Exchange of albumin between blood, cerebrospinal fluid, and brain in the cat

Abstract

The exchange of albumin between blood, cerebrospinal fluid, and brain was studied in cats during steady-state ventriculocisternal perfusion. Cat serum albumin-131I was added to the perfusion fluid or given intravenously. When albumin-131I was added to the perfusion fluid, its clearance was dependent on bulk absorption of cerebrospinal fluid. It was never greater that inulin clearance, and it was independent of the protein concentration (7 [mu]g-3 mg/ ml). Less than 0. 1% of the radioactivity could be recovered from the brain. When albumin-131I was given intravenously, the average amount of this protein entering the ventricular system was 1. 32 [mu]g/min. In these experiments, the ratio of specific activities of cerebrospinal fluid-to-serum albumin approached unity between 4 and 20 hr after injection. The reduction of cerebrospinal fluid formation by acetazolamide resulted both in a decrease of albumin influx to an average of 0. 77 [mu]g/min and in a decrease in the specific activity of albumin from 0. 81 to 0. 35. This suggests that transfer of albumin from blood to cerebrospinal bluid is only partially dependent on bulk fluid formation; a portion of the albumin probably enters from the surrounding nervous tissue.