AJP - Regulatory, Integrative and Comparative Physiology, Vol 246, Issue 4 533-R541, Copyright © 1984 by American Physiological Society
Intracranial volume adjustments and cerebrospinal fluid pressure in the osmotically swollen rat brain
J. E. Melton and E. E. Nattie
Acute dilutional hyponatremia (DH) (plasma [Na+] approximately equal to 110
meq/l over 3 h) was produced by intraperitoneal dialysis with distilled
water in pentobarbital-anesthetized rats with either closed (SC) or open
(SO) skulls. SO rats showed marked brain protrusion during DH, but the loss
of brain Na+ and Cl- and gain in brain water was the same as that seen in
SC rats. During DH, cerebrospinal fluid pressure (PCSF) rose five to six
times within 90 min postdialysis and then fell toward control values in
both SC and SO rats. This pattern did not correlate with changes in brain
water, suggesting that volume adjustments in another intracranial
compartment, possibly bulk CSF, are partially responsible for changes in
PCSF. The pressure-volume characteristics of the intracranial space, as
measured by the pressure-volume index (PVI), were unaffected by osmotic
brain swelling. Comparison of PCSF values observed during DH with values
predicted from PVI data showed that actual PCSF is, at most, half the
predicted value. This again suggests reduction of a nontissue intracranial
compartment, which, from relative size considerations, is probably bulk
CSF.
