1-ACYL-2-LYSOPHOSPHATIDYLCHOLINE TRANSPORT ACROSS THE BLOOD-RETINA AND BLOOD-BRAIN-BARRIER

The transport of lysophospholipids through the rat blood-retina and blood-brain barrier was determined by using radioactive 1-palmitoyl-2-lysophosphatidylcholine (Pam-lysoPtdCho) and by measuring the uptake of this labeled compound into the retina and various brain regions after short in situ carotid perfusion. The transport was not affected by probenecid (0.25 mM), but it was inhibited, in a dose-dependent manner, by circulating albumin which is able to bind tightly to lysophosphatidylcholine and lowered the availability of the latter for tissue extraction. Radiotracer transfer in the retina was higher than in brain regions. The permeability-surface area products (PS) changed with the inclusion of unlabeled Pam-lysoPtdCho, showing that transport across retinal and brain microvessels is mainly saturable. The data provided an estimate of transport constants (V-max, K-m and non-saturable constant K-d). However, we could not distinguish whether this saturable process represents the saturation of a transport carrier or simple passive diffusion followed by the saturation of enzymatic reactions. In brain tissue lipid extract, 20 s after carotid injection, radiolabel was associated by 45% to unmetabolized Pam-lysoPtdCho. Partial acylation to phosphatidylcholine, as well as hydrolysis and redistribution of the fatty acyl moiety into main phospholipid classes also occurred. The present results, compared to our previous data, indicate that Pam-lysoPtdCho is transported faster and/or in greater amounts than unesterified fatty acids.