Nyctohemeral profile of type II thyroxine 5'-deiodinase activity in the pineal and Harderian glands of the swiss mouse

Type II thyroxine 5'-deiodinase activity in both pineal and Harderian glands of the swiss mouse were studied. We show that pineal 5'-deiodinase activity exhibits a nyctohemeral profile with a maximal peak value at 05.00 h coincident with that for pineal melatonin. However, no rhythm of 5'-deiodinase activity was found in the Harderian gland. These results suggest at least a common regulatory mechanism for type II thyroxine 5'-deiodinase and melatonin production, and probably, an interrelationship between these two metabolic pathways.