The involvement of GABA-transaminase in the blood-brain barrier to radiolabelled GABA.

The involvement of GABA-transaminase (GABA-T) in the blood-brain barrier to GABA was investigated using a sensitive radiotracer technique which allows measurement of tracer permeation as a cerebrovascular permeability-area product, PA. In Sprague-Dawley rats subjected to peripheral GABA-T inhibition and occlusion of hepatic circulation, chromatographic (TLC) analysis together with lyophylized plasma samples showed the radioactivity measured in brain parenchyma was derived from the permeation of unchanged [3H]GABA and not its blood-borne metabolites. Permeation (PA) of i.v. injected [3H]GABA was poor in all brain regions examined. Pretreatment of these rats with various compounds known to inhibit endothelial GABA-T activity did not cause any increased permeation of [3H]GABA into the brain. These results suggest that the poor permeation of GABA into the rat brain is unrelated to the activity of GABA-T at endothelial sites.