Transport of choline out of the cranial cerebrospinal fluid spaces of the rabbit.

The role which carrier-mediated transport and passive diffusion play in the clearance of quaternary ammonium compounds from cerebrospinal fluid was evaluated by ventriculocisternal perfusion in rabbits by using [14C]choline as the primary test compound. Choline was transported out of cerebrospinal fluid by two processes: a saturable, carrier-mediated process with a Tmax of 70.5 ng/min and Kt of 2.2 microgram/min; and, a passive nonsaturable process with a cerebrospinal fluid perfusate clearance of 11.5 microliter/min. N1-methylnicotinamide depressed the clearance of choline as well as that of hexamethonium, suggesting that these cations share a common transport process. Ouabain reduced the clearance of choline and hexamethonium. Passage of choline into brain occurred by passive diffusion.