PROCEDURE FOR MEASUREMENT OF AMINO-ACID TRANSPORT FROM BLOOD TO BRAIN IN SMALL ANIMALS

The exponential plasma specific activity curve 2.5 to 12.5 min after injection (sc) of [14C]tyrosine was integrated and divided by time to obtain the mathematical relationship between the average equivalent specific activity S and the measured specific activity S in any individual animal. S is the constant, average value of S that is equivalent to the curvllinearly varying quantity that the body tissues are actually exposed to. Dividing the total brain radioactivity by S gave the tissue Tyr uptake U. The function dU dt is linear from 2.5 to 12.5 min and represents the rate of uptake of the amino acid. Incorporation into protein was similarly measured. Brain uptake of Tyr averaged 7.06, and the apparent protein incorporation was 1.99 nmol/g of brain per min. The γ-glutamyl cycle inhibitor l-methionine-RS-sulfoximine reduced total brain uptake of tyrosine by 42.8% and the apparent rate of protein incorporation by 39.0%. © 1978.