Preliminary investigations of melatonin and 5-methoxy-tryptophol synthesis in the pineal, retina, and harderian gland of the mole rat and in the pineal of the mouse "eyeless".

Hydroxyindole-O-methyltransferase (HIOMT) activity for the synthesis of melatonin and 5-methoxytryptophol, both 5-methoxyindoles, was measured in the pineal, the Harderian gland and the retina of the mole rat and in the pineal of the mouse "eyeless". In the pineal and the Harderian gland of the mole rat a larger amount of 5-methoxytryptophol than of the melatonin is synthesized. 5-Methoxyindole synthesis is extremely high in the Harderian gland, whereas in the retina HIOMT activity is low and variable. In the pineal of the mouse "eyeless", a low 5-methoxyindole synthesis showing no circadian rhythm is demonstrated. It is concluded that, besides the generally accepted regulation of the indole metabolism by light, in species with atrophied eyes having Harderian glands (mole rat) and in species without eyes other factors than light might be responsible for the indole metabolism in the pineal gland.