Neuroscience Letters 384 (2005) 7–10 Cerebral interstitial levels of glutamate and glutamine after intravenous administration of nutritional amino acids in neurointensive care patients Elisabeth Ronne Engstr ¨ om a,∗ , Lars Hillered a , Per Enblad a , Torbj¨ orn Karlsson b a Department of Neurosurgery, Uppsala University Hospital, 751 85 Uppsala, Sweden b Department of Anesthesiology, Uppsala University Hospital, Uppsala, Sweden Received 8 February 2005; received in revised form 6 April 2005; accepted 11 April 2005 Abstract After severe trauma or disease glutamine (GLN) is mobilised from all muscles, including the heart and smooth muscles. The result is weakness and fatigue which affects recovery. The breakdown of muscle tissue can be counteracted by external GLN supply. There are concerns, however, that increasing the blood glutamine (Blood-GLN) concentration in patients with acute brain diseases is harmful by elevating the CNS interstitial (IS) concentration of glutamate (CNS-GLT), and that this may result in a secondary excitotoxic injury. We therefore studied the IS CNS-GLN and CNS-GLT when a commercially available nutritional amino acid solution was given intravenously. Ten NICU patients were included. The IS concentrations of amino acids in the brain were measured using intracerebral microdialysis. Blood concentrations of amino acids were measured before and after the amino acid infusion. The change in Blood-GLN was 2.14 (median; range 1.34–3.22) times the basal levels and Blood-GLT increased 1.37 (median; range 0.93–3.45) times basal levels. Both changes were statistically significant. The changes in CNS-GLN was 1.21 (median; range 0.72–1.92) and for CNS-GLT 0.96 (median; range 0.45–1.53) times the basal levels. This was statistically significant for CNS-GLN but not for CNS-GLT. A high initial CNS-GLT (55.3 mol/l) in one patient increased even further to 84.4 mol/l after infusion of amino acid solution. We submit that nutritional amino acid solutions can be administrated to some patients with acute brain disease without increasing the CNS-GLT values. However, since BBB function was not quantified in our study, further evaluation of this issue is warranted. © 2005 Elsevier Ireland Ltd. All rights reserved. Keywords: Glutamine; Glutamate; Microdialysis; Neurointensive care Glutamine (GLN) is the most abundant amino acid in the body comprising 60% of the free intracellular amino acids in mus- cle tissue [2]. GLN acts as an energy fuel for rapidly prolifer- ating cells (fibroblasts, immune and gastrointestinal cells). It is also a donor of nitrogen in the synthesis of purines, pyrim- idines, and nucleotides, a modulator of protein metabolism and a precursor for urea and ammonia synthesis [22]. The synthesis of GLN is also probably a factor in the acid–base control [1]. The body’s pool of GLN is mainly synthesised in the liver, in amounts normally covering the daily metabolic need. After trauma or disease there is a general catabolism of the tissues in the body including an increase in protein turnover [13]. In this ∗ Corresponding author. Tel.: +46 18 6114990; fax: +46 18 558617. E-mail address: elisabeth.ronne.engstrom@akademiska.se (E. Ronne Engstr ¨ om). process GLN together with other amino acids is mobilised from all muscles including the heart and smooth muscle. The efflux of glutamine from muscular tissues in critical illness serves as an important carrier of ammonia (nitrogen) to the splanchnic area. The result of this catabolism is long-term weakness and fatigue adversely affecting rehabilitation and recovery. Recent publications show that the breakdown of the mus- cles may be diminished if external GLN supply is given [10,15]. Apart from enteral administration of GLN this is made possible by GLN-containing dipeptides commer- cially available for parenteral administration. There is ev- idence from different studies that external GLN supply is beneficial in association with surgical procedures [8,9] as well as to patients with brain injury [7]. GLN-containing nutrition is therefore now given routinely to critical care patients. 0304-3940/$ – see front matter © 2005 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2005.04.030