Composition of cerebral fluids in goats adapted to high altitude.

We explored the ionic composition of cerebral interstitial fluid (cISF) in six unanesthetized goats at sea level (SL) and again after 5 days at a simulated high altitude (HA) of 4,300 m. By measuring net transependymal fluxes of HCO3-, Cl-, and lactate during ventriculocisternal perfusions with lactate-free artificial cerebrospinal fluid (CSF) with various [HCO3-] and [Cl-], we determined [HCO3-] and [Cl-] in the inflowing perfusate that produced zero flux, which are estimates of the concentrations of these ions in cISF. Ventilatory acclimatization to HA was established in the goats with alkaline shift in cisternal CSF pH. At SL zero flux of HCO3- and of Cl- occurred when [HCO3-] and [Cl-] in the perfusate were equal to those in CSF. At HA Cl- flux again was zero when [Cl-] in perfusate and in the goat's own CSF were equal; however, for HCO3-, zero flux occurred at HA when [HCO3-] in perfusate was significantly lower than in CSF. Mean transependymal washout of lactate was 16 times larger at HA than at SL. We conclude that at SL [HCO3-] and [Cl-] in CSF were the same as in cISF. In goats adapted to HA [Cl-] in cISF and in CSF were again equal, whereas [HCO3-] in cISF was lower and [lactate] presumably higher than in CSF. The fluid surrounding the central chemoreceptors appears to be more acidic in goats acclimatized to HA than at SL despite the alkalosis in cisternal CSF. This may contribute to ventilatory acclimatization to HA.