Transport of Prostaglandins and Other Eicosanoids by the Choroid Plexus: Its Characterization and Physiological Significance

Abstract

Choroid plexi from the lateral ventricles of rabbits, cats, and dogfish (Mustelus canis) were used to characterize the prostaglandin (PG) uptake process and to establish its kinetic parameters and substrate specificity. The apparent Kt for PGF2.alpha. transport by the rabbit choroid plexus was 20 .mu.M; the Jmax was 27 nmol g-1 min-1. The Ki of inhibition of PGF2.alpha. transport by PGE2 was 20 .mu.M; the Jmax of PGF2.alpha. transport was unaltered by PGE2. A concentration of p-aminohippuric acid of up to 1 mM did not appreciably affect the Kt or the Jmax of PGF2.alpha. transport. The rate of PGF2.alpha. accumulation by rabbit choroid plexus was reduced by incubation at 4.degree. C, under anaerobic conditions, in the absence of sodium or in the presence of ouabain, probenecid, or bromcresol green. The choroid plexi of all three species also accumulated thromboxane B2, PGI2, and 6-keto-PGF1.alpha., suggesting that most, if not all, eicosanoids are substrates for this transport system. It is concluded that the choroid plexus transport system satisfies all the criteria of an active, energy-dependent transport system and that this system functions effectively at concentrations of eicosanoids present in the ventricular system under normal or pathological conditions. Hence, this transport system must make an important contribution to the pharmacokinetics of eicosanoids within the brain.