STUDIES ON TEMPERATURE DISTRIBUTION AND HEAT PRODUCTION IN THE "CORE AREA" OF THE DOG

Abstract

Temperature distribution within the "oore area" of fasting mongrel dogs was studied with thermocouples or "applicators" (the hot junctions of thermocouples - manufactured by ELLAB Ltd. Copenhagen). The highest intra-abdominal temperature was found in the lumen of the duodenum, followed in turn by temperatures within the lumen of the ileum, large intestine and the stomach, as well as temperatures in the liver, hepatic and portal veins. With the exception of the rectum, temperatures within the gastro intestinal tract, the liver and its associated vessels were found at least 0.3°C higher than that of aortic blood. The effect of mild hemorrhage and environmental cooling on the pattern of distribution as well as the values of the organ-aorta temperature differentials within the "core area was studied. This caused a rise in the organ-aorta temperature differentials of various regions of the g.i.t. with the exception of the rectum in which it caused a fall. It had no noticeable effect on the values of those of the liver, portal and hepatic veins. Environmental cooling caused a rise in the values of the organ-aorta temperature differentials of all regions of the gastro-intestinal tract, the liver, portal and hepatic veins. The blockade of adrenergic influences with bretylium tosylate in the warm environment caused noticeable but transient falls in the values of the organ-aorta temperature differentials of most regions of the gastro intestinal tract (except the rectum in which a rise was obtained), and a slight fall in those of the liver and its associated vessels. The response of these regions of the gastro-intestinal tract, and the liver to environmental cooling were slightly reduced after bretylium tosylate. The effects of the blockade of cholinergic mechanism with atropine sulphate and vagotomy were also studied. Atropine sulphate caused a distinct fall in the temperature differentials between the various regions of the gastro-intestinal tract and the aorta. It also caused a fall in that of a liver, but no change in those of the hepatic and portal veins. These reactions were also transient. The response of the stomach to environmental cooling was enhanced while those of the other regions of the g.i.t were reduced by atropine sulphate. The response of the liver, hepatic and portal veins to environmental cooling were also reduced. Cervical vagotomy in the warm environment caused a rise in the temperature differentials of almost all regions of the gastro-intestinal tract, and hepatic vein. It caused no significant alteration in the temperature differentials of the liver and portal vein. The response of the stomach and rectum to environmental cooling after abdominal vagotomy were enhanced while that of the large intestine was reduced. The response of the ileum was abolished and that of the duodenum was reversed. Simultaneous administration of atropine sulphate and bretylium tosylate in the warm environment caused a fall in the temperature differentials of the upper regions of the gastro intestinal tract but a rise in that of the rectum. The response of the stomach, ileum and large intestine and were reduced while that of the duodenum was abolished by these drugs. The response of the rectum was enhanced. Gut sterilization with neomycin sulphate did not cause a material alteration in the values of the temperature differentials of the various regions of the gut, as well as those of the liver and its associated vessels. The response of the rectum and large intestine to environmental cooling after gut sterilization were slightly reduced while those of the other regions of the gut as well as those of the liver and its associated vessels, were either unaltered or enhanced. The importance of these findings in the maintenance and regulation of the temperature of the "core area” is discussed.