The melatonin generating system in the rat retina and pineal gland: effect of single and repeated electroconvulsive shock (ECS).

N-Acetyltransferase (NAT) activity peaks during the dark phase in the rat pineal gland.

• NAT shows a distinct circadian rhythm with low activity during the light phase and peak activity at night in the pineal gland and retina.
• Hydroxyindole-O-methyltransferase (HIOMT) does not exhibit significant diurnal variations in either the pineal gland or retina.
• Isoproterenol significantly increases NAT activity in the pineal gland when administered during the morning light phase, but not in the retina.
• Electroconvulsive shock (ECS), particularly repeated treatments, significantly raises NAT activity in the retina while tending to decrease it in the pineal gland of isoproterenol-treated rats.
• ECS slightly increases nocturnally-stimulated NAT activity in the retina and decreases it in the pineal gland.

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