Background: Glycyl-glutamine and glycyl-tyrosine may supply adequate glutamine and tyrosine in amino acid solutions for parenteral nutrition. However, plasma peptides may be transported into the cerebrospinal fluid, exerting effects on the neuronal tissue. Cerebrospinal fluid (CSF) and plasma amino acid concentrations after administration of a glycyl-glutamine/glycyltyrosine supplemented amino acid solution were therefore evaluated in a randomized controlled comparison with a conventional amino acid infusion.
Methods: Dipeptide/amino acid solutions (0.60 mL/h/kg; 82.2 mg total dipeptides/amino acids/h/kg) or conventional amino acid solutions (0.73 mL/h/kg; 83.2 mg total amino acids/h/kg) were infused in 15 patients per group scheduled to undergo spinal anesthesia for urologic surgery over a 12-hour period preoperatively. Plasma amino acids were measured before the infusion was started. CSF and venous concentrations were analyzed simultaneously before the infusion was stopped. CSF samples were drawn through the spinal needle for anesthesia.
Results: The dipeptide-containing solution did not increase either dipeptide to detectable levels in the CSF (detection limit < 5.0 nmol/mL). Venous glycyl-glutamine increased from below detection limits up to 308 +/- 111 nmol/mL (p < .05), whereas glycyl-tyrosine could not be found. In the dipeptide group, venous glutamine and tyrosine were higher (p < .05) but only tyrosine appeared in small amounts (p < .05) in the cerebrospinal fluid.
Conclusions: This study provides no evidence to support a CSF entry of IV glycyl-tyrosine and glycyl-glutamine under conditions of a normal blood-brain barrier in the adult (detection limit 5 nmol/mL). The data suggest that amino acid solutions containing these dipeptides may be used in parenteral solutions for nutrition support.