Inhibited hypothalamic histamine metabolism during isoflurane and sevoflurane anesthesia in rats

Histamine is most densely distributed in the hypothalamus and has an important effect on consciousness or wakefulness. It has been little considered whether general anesthetics could exert their effects on hypothalamic histamine metabolism. The present study was conducted to investigate the effects of isoflurane and sevoflurane anesthesia on hypothalamic histamine metabolism.

Sixty male Wistar rats were divided equally into isoflurane and sevoflurane anesthesia groups. Each group was divided into three equal sub-groups: the control, anesthesia and recovery groups. The rats of the anesthesia and recovery groups were exposed to either 2% isoflurane or 3% sevoflurane for 30 min. The recovery group was kept in air for 30 min after anesthesia. The rats were decapitated to dissect out hypothalamus which was divided into the fore and rear portion. The contents of histamine and 1-methylhistamine, which is a main histamine metabolite, were determined by high-performance liquid chromatography. The obtained data were analyzed by one-way analysis of variance followed by Bonferoni's test.

Histamine contents of the anterior and posterior hypothalamus in both isoflurane and sevoflurane groups increased significantly during the anesthesia and 1-methylhistamine contents of the anterior and posterior hypothalamus in sevoflurane group increased remarkably after anesthesia. The increases of histamine contents supposedly reflected inhibited histamine metabolism and the increases of 1-methylhistamine would be caused by acceleration of histamine degradation.

Histamine metabolism was inhibited during both isoflurane and sevoflurane anesthesia and accelerated only in the posterior hypothalamus during the emergence from these anesthetics.