A Delimitation of the Central Nervous Mechanism Involved in Reflex Hyperglycemia.

Abstract

Claude Bernard's sugar puncture experiments furnished some evidence of the existence of a bulbar control of carbohydrate mobilization, but efforts to locate a specific center responsible for the piqÛre diabetes have been rather inconclusive. Furthermore, temporary hyperglycemia and glycosuria often follow any injury to the brain. On the other hand, numerous investigators have shown that specific centers within the diencephalon may play some part in the regulation of carbohydrate metabolism. Cannon and Rapport 1 produced additional evidence of a localized central control of the blood sugar level by locating a center in the medulla which is responsible for the reflex activity of the adrenal glands. Griffith 2 studied the various factors involved in a reflex hyperglycemia and found that the liver and the adrenal glands are chiefly responsible for the rise. Bard 3 suggested that a comparison of the reflex rises in blood sugar, obtained from intact animals and from animals after various parts of the central nervous system had been removed, might furnish additional information concerning the location of the centers controlling carbohydrate mobilization.

Before an attempt could be made to detect abnormalities in the reflex hyperglycemic reactions, control experiments had to be performed in which the central nervous system had been left intact. Twenty-six such experiments were performed: 10 of the animals were anesthetized by chloralose (0.1 gm. per kilo) administered by mouth; 10 by intravenously injected sodium barbital (0.28 gm. per kilo) and 6 by intraperitoneally injected sodium barbital (0.3 gm. per kilo). Comparable results were obtained in all cases and therefore sodium barbital, injected intravenously, was generally employed in subsequent experiments. Three blood samples were taken at half-hour intervals before stimulation; after a 3-minute period of interrupted (10 sec. on, 5 sec. off, 10 sec. on, —) tetanic stimulation of the right brachial nerve, blood samples were taken at intervals of one minute, 10 minutes, 30 minutes, one hour, and sometimes 2 hours.