[The dissimilar effects of the single and prolonged administration of melatonin on the hypnogenic action of hexenal in mice in relation to the dose and the time of day].

At the acute administration the pineal hormone melatonin depending on the dose (0.01-10 mg/kg) potentiated the hypnogenic effect of hexenal (hexobarbital sodium) in mice both in the daytime and at night. When low doses of the hormone were chronically administered in the light phase of the day, there was noted a decrease of the duration of barbiturate anesthesia. A similar result was found during its round-the-clock evaluation against the background of 0.1 mg/kg of melatonin (a single dose) in the late daytime hours and on the contrary a sharp enhancement of hexenal action before switching on the light. The relationship between the circadian fluctuations of the hypnogenic effect of barbiturates and the periodical character of the epiphysis activity is suggested.