The glucose, glycogen and aerobic glycolysis of isolated cerebral tissues

Abstract

The glucose of cere-bral tissues fell rapidly on excision, but was restored when the tissue respired in glucose saline; the level in the tissue remained below that of the saline. The glycogen of the tissue, also rapidly lost on excision, was about half-restored after respiration for 1 hour in glucose saline. General depressants in vivo preserved much of the glycogen from loss on excision, but loss nevertheless occurred on beginning respiration at 37[degree]. Resynthesis was similar in 2.5 and in 10 mm glucose but less in 1 mm. After resynthesis, glycogen fell promptly when O2 was ex-cluded, but insulin and brief application of electrical pulses had little if any effect on glycogen level. The lactate of the tissue which had greatly increased post mortem, on respiration in vitro fell to levels akin to those in vivo, but remained greater than in saline. When electrical pulses were applied to the tissue, glucose began within a few seconds to be converted into lactate. Conversion was at the rate of 400 umoles of lactate/g/hour for the first 20 or 30 seconds, but slowed after about 40 seconds of pulses. If pulses were stopped while the tis-sue lactate was still increasing, the increase continued for some seconds. The maximal transitory rates of formation of lactate and of inorganic phosphate on applying pulses to the tissue were similar, and were also close to that of the formation of labile phosphates potentially associated with the observed increase in respiration. Lactate forma-tion with continued pulses fell before glucose or phosphates were ex-hausted. An initial momentary glycolytic response to excitation is largely replaced by a subsequent, sustained increase in respiration.