Effect of hyperoxia on histamine metabolism in rat brain synaptosomes: preliminary observations

Adult male Wistar rats were submitted to normobaric hyperoxygenation for 1 and 4 hours, then brain synaptosomes were isolated and uptake and release of the histamine precursor - histidine (His), histamine (HA) level and His metabolizing enzymes activities were measured. This uptake in hyperoxic synaptosomes was inhibited by about 20%. After 1-hour hyperoxia, a tendency towards an increase of the HA level, but a significant increase histidine decarboxylase (HD) and histamine methyltransferase (HMT) activities were observed. Four-hour hyperoxia caused a decrease of both the HA level and the activities of both enzymes, especially HMT. The changes were reversed in 1-hour posthyperoxic recovery, except for histidine uptake which remained inhibited.