Effect of acetazolamide and furosemide on the production and composition of cerebrospinal fluid from the cat choroid plexus.

The effect of acetazolamide and furosemide on choroid plexus (CP) production and electrolyte composition of cerebrospinal fluid (CSF) from the cat CP in situ was investigated. Both drugs decreased CSF production by the CP by 50--90% from a control rate of 0.53 microL . min-1 . mg-1 CP within 1.5--2.5 h after the start of drug treatment. The results were similar whether the drug was administered intravenously or applied directly to the CSF side of the CP. A number of experiments in which the effect of administering drugs via the chamber were studied were continued with the drugs removed by washing the preparation with drug-free artificial CSF and the responses measured. The results demonstrated that the effects of acetazolamide and furosemide were reversed during the 1st h following the washout. Both drugs decreased K concentration of nascent CSF when administered intravenously and furosemide also did so when administered on the CSF side of the CP. It is concluded from these and previous data that acetazolamide and furosemide markedly inhibit the transport mechanism(s) in the cat CP that are responsible for CP secretion which represents about 40--60% of the total CSF production and that K transport is also affected.

Composition of fluid obtained from choroid plexus tissue isolated in a chamber in situ.

1. A method was developed for isolating a segment of the choroid plexus of the lateral ventricle of the cat brain in a chamber in situ.2. A comparison of electrolyte and protein concentrations in serum, ultrafiltrate of serum, cisterna magna fluid, fluid accumulated in the chamber and fluid collected from the choroid plexus by another technique, demonstrates that the chamber fluid is a secretory product of the choroid plexus.3. The rate of fluid formation in the chamber was 0.4 mul. min(-1) mg(-1) of tissue, a value in good agreement with reports in the literature.4. The observation that the concentration of K(+) in choroid plexus fluid was lower than that in the serum ultrafiltrate suggests that K(+) is regulated by an active transport process at the choroid plexus.5. Significant correlation was found between electrolyte values and the protein content of the chamber fluid. This suggests that plasma is the probable source of the protein in the chamber fluid and that K(+) and probably Ca(2+) and Mg(2+) in c.s.f. are subject to active homoeostatic regulation by the choroid plexus.6. The technique described provides a new opportunity to study in detail the functional characteristics of the choroid plexus.