venous blood coming from the ligated part.2. After the introduction of 5-5000 mug [(14)C]histamine, into a loop of jejunum, or of 50 mug into a loop of duodenum, ileum or colon, radioactive histamine was detected in all eight successive 15 min samples of venous blood collected during 2 hr. The percentage recovery of the [(14)C]histamine in the blood during this period varied between 0.04 and 3.7.3. After the introduction of 10 mg [(14)C]histamine into the stomach, radioactive histamine was detected in all samples of gastric venous blood collected at various times during the following 4 hr.4. After the introduction of 50-5000 mug [(14)C]histamine into a loop of jejunum, radioactive histamine was also detected in the general arterial blood.5. When a jejunal loop was perfused through its artery with a dextransaline solution, the absorption of [(14)C]histamine from the lumen into the venous effluent was much greater than when the blood supply was kept intact.6. A large part of the [(14)C]histamine introduced into an intestinal loop was inactivated or destroyed either in the lumen or the wall since only a part was recovered in the venous blood, contents and wall of the loop at the end of 2 hr. When different amounts of [(14)C]histamine were introduced into a jejunal loop the recovery was shown to be dependent on the dose. With 5 mug it amounted to about 1% whereas with 5000 mug to 29-42%. The recovery of the [(14)C]histamine introduced into a perfused jejunal loop was greater.7. In dogs and cats large amounts of free histamine were found in the contents of the stomach 2 hr after a meat meal, and much smaller amounts in the contents of loops from the small intestine. The amounts found in the contents of loops from the colon varied greatly.8. In eighteen commercial dog and cat foods the free histamine contents were found to vary over fiftyfold, from 0.06 to 3.5 mg/100 g.9. The significance of the results is discussed in relation to the role of histamine as a humoral agent in the ;gastric' and ;intestinal phases' of gastric secretion.