The effect of local changes in potassium and bicarbonate concentration on hypothalamic blood flow in the rabbit.

Blood flow has been measured locally in the hypothalamus of anaesthetized rabbits by measuring the clearance of small volumes (5‐20 mul.) of a mock cerebrospinal fluid solution containing 133Xe. The effect of varying the [K+] or [HCO‐3] of the 133Xe‐containing solution on local hypothalamic blood flow has been investigated. 2. There was an increase in local hypothalamic blood flow if the 133Xe‐containing solution was HCO3‐‐free; raising the [HCO‐‐3,] of the solution to 40 mM caused a fall in local blood flow. 3. There was an increase in local hypothalamic blood flow when 133Xe was injectedin a mock cerebrospinal fluid containing 10 or 20 mM‐[K+]. There was no significant change in blood flow if a K+‐free or a 40 mM [K+] solution was used. 4. The decrease in hypothalamic blood flow caused by injecting a 40 mM‐[HCO3] solution could be reversed by the addition of 20 mM [K+] to the solution. There was no further increase in blood flow if 20 mM‐[K+] was added to a HCO3‐‐free solution. 5. It is concluded that local blood flow in the hypothalamus changes as a result of variation in local [K+] as well as local [HCO‐3]. The changes in blood flow in the brain which accompany neuronal activity could be mediated by variation in local [K+].