Correction of CSF HCO(-3) after its experimental increase in normocapnia. Role of plasma HCO(-3).

In anesthetized normocapnic dogs CSF [HCO(-3)] was increased to 33 mmol/l by perfusing the brain ventricles for 45 min with a mock CSF containing a high [HCO(-3)]. In dogs with normal plasma [HCO(-3)], CSF [HCO(-3)]fell by ca. 7 mmol/l in 2 h following the end of the perfusion. Lowering plasma [HCO(-3)] to 11 mmol/l by infusing HCl intravenously was without effect but increasing plasma [HCO(-3)] to 36 mmol/l by infusing Na2CO3 limited the CSF [HCO(-3)] fall to 2.8 mmol/l. It is concluded that correction of CSF [HCO(-3)] is partially dependent on a sufficiently low plasma [HCO(-3)]. The small and persistent fall of CSF [HCO(-3)] which at high plasma [HCO(-3)] occurs against a concentration gradient with blood suggests moreover the contribution of more specific mechanism(s) for lowering CSF [HCO(-3)] after its experimental increase.