The activity of pineal serotonin-N-acetyltransferase (NAT) was compared in four mammalian species: the albino rat, the golden hamster, the Mongolian gerbil and the English short-hair guinea pig. In all species a night-time elevation in pineal NAT activity was apparent. In the rat, pineal NAT activity exhibited a dark:light ratio of 60:1; in the hamster and gerbil the ratio was 3:1 while in the guinea pig the dark:light ratio was 1.5:1. With the exception of the guinea pig, the greatest pineal NAT activity was recorded at 04.00 h (8 h after onset of darkness). In the guinea pig the maximal NAT activity was attained at 24.00 h (4 h after onset of darkness).
ASJC Scopus subject areas