[Diurnal variation in glucose utilization in the pineal body of the monkey]

We employed the quantitative 2-[14C]-deoxyglucose method (Sokoloff's method) to measure glucose utilization in the pineal gland of pubescent monkeys. Glucose utilization in the pineal was 80-110% higher in the nocturnal, awake animals compared to the rate of both groups studied in the nocturnal, awake animals with both eyes open and with light deprivation for three hours. Short term visual deprivation during the day was without effect on pineal glucose utilization. The diurnal variations in melatonin levels in blood and CSF, higher at night than during the day, are the result of corresponding changes in the rate of production and elaboration of melatonin in the pineal gland. The release of norepinephrine from the postganglionic fiber of the superior cervical ganglia controls the production of melatonin in the pineal by regulating the activity of serotonin-N-acetyltransferase. It was reported that electrical stimulation of SCG via sympathetic trunk increased the levels of serotonin-N-acetyltransferase in the pineal and that it also increased glucose utilization in the pineal. It is believed that metabolic increase in the pineal reflects increased activity in sympathetic terminals distributed throughout the gland which stimulate its increase in hormone production. The present results indicate that there is an elevation of pineal metabolic rate at a time when blood and CSF levels of melatonin are known to be elevated Our finding that short-term light deprivation during the day did not affect the pineal metabolic rate is consistent with the result by Reppert et al (1981) in which they found that exposure to darkness during the day does not result in an increase in CSF melatonin.