The effects of monoamine oxidase inhibitors on hypothermia produced in rats and rabbits by anaesthetics

Abstract

The effects of the monoamine oxidase inhibitors, tranylcypromine and phenelzine, were investigated on hypothermic responses occurring during anaesthesia in rats and rabbits. In rats pretreatment with tranylcypromine, injected either i.p., 2 or 10 mg/kg, or into the cerebral ventricles, 0.5 mg/kg, significantly increased hypothermic responses during both pentobarbitone and halothane anaesthesia. Pretreatment with phenelzine either i.p., 20 mg/kg, or intraventricularly, 1 mg/kg, also significantly increased the hypothermic responses during pentobarbitone or halothane anaesthesia. In rabbits, i.p. injection of tranylcypromine, 5 mg/kg, decreased pentobarbitone-induced hypothermia, but phenelzine, 20 mg/kg, i.p., failed to produce any significant change in the response to pentobarbitone. Injected into the cerebral ventricles tranylcypromine, 1 mg/kg, significantly increased the hypothermic response to pentobarbitone. In none of the animals in these experiments was a reversal of anaesthetic-induced hypothermia seen after pretreatment with MAO inhibitors. These results are in contrast to those previously reported in the cat and can be interpreted in terms of Feldberg's view of the temperature-regulating roles of hypothalamic NA and 5-HT and their release by anaesthetics. However, the possibility that the anaesthetics and MAO inhibitors may be acting at sites in the central nervous system other than the hypothalamus cannot be excluded.