Investigation of Circadian Rhythms for Pineal 5‐Hydroxytryptophol and Other Indoles in the Rat

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Abstract
5-Hydroxytryptophol (5HTL) occurs in the pineal gland of the rat at levels comparable to those of melatonin, yet few studies have been conducted to investigate 5HTL as a potential alternative pineal hormone. In this study the pineals of 90-day-old male Sprague Dawley rats have been assayed by high performance liquid chromatography coupled with electrochemical detection. Significant (P < .0001) circadian variation was measured in 5HTL levels, and a fivefold plateau elevation occurred during the middle of the light period. By comparison with the timing of the variations in N-acetyl serotonin and melatonin levels, it is suggested that 5HTL may not be regulated by simple competition with N-acetyl transferase for the common substrate 5HT but may, in fact, be regulated independently. Literature supporting such a suggestion, and a model incorporating it, are presented for discussion.