SOME EFFECTS OF ENFLURANE ANAESTHESIA ON BIOGENIC MONOAMINES IN THE BRAIN AND PLASMA OF RATS

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Abstract
The effects of enflurane-air anaesthesia on brain 5-HT turnover rate, brain cate-cholamine concentrations and plasma catecholamine concentrations have been studied in rats. Enflurane 1.7%, administered for 30 and 90 min, resulted in an increase in the brain 5-HT concentration. The 5-HIAA concentration was normal during anaesthesia, but increased 24 hr following the period of anaesthesia. Anaesthesia apparently depressed the turnover rate of 5-HT in brain tissue, measured during steady-state kinetics by the inhibition of monoamine oxidase by pargyline and the blocking of acid transport by probenecid. Enflurane possibly potentiated the mono-amine oxidase inhibition produced by pargyline. When enflurane was administered at a concentration of 2.5% for 30 and 90 min significant increases in the brain 5-HT concentration resulted. The 5-HIAA concentration also increased significantly after 90 min anaesthesia. The dopamine concentration in brain increased during enflurane anaesthesia, but noradrenaline and adrenaline concentrations remained unchanged. The plasma catecholamine concentrations decreased as the concentration of the anaesthetic agent increased. Although convulsions or involuntary movements were not seen in the rats during enflurane anaesthesia, increased 5-HT concentration in brain may be associated with the central nervous system excitation observed visually and with e.e.g. in both experimental animals and human patients during deep enflurane anaesthesia.

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