In vitro uptake and metabolism of [3H]indole compounds in the pineal organ of the pike. I. A radiochromatographic study.

Thin layer chromatography analysis of [3H]serotonin and [3H]melatonin metabolites synthetized in vitro by the pineal organ of the pike was performed. After a 10-min pulse, [3H]serotonin was mainly converted into [3H]-5-hydroxyindoleacetic acid (37%), [3H]-5-hydroxytryptophan and [3H]-5-methoxytryptophan (12 to 14%), and [3H]-5-hydroxytryptophol and [3H]-5-methoxytryptophol (3.5 and 9%) at the onset of darkness. When the pulse was followed by postincubations (in a cold medium) of increasing duration (15, 30, and 60 min), it appeared that the amount of [3H]-5-hydroxyindoleacetic acid decreased, that of [3H]-5-hydroxytryptophol decreased faster than that of [3H]-5-methoxytryptophol, and the amounts of [3H]-5-hydroxy- and [3H]-5-methoxytryptophan increased. [3H]-N-acetylserotonin, [3H]melatonin, and [3H]-5-methoxytryptamine were found in very low amounts. At the beginning of the photophase or at the onset of darkness, the uptake and metabolism of [3H]melatonin (after a 10-min pulse followed by a 10-min incubation in cold medium) resulted mainly in the formation of [3H]-5-methoxytryptophol (23 to 43%) and of [3H]-5-methoxytryptamine (6 to 12%). These results show that the pike pineal organ can synthesize all indoles that are known in the pineal gland of higher vertebrates. Usual, but also unusual, pathways of the indole metabolism were found that will need further clarification. Among these are the possible carboxylation of serotonin and deacetylation of melatonin (leading to the synthesis of 5-methoxytryptophol). Altogether, the results obtained suggest that the indole metabolism might be more complex than what has already been described in vertebrates.