Acid‐Base Relations in Arterial Blood and Cerebrospinal Fluid of the Unanesthetized Rat

A technique is described for collection of arterial blood in unanesthetized rats and for removal of cisternal cerebrospinal fluid (CSF) after anesthesia in such a way that the acid‐base parameters can be considered to reopresent the unanesthetized state. In uninjected rats the plasma pH was found to be 7.47, the p CO 2 38.5 mm Hg and the plasma bicarbonate concentration 27.3 meq/1. When such rats were made acidotic or alkalotic by means of intraperitoneal injections of acid and basic solutions both the CSF bicarbonate concetration, and the CO 2 tension, varied linearily with the plasma bicarbonate concentration, but the changes in the CSF bicarrbonate concentrtion were only 35 per cent of the corresponding plasma changes. There were small but significant changes (0.04 pH units) of the CSF pH in the same direction as in blood and there was thus no indication of paradoxical shifts in the CSF pH. The implication of these findings for current theories regarding the regulation of respiration is discussed.