title: Peripheral serotonin enhances lipid metabolism by accelerating bile acid turnover.
abstract: Serotonin is synthesized by two distinct tryptophan hydroxylases, one in the brain and one in the periphery. The latter is known to be unable to cross the blood-brain barrier. These two serotonin systems have apparently independent functions, although the functions of peripheral serotonin have yet to be fully elucidated. In this study, we have investigated the physiological effect of peripheral serotonin on the concentrations of metabolites in the circulation and in the liver. After fasting, mice were ip injected with 1 mg serotonin. The plasma glucose concentration was significantly elevated between 60 and 270 min after the injection. In contrast, plasma triglyceride, cholesterol, and nonesterified fatty acid concentrations were decreased. The hepatic glycogen synthesis and concentrations were significantly higher at 240 min. At the same time, the hepatic triglyceride content was significantly lower than the basal levels noted before the serotonin injection, whereas the hepatic cholesterol content was significantly higher by 60 min after the injection. Furthermore, serotonin stimulated the contraction of the gallbladder and the excretion of bile. After the serotonin injection, there was a significant induction of apical sodium-dependent bile acid transporter expression, resulting in a decrease in the concentration of bile acids in the feces. Additionally, data are presented to show that the functions of serotonin are mediated through diverse serotonin receptor subtypes. These data indicate that peripheral serotonin accelerates the metabolism of lipid by increasing the concentration of bile acids in circulation.
authors.affiliation: Cellular Biology Laboratory, Graduate School of Agricultural Science, Tohoku University, 1-1 Tsutsumidori-Amamiyamachi, Aoba-ku, Sendai 981-8555, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Watanabe
authors.forename: Daisuke
authors.initials: D
authors.lastname: Akasaka
authors.forename: Hideki
authors.initials: H
authors.lastname: Ogasawara
authors.forename: Kan
authors.initials: K
authors.lastname: Sato
authors.forename: Masato
authors.initials: M
authors.lastname: Miyake
authors.forename: Kazuki
authors.initials: K
authors.lastname: Saito
authors.forename: Yu
authors.initials: Y
authors.lastname: Takahashi
authors.forename: Takashi
authors.initials: T
authors.lastname: Kanaya
authors.forename: Ikuro
authors.initials: I
authors.lastname: Takakura
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Hondo
authors.forename: Guozheng
authors.initials: G
authors.lastname: Chao
authors.forename: Michael T
authors.initials: MT
authors.lastname: Rose
authors.forename: Shyuichi
authors.initials: S
authors.lastname: Ohwada
authors.forename: Kouichi
authors.initials: K
authors.lastname: Watanabe
authors.forename: Takahiro
authors.initials: T
authors.lastname: Yamaguchi
authors.forename: Hisashi
authors.initials: H
authors.lastname: Aso
mesh_terms: D000818:Animals; D001647:Bile Acids and Salts / Q000097:blood / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005215:Fasting / Q000097:blood / Q000378:metabolism; D005704:Gallbladder / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D005947:Glucose / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism; D007082:Ileum / Q000187:drug effects / Q000378:metabolism; D007274:Injections, Intraperitoneal; D007328:Insulin / Q000097:blood / Q000378:metabolism; D050356:Lipid Metabolism / Q000187:drug effects* / Q000502:physiology; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D012701:Serotonin / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D001647:Bile Acids and Salts; D007328:Insulin; D012701:Serotonin; D006003:Glycogen; D005947:Glucose