Regulation of lithium in cerebrospinal fluid of the cat by the choroid plexus isolated in situ
Yen, M.H.; Reed, D.J.
Archives Internationales de Pharmacodynamie et de Therapie 251(2): 217-227
1981
ISSN/ISBN: 0003-9780 PMID: 7283549 Document Number: 176755
The role of the choroid plexus in regulating the lithium concentration in c.s.f. was studied by the use of the cat choroid plexus isolated in situ in a chamber. LiCl solution (154 mM) was infused i.v. to produce plasma lithium concentrations between 0 and 7.5 m-equiv/l. Over this range of plasma values the c.s.f./plasma ratio remained at 0.58. The plasma and c.s.f. concentrations were constant after about 90 min. Lithium (1.8 or 4.5 m-equiv/l.) was added to the artificial c.s.f. placed in the chamber at the start of a 30-min collection period. The lithium concentration in the chamber fluid was measured at the end of the collection period with the plasma concentration either 0 or greater than that in the chamber. When the lithium gradient was from chamber fluid to blood there was a net loss of lithium from the chamber and the amount was proportional to the gradient. However, when the gradient was in the opposite direction lithium was added to the chamber but the amount added was related to the plasma lithium concentration rather than to the blood-c.s.f. gradient. Altering the potassium concentration in the chamber fluid changed the rate of potassium transport without a comparable effect on lithium movement out of the chamber. Lithium transport by the potassium transport system does not appear to be a major factor in the loss of lithium from the chamber. The data suggest that lithium is transported actively across the choroid plexus into the c.s.f. by the system that is responsible for c.s.f. secretion. Movement from c.s.f. to blood appears to be accomplished primarily by passive diffusion when the c.s.f. concentration significantly exceeds that in the plasma.