title: Role of GLP-1 in the Hypoglycemic Effects of Wild Bitter Gourd.
abstract: This study aimed to examine the role of GLP-1 in the hypoglycemic activity of wild bitter gourd (Momordica charantia L., BG). In vitro, the GLP-1 secretion in STC-1, a murine enteroendocrine cell line, was dose dependently stimulated by water extract (WE), its fractions (WEL, >3 kD and WES, <3 kD), and a bitter compounds-rich fraction of BG. These stimulations were partially inhibited by probenecid, a bitter taste receptor inhibitor, and by U-73122, a phospholipase C β 2 inhibitor. These results suggested that the stimulation might involve, at least in part, certain bitter taste receptors and/or PLC β 2-signaling pathway. Two cucurbitane triterpenoids isolated from BG, 19-nor-cucurbita-5(10),6,8,22-(E),24-pentaen-3 β -ol, and 5 β ,19-epoxycucurbita-6,24-diene-3 β ,23 ξ -diol (karavilagenine E,) showed relative high efficacy in the stimulation. In vivo, mice fed BG diet showed higher insulinogenic index in an oral glucose tolerance test. A single oral dose of WE or WES pretreatment significantly improved intraperitoneal glucose tolerance. A single oral dose of WES significantly decreased glucose and increased insulin and GLP-1 in serum after 30 min. This acute hypoglycemic effect of WES was abolished by pretreatment with exendin-9, a GLP-1 receptor antagonist. Our data provide evidence that BG stimulates GLP-1 secretion which contributes, at least in part, to the antidiabetic activity of BG through an incretin effect.
authors.affiliation: Department of Biochemical Science and Technology, National Taiwan University, Taipei 106, Taiwan.
authors.forename: Ting-Ni
authors.initials: TN
authors.lastname: Huang
authors.forename: Kan-Ni
authors.initials: KN
authors.lastname: Lu
authors.forename: Yi-Ping
authors.initials: YP
authors.lastname: Pai
authors.lastname: Chin Hsu
authors.forename: Ching-Jang
authors.initials: CJ
authors.lastname: Huang