Rumen-Protected 5-Hydroxytryptophan Improves Sheep Melatonin Synthesis in the Pineal Gland and Intestinal Tract

Abstract

Background Based on the extensive biological effects of melatonin (MLT), it is beneficial to increase the MLT content in the bodies of animals at a specific physiological stage. This study was conducted to investigate the effect of a diet supplemented with rumen-protected (RP) 5-hydroxytryptophan (5-HTP) on the pineal gland and intestinal tract MLT synthesis of sheep. Material/Methods Eighteen Kazakh sheep were assigned randomly to 3 diet groups: control group (CT, corn-soybean meal basal diet), CT+111 group (111 mg/kg BW RP 5-HTP), and CT+222 group (222 mg/kg BW RP 5-HTP). The gene expressions of aromatic amino acid decarboxylase (AADC), arylalkylamine N -acetyltransferase (AA-NAT), hydroxyindole- O -methyltransferase (HIOMT), monoamine oxidase A (MAOA), and the intermediates of MLT synthesis were observed from the pineal gland and intestinal tract by the reverse transcription (RT)-PCR method. The 5-HTP, 5-HT, N -acetylserotonin (NAS), MLT, and 5-hydroxyindole acetic acid (5-HIAA) contents in the pineal gland and intestinal tract were analyzed by ultra-high-performance liquid chromatography–tandem mass spectrometry. Results The study showed that the pineal gland HIOMT expression ( P <0.05), MLT ( P <0.05) and 5-HIAA ( P <0.05) levels in the 222 mg/kg group significantly increased compared to those in the CT and CT+111 mg/kg groups. In addition, the AADC ( P <0.01) and AA-NAT ( P <0.05) gene expression levels in the duodenum and jejunum were increased by the supplementation of RP 5-HTP. Conclusions Rumen-protected 5-hydroxytryptophan promoted melatonin synthesis in the pineal gland and intestinal tract during the natural light period.

Effects of Duodenal 5-Hydroxytryptophan Perfusion on Melatonin Synthesis in GI Tract of Sheep

“…This observation is consistent with previous reports. Studies have shown when sheep were orally given 111–222 mg/kg LBW (equivalent 5-HTP 50–100 mg/kg LBW) rumen-protected 5-HTP, it increased their jejunum, ileum, cecum, and colon mucosa and plasma 5-HTP concentrations; however, the dose they used was much higher than those used in this study [ 36 , 39 , 40 ]. It has been reported that high dose of 5-HTP intravenous administration (over 300 mg/d) leads to animal developing poisoning symptoms similar to 5-HT-induced toxicity [ 41 ].…”

“…While if the dose of 5-HTP was under 50 mg/d, no adverse effects were observed. Based on the results mentioned above, in the current study, 5-HTP doses selected were 10 and 50 mg/d which is 50–100 times lower than that used by Zhao et al [ 36 , 39 ]. This difference may be due to the bioavailability of 5-HTP by the different delivery methods.…”

“…Due to the uncertainty of Trp supply on melatonin production in sheep, we select the 5-HTP as the precursor to feed sheep and attempt to identify whether this treatment can improve the melatonin production in sheep. Indeed, we have found that feeding 5-HTP increases MT content of blood plasma from the jugular vein in sheep [36,37] which mainly reflects the pineal originated melatonin [9,38]. Few studies have investigated the effects of 5-HTP supply on the GI tract melatonin synthesis [39], especially, the different segments of GI tract.…”

5-Hydroxytryptophan (5-HTP): Natural Occurrence, Analysis, Biosynthesis, Biotechnology, Physiology and Toxicology

“…In sheep, the administration of 5-HTP substantially increases serum melatonin through a marked increase in pineal 5-HT and its metabolites, including N -acetylserotonin [ 126 ], whereas during the natural light period, a promotion of melatonin synthesis in the pineal gland and intestinal tract was found in rumen-protected 5-HTP [ 127 ]. In fetal lambs in late gestation, systemic infusion of 5-HTP during normoxia greatly increases the incidence of fetal breathing movements [ 128 ].…”

Supplementary Tryptophan Fed to Sows Prior to and after Farrowing to Improve Piglet Growth and Survival

“…In addition to serotonin, melatonin production may also increase when sows are supplemented with tryptophan. In sheep, tryptophan supplementation (222 mg/kg BW) increased melatonin production compared to no supplementation [ 18 ]. Melatonin has been shown to decrease oxidative stress, which indirectly increases umbilical blood flow, increasing nutrient and oxygen supply to the developing fetus.…”