Pineal enzymes in chickens: Development of daily rhythmicity

Pineal serotonin N-acetyltransferase activity and HIOMT (hydroxyindole- O-methyl-transferase) activity were measured in chicks (White Leghorn Gallus domesticus) over a period of 8 weeks from the day of hatching. The measurements were made at two time points on selected days: one time point was taken during the light portion of the birds' environmental lighting regime, the other point was taken during the dark portion (1000 and 1600, respectively, in an LD12 : 12 cycle with lights-off at 1200 and lights-on at 2400). There were no dramatic differences in HIOMT activity between the light and dark measurements on any day, though the enzyme activity rose steadily with age. Changes were always seen in N-acetyltransferase activity in light versus dark. Dark-time N-acetyltransferase activity was higher than light-time activity. This includes the initial exposure of the chicks to dark on day 2 after hatching. N-acetyltransferase activity was also measured in the pineal glands of chick embryos kept in LD12 : 12. In embryos incubated for 17 and 19 days the dark-time values for enzyme activity were almost twice the light-time values.