LIGHT-INDUCED-CHANGES IN FROG PINEAL-GLAND N-ACETYLTRANSFERASE ACTIVITY

N-Acetyltransferase (NAT) activity was determined in the pineal gland of frogs (Rana tigrina) of different ages using 2-aminofluorene and p- aminobenzoic acid as substrates, and assayed by high-pressure liquid c hromatography. Frogs of different ages were either killed during the l ight phase or exposed to darkness or light for 1 min during the dark p hase of the lighting cycle, then returned to their cages in darkness f or 30 min before being killed. The pineal gland NAT activity of I-mont h-old frogs was inhibited when the animal was nocturnally exposed to 1 min of light. Nocturnal light exposure did not inhibit NAT activity i n 1-month-old frogs, even though these animal displayed clear light-da rk differences in pineal gland NAT activity. Nocturnal light exposure did not inhibit night-time levels of NAT activity in 1-month-old anima ls which. had been bilaterally enucleated, thus suggesting that this e ffect is retinally mediated. Pretreatment of 1-month-old and 6-month-o ld animals with isoproterenol (a beta-adrenoceptor agonist drug) preve nted the nocturnal light-induced inhibition of NAT activity. From the different sensitivity of 1-month-old and 6-month-old animals to differ ent intensities or durations of nocturnal light exposure it was found that the duration or intensity of light exposure was not able to inhib it nocturnal NAT activity. The NAT activity was at least 4-5-fold grea ter in 1 month-old frogs than in 6-month-old frogs. This is the first demonstration of the retino-pineal gland pathway that appears to produ ce light-induced changes in pineal glands of frogs 1-month-old or olde r, but this pathway only functions in I-month-old frogs, and does not appear to function in 6-month-old frogs. (C) 1997 Elsevier Science Ltd .