HOMEOSTASIS IN THE SYMPATHECTOMIZED DOG

Abstract

Cold usually caused a primary rise in body temp. of normal dogs succeeded by a fall below the basal level. Sympathectomized dogs showed no initial rise and a somewhat greater drop in body temp. The maximal decreases in temp. did not differ significantly in the 2 groups. In cold environments shivering began sooner and continued at a faster rate in dogs lacking the sympathetic chains; there were no noteworthy differences in the rise of body temp. or the rate of panting which followed exposure to high temp. Sympathectomized dogs endured an O tension of 6% for 5 hrs. as well as normal controls with no obvious symptoms except an increased rate of respiration; exposure to 4% O2 was somewhat less well withstood, but there were no differences in the recovery after anoxemia. Sympathectomized dogs given insulin showed a greater decrease in blood-sugar and a more frequent occurrence and a greater severity of hypoglycemic symptoms; fasting blood-sugar levels were the same as in normal dogs. The remarkable ability of sympathectomized dogs, as compared with sympathectomized cats, to endure unfavorable environmental conditions is attributed to numerous accessory physiological devices, not under sympathetic control: larger lungs and heart per kg. of body wt., greater blood vol., higher Hb content, abundant salivary flow and a long tongue for heat loss, and a common resort to shivering for heat production. In insulin hypoglycemia these devices were unavailing; then the effects were similar in the 2 animals.