Abstract
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+].