AJP - Regulatory, Integrative and Comparative Physiology, Vol 232, Issue 1 45-R53, Copyright © 1977 by American Physiological Society
CNS, CSF, and extradural fluid uptake of various hydrophilic materials in the dogfish
J. D. Fenstermacher and C. S. Patlak
The distribution of 10 radioactively labeled materials from blood to CSF,
extradural fluid (EDF), telencephalon (cerebrum), medulla, and spinal cord
was studied in the dogfish shark. Plasma volumes, blood flows, and
blood-to-tissue or fluid-transfer half-times (t1/2) were calculated from
these distribution data. Blood-EDF exchange occurred at slow but similar
rates for all tracers. Urea uptake by the CSF was very rapid compared to
that of the other compounds and may be facilitated by a special mechanism.
The tissue plasma spaces of all three CNS regions were small (1.1-1.5%).
The calculated rates of tissue blood flow (in ml/g-min) were 0.11 for
telencephalon and medulla and 0.055 for spinal cord. Choroid plexus blood
flow was estimated to be 2.3 ml/g-min, a surprisingly high rate. Transport
between blood and tissue was most rapid for water ethylene glycol and
slowest for inulin. The tissue t1/2's of urea indicated that a significant
portion of this compound's net uptake by periventricaul brain tissue
occurred via the CSF.
