XXXX transport and metabolism in the central nervous system.

@entity21410 @entity95 @entity73215 @entity48400
The mechanisms by which @entity21410 (PA) enters and leaves brain, choroid plexus, and cerebrospinal fluid (CSF) were investigated by injecting [3H]PA either intravenously or intraventricularly into adult @entity95 . @entity48400 , either alone or together with unlabeled PA, was infused at a constant rate into conscious @entity95 . At 180 min, @entity48400 readily entered CSF, choroid plexus, and brain. In brain, CSF, and plasma, greater than 90% of the 3H was associated with [3H]PA. The addition of 200 mumol/kg PA to the infusion syringe decreased the penetration of @entity48400 into brain and CSF by approximately 70%. Two hours after the intraventricular injection of @entity48400 , @entity48400 was rapidly cleared from the CSF by a probenecid-sensitive mechanism. No metabolism of the @entity48400 occurred in brain. However, 18 h after the intraventricular injection of 37 microCi (34 nmol) of @entity48400 , approximately 40% of the 3H remaining in forebrain was converted to @entity73215 . These results show that PA enters and leaves CSF and brain by saturable transport systems. However, @entity48400 is very slowly converted to @entity73215 in brain in vivo.
