Effect of halothane upon rabbit brain mitochondria

Induced enzyme release from synaptosomes by halothane

GABA-transaminase has been found to be released from rat brain synaptosomes by halothane in a dose-related manner. The releases of both GABA-transaminase and succinic semialdehyde dehydrogenase were increased with time. The release of other enzymes (creatine kinase, glutamate decarboxylase, aspartate transaminase, lactate dehydrogenase, and malate dehydrogenase) was less in magnitude and not related to the duration of incubation. Such observations suggested a specific event in the halothane-induced release of GABA-catabolizing enzymes. A suggestion linking mode of anesthetic action to a mitochondrial effect of volatile anesthetics was made.

Control of cerebral vascular smooth muscle during general anaesthesia

The effects of some general anaesthetics, for example thiopentone, Althesin (alphaxalone + alphadolone) and ketamine, on cerebral vascular smooth muscle are those which would be expected from their metabolic actions. With other anaesthetics, mainly those administered by inhalation, and especially the volatile agents, cerebral blood flow increases in excess of the metabolic activity, which is usually depressed to varying degrees. During general anaesthesia with any of these agents, responses to changes in arterial Pco2 or blood pressure are maintained. Furthermore, when seizure activity occurs during enflurane administration, there is a flow response to the associated metabolic stimulation. The time course of the flow response to the metabolically depressant drug Althesin has been measured in baboons and shown to be very rapid. Wtih this drug cerebrovascular resistance begins to increase within 2 s of its arrival in the brain. This rapid flow change occurs also after sympathetic denervation. Extracellular fluid pH of the cortex does not alter until after the initiation of the vascular smooth muscle response.