Comparison between blood and saline perfusion on the uptake of amino acids by choroid plexus of the sheep.

Abstract

Uptake by the isolated perfused sheep choroid plexus of labelled naturally occurring amino acids, and the analogue MeAIB (methyl amino isobutyric acid) was measured using the single-pass, indicator dilution method. The uptake (Umax) of natural amino acids at the blood face of the choroid plexus, relative to the extracellular marker mannitol, ranged between 26 and 47% when using a saline perfusate. However, when the perfusion fluid was changes to one containing whole blood, uptake of the leucine, phenylalanine, proline, aspartate glutamate and lysine were significantly reduced with Umax now between -1.6 and 19.5%. In contrast the uptake of alanine, glutamine and glycine remained high despite the change in perfusion fluid. All amino acids, which showed uptake from the blood, also demonstrated self-inhibition when an additional 1 mM of the same unlabelled amino acid was added to the perfusion fluid. This indicates saturation of a carrier-mediate uptake process. There was no detectable uptake of the amino acid analogue, MeAIB during perfusion with either medium, confirming the absence of the "A" type amino acid carrier system for which this analogue is specific.