Volume flow across choroidal ependyma of the rabbit

Abstract

Venous blood obtained by micropuncture from the principal draining vein of the choroid plexus was compared with mixed arterial blood and with artificial bathing solutions. During secretion into a bath approximately isoosmolal with plasma there was no significant difference between thawing points of mixed arterial and choroidal venous plasma, nor did a difference develop when the transependymal volume flow was speeded by isoosmolal replacement of electrolytes by nonelectrolytes in the bath. A net volume flow continued into a quite hypotonic bath (1/2 Tyrode). A coefficient of osmotic flow of .28 x 10-11 cm3/dyne sec was estimated when the added solute was sucrose. Solute and volume flows were uncoupled under the influence of acetazolamide, a hypertonic secretion at a reduced rate being the invariable result.