In Vitro Uptake and Metabolism of [³H]Indole Compounds in the Pineal Organ of the Pike. I. A Radiochromatographic Study

Abstract

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.

Rhythmic Melatonin Biosynthesis in a Photoreceptive Pineal Organ: A Study in the Pike

“…responsible for the biosynthesis and storage of indole com pounds [9,10,12,[15][16][17][18][19][20][21][22][23][24], These properties were not shared by the other pineal cell types (interstitial cells and secondorder neurons). Similar conclusions have been recently de rived from studies in the goldfish pineal organ, where only cone-like photoreceptors have been described [37].…”

Pineal organs in deep demersal fish

“…It may contain an endogenous oscillator (Falcón et al 1989), although, under physiological conditions, photic signals dominate the control of indolamine hormone synthesis and release by the pineal photoreceptors (Falcón et al 1987;Bolliet et al 1995;Cahill 1996). Thus, melatonin synthesis is high during darkness and suppressed during the light phase (Gern et al 1978;Falcón et al 1985;Kroeber et al 2000). Because of the inhibitory effect of melatonin on gonadal volume and activity, the length of the light/dark period can control reproductive activity and synchronise it to the seasonal cycles (for a review, see Ekström and Meissl 1997).…”

Solubilization and Biochemical Characterization of the Melatonin Deacetylase from Xenopus laevis Retina

“…This melatonin clearance mechanism is therefore highly conserved and a very important component of melatonin metabolism within the nonmammalian vertebrate eye. A melatonin deacetylating activity may exist also within the vertebrate pineal gland (Falcon et al, 1985), although its functional significance there is unknown.…”