The relative importance of perivascular supply and removal for amino acid turnover in ISF
Excluding glutamine, concentrations of each of the amino acids in CSF and ISF are usually < 1/5th of those in plasma (see below) and in total < 1 mM. With a perivascular clearance of 1 µL g−1 min−1, and an amino acid concentration at the high end of the observed range, 100 µM, the rate of loss or gain of any particular amino acid by the perivascular route is expected to be of the order of 0.1 nmol g−1 min−1 or less, which is likely to be negligible. Amino acid loss from the brain by outflow of CSF at 0.25 µL g−1 min−1 (500 mL day−1 for a 1400 g brain) at 100 µM would be 0.025 nmol g−1 min−1 which again is likely to be negligible.