AJP - Renal Physiology, Vol 251, Issue 3 485-F489, Copyright © 1986 by American Physiological Society
Effect of vasopressin on ependymal and capillary permeability to tritiated water in cat
G. A. Rosenberg, W. T. Kyner, J. D. Fenstermacher and C. S. Patlak
Ependymal cells line the cerebral ventricles forming the interface that
separates the cerebrospinal (CSF) and interstitial fluids (ISF).
Extracellular molecules move between ependymal cells, whereas lipid soluble
molecules pass both between and through cells. We measured the transfer of
tritiated water (TOH) from CSF to blood across the ependymal and capillary
interfaces by ventriculocisternal (VC) steady-state tissue clearance. Adult
cats anesthetized with pentobarbital sodium underwent VC perfusion with the
extracellular marker [14C]sucrose and TOH added to the artificial CSF.
Brain tissue was analyzed for depth of penetration of the isotopes into
periventricular gray matter. We found that TOH distribution space was lower
than expected from water content measurements, whereas sucrose space was
normal. Using VC steady-state equations we calculated an ependymal
permeability that was similar to the permeability of the cerebral
capillary. When arginine vasopressin (AVP) was added to the perfusate in
different amounts, both capillary transfer times and ependymal permeability
increased. Our results show that the ependyma may be important in water
movement in the brain and support the suggestion that AVP influences water
exchange in mammalian brain tissue.
