STUDIES ON THE TRANSPORT OF GLUTAMINE IN VIVO BETWEEN THE BRAIN AND BLOOD IN THE RESTING STATE AND DURING AFFERENT ELECTRICAL STIMULATION

Abstract— In this work we have studied the effect of afferent electrical stimulation (AES) of the contralateral brachial plexus on the release of glutamine and glutamate from the cat's brain into the cerebral venous blood, at rest and during continuous infusion of L-glutamine and sucrose solutions.
(1) In the resting state, before stimulation, there was a net outflow of glutamine from the brain into the cerebral venous blood, but no release of glutamic acid. (2) AES caused release of glutamate and increased 3.5-fold the release of glutamine. The increase in release of glutamine and glutamate was found to be reversed very shortly after stimulation. (3) Steady intravenous infusion of a 0.3 M-gluta-mine solution for 10 min changed the negative arterio-venous difference in glutamine to a positive one and increased the content in brain by 15×20%. In this case AES caused a singificant drop, to zero of the glutamine arterio-venous difference. (4) At the onset of pentamethylenetetrazole (PTZ) seizures, like AES, there was a significant reduction of the level of glutamine in the cats'cerebral cortex. This reduction vanished when the animals were infused with L-glutamine solution but not with 0.3 M-sucrose solution that was used as an inert electrolyte. (5) The kinetic behaviour of the glutamine transport is compatible with a carrier-mediated process, but not with passive diffusion.