Ovine Pineal Indoles: Effects of l-Tryptophan or l-5-Hydroxytryptophan Administration |
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| Authors: | David Sugden M A A Namboodiri David C Klein Richard K Grady Jr † Ivan N Mefford† |
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| Institution: | Section on Neuroendocrinology, Laboratory of Developmental Neurobiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, U.S.A.;Department of Chemistry, Boston College, Chestnut Hill, Massachusetts, U.S.A. |
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| Abstract: | L-5-Hydroxytryptophan (L-5-HTP) (20 or 200 mg/kg i.p.) but not L-tryptophan (500 mg/kg i.p.) loading substantially increases serum melatonin in sheep. In the present study we examined the effects of these compounds on pineal serotonin and six serotonin metabolites. L-Tryptophan failed to increase 5-hydroxytryptamine (5-HT; serotonin) or any of its metabolites despite a five-fold increase in pineal tryptophan. In contrast, L-5-HTP loading produced a marked increase in pineal 5-HT and its metabolites, including N-acetylserotonin (NAS) and melatonin, indicating that an increased synthesis of melatonin is responsible for the increased serum melatonin concentration after loading with this precursor. No change in pineal indoleamine N-acetyltransferase (NAT) activity was seen. These results are consistent with the suggestion that, during daytime in the sheep, 5-HT availability may limit the production of melatonin. |
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| Keywords: | 5-Hydroxytryptophan Serotonin l- Tryptophan Ovine pineal indoles |
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