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Tryptophan loading increases daytime serum melatonin levels in intact and pinealectomized rats
K Yaga1, R J Reiter, B A Richardson
1Department of Cellular and Structural Biology, University of Texas Health Science Center, San Antonio 78284-7762.
Life Sciences
|January 1, 1993
Summary
Oral L-tryptophan (L-Trp) significantly increases serum melatonin in rats, regardless of fasting status. This suggests extrapineal sources contribute to elevated melatonin levels after L-Trp administration.
Area of Science:
- Biochemistry
- Endocrinology
- Pharmacology
Background:
- Melatonin, a key hormone regulating circadian rhythms, is primarily synthesized in the pineal gland.
- L-tryptophan (L-Trp) is an essential amino acid and a precursor to serotonin and melatonin.
Purpose of the Study:
- To investigate the effects of L-tryptophan administration on serum and pineal melatonin levels in rats.
- To determine if the pineal gland is the sole source of increased serum melatonin following L-Trp supplementation.
Main Methods:
- Rats were administered L-tryptophan orally, with and without fasting.
- Serum and pineal melatonin levels were measured.
- Enzyme activity (NAT, HIOMT) and melatonin levels were assessed in pineal glands.
- Experiments were repeated in pinealectomized rats.
Main Results:
- Oral L-tryptophan administration led to a 4-fold increase in serum melatonin in both fasted and non-fasted rats.
- No significant changes were observed in pineal gland enzyme activity (NAT, HIOMT) or melatonin levels.
- L-tryptophan administration caused a substantial increase in serum melatonin even in pinealectomized rats.
Conclusions:
- The increase in serum melatonin following L-tryptophan administration is not solely dependent on the pineal gland.
- Extrapineal organs likely play a significant role in producing melatonin in response to L-tryptophan.
- These findings challenge the traditional view of the pineal gland as the exclusive source of circulating melatonin.