Heat production in the gastro-intestinal tract of the dog.

1. Mean temperature from the lumen of the dog duodenum was 0.6 degrees C hotter than aorta. Ileum, stomach and large intestine were slightly cooler but still about 0.5 degrees C hotter than aorta.2. Portal vein averaged 0.35 degrees C hotter than the aorta.3. From portal blood flow data and aortic-portal temperature differentials heat production was calculated for the 10 kg dog as 3.4 kcal/hr. Evidence is adduced to show in these experiments that the gastro-intestinal tract produced 60% more heat than the liver. Total splanchnic heat production was about 33% of the total bodily heat production.4. The following procedures were carried out: adrenergic neurone blockade, atropine administration, vagotomy, prior starvation, bowel sterilization. All were without effect. It was concluded that smooth muscle activity, active transport or microbiological activity were unlikely to be sufficient to account for the high level of heat production.5. It was suggested that mucosal activity was the most likely source of heat. The possible involvement of unidentified metabolic pathways was discussed but oxidative mechanisms alone were shown not to be sufficient explanation.6. Since the rectal temperature was not significantly different from aortic it was concluded that the rectum was metabolically inactive and usually passively assumed the temperature of its blood supply.