Micropuncture evaluation of the importance of perivascular pH for the arteriolar diameter on the brain surface

A micropipette technique was used to induce local changes of the bicarbonate concentration of the cerebro-spinal fluid surrounding arterioles on the exposed cerebral cortex of anaesthetized rats and cats. Injection volumes of a few nanoliters caused circumscribed and pronounced changes of the diameter of the arterioles under study: mock spinal fluid without bicarbonate dilated, while a solution containing 25 meq/l of bicarbonate constricted the vessels. In such experiments the localpCO2 of the arteriolar wall remains practically constant, since it is set by thepCO2 of the arterial blood and of the cerebral tissue. Hence the microinjections essentially consisted in a local change of the pH of the fluid surrounding a small segment of a cerebral arteriole. Since metabolic changes of the nervous tissue changes the periarteriolar pH, it is probable that local pH induced vasomotor changes of the type reported here participate in the so called metabolic regulation of the cerebral blood flow which underlies the local adaptation of the cerebral blood flow to changing functional demands.