Effects of halothane, pentobarbital and ketamine on serum melatonin levels in the early scotophase in New Zealand white rabbits.

In mammals, the nocturnal rise in pineal melatonin is regulated by signals from the endogenous clock, the hypothalamic suprachiasmatic nuclei. There have been few reports on whether anaesthetics which modulate multisynaptic neuronal functions affect melatonin secretion. We studied the effects of three commonly used anaesthetics, halothane, pentobarbital and ketamine, on serum melatonin levels in male New Zealand white rabbits. Seven blood samples were collected, 30-60 min apart, before, during and after anaesthesia. Experiments were performed in the late light and early dark period, so that changes in melatonin secretion would be reflected in the onset and/or level of nocturnal serum melatonin. Serum melatonin levels were determined by radioimmunoassay. Our results indicated that halothane attenuated the release of melatonin and pentobarbital had no apparent effect, whereas ketamine potentiated the release of melatonin. These findings suggest that melatonin levels may be affected in patients anaesthetized with halothane or ketamine, resulting in disturbed biological rhythms, especially the sleep-wake cycle following recovery.