Diurnal variation in the requirement for RNA synthesis in the induction of pineal N-acetyltransferase

Abstract

There is a variable lag period in the induction of rat pineal serotonin - N-acetyltransferase activity by β-adrenergic stimulation, which increases with the duration of the animals' prior exposure to light. There is a similar variation in the lag period when enzyme activity is induced in culture by dibutyryl cyclic AMP. Experiments with actinomycin D indicate that RNA synthesis occurs during the lag period. If actinomycin D is added after the lag period, however, it does not reduce the level of N-acetyltransferase activity attained. Reinductions in glands from animals which have been in the dark for 6 hr have no lag period and do not require new RNA synthesis. The extent to which enzyme activity can be reinduced in culture in the presence of actinomycin D gradually increases during the first half of the night, when there is an increased release of norepinephrine from the nerve endings. These data suggest that RNA. presumably messenger RNA, that is necessary for increased. N-acetyltransferase activity, is synthesized and accumulates during the first half of the night. Thereafter, there appears to be a decline in the complement of RNA available for reinduction.