N-acetyltransferase in the chick retina

Summary

N-acetyltransferase activity (NAT) was measured in tissues of chicks exposed to light-dark treatments and to injections. The results support hypotheses of similar circadian rhythms in retinal and pineal NAT, regulation of retinal and pineal NAT by environmental lighting, and inhibition of retinal and pineal NAT by cycloheximide and isoproterenol.

• 1. NAT was measured in 20 tissues dissected from chicks kept in LD12∶12. NAT fluctuated from 0.5 to 2.3-fold in the tissues except for the pineal gland and retinas (6.9 and 4.2-fold, respectively).

• 2. Retinal and pineal NAT were high in the dark and low in the light in LD12∶12; the change was usually larger in the pineal gland (7 to 12-fold) than in the retina (3 to 6-fold), but the NAT of the two eyes taken together was at least 2/3 of that of the pineal gland.

• 3. The NAT daily change persisted in both the eyes and the pineal gland for at least 3 days of constant dark which is evidence that NAT has a circadian rhythm in both these tissues.

• 4. Unexpected dark-to-light transitions resulted in a plummet (in 1 h) of NAT in the retina (51%) and in the pineal gland (77%). Extension of the light into the dark-time likewise suppressed NAT in the retina (78%) and in the pineal gland (83%). NAT in the retina was refractory to stimulation by dark in the early light-time, similar to the pineal gland.

• 5. Isoproterenol injections lowered pineal (53%), but not retinal, NAT when the injection was subcutaneous; the injection lowered retinal (52%), but not pineal, NAT, when the injection was intraocular. Cycloheximide injections lowered both pineal (48%) and retinal (68%) NAT when the injection was intraocular, but only pineal NAT (70%) when the injection was subcutaneous.