title: Diabetes attenuates the inhibitory effects of endomorphin-2, but not endomorphin-1 on gastrointestinal transit in mice.
abstract: Diabetes affects the entire gastrointestinal tract from the esophagus to the anus. In the present study, the charcoal meal test was undertaken to evaluate and compare the effects of intracerebroventricular (i.c.v.) administration of endomorphins (EMs) on gastrointestinal transit in non-diabetic and diabetic mice. Significantly delayed gastrointestinal transit was found in both 4 and 8 weeks alloxan-induced diabetes compared to non-diabetes. Moreover, i.c.v. EM-1 and EM-2 dose-dependently delayed gastrointestinal transit in non-diabetes and diabetes. The EM-1-induced inhibitory effects of gastrointestinal transit in 4 weeks diabetes were qualitatively similar to those of non-diabetes. However, at higher doses, the EM-1-induced effects in 8 weeks diabetes were largely enhanced. Different to EM-1, the EM-2-induced inhibition of gastrointestinal transit in diabetic mice was significantly attenuated compared to non-diabetic mice. Moreover, these effects were further decreased in 8 weeks diabetes. The delayed gastrointestinal transit effects caused by EM-1 may be primarily mediated by μ2-opioid receptor in both non-diabetes and 4 weeks diabetes. Interestingly, in 8 weeks diabetes, these effects were mediated by μ2- and δ-receptors. However, the inhibitory effects of EM-2 were mediated by μ1-opioid receptor, which exerted a reduced function in diabetes. Also, poor blood glucose control might result in the attenuated effects of EM-2. Our present results demonstrated that diabetes attenuates the inhibitory effects of EM-2, but not EM-1 on gastrointestinal transit in mice. The different effects of EM-1 and EM-2 on gastrointestinal transit in diabetes may be due to changes of opioid receptor subtypes and their functional responses.
authors.affiliation: School of Life Science and Technology, State Key Laboratory of Urban Water Resource and Environment, Instrumental Science and Technology, School Electrical Engineering and Automation, Harbin Institute of Technology, 92 West Dazhi Street, Harbin 150001, China. Electronic address: wangcl@hit.edu.cn.
authors.forename: Chang-lin
authors.initials: CL
authors.lastname: Wang
authors.affiliation: School of Life Science and Technology, State Key Laboratory of Urban Water Resource and Environment, Instrumental Science and Technology, School Electrical Engineering and Automation, Harbin Institute of Technology, 92 West Dazhi Street, Harbin 150001, China.
authors.forename: Yu-xiang
authors.initials: YX
authors.lastname: Diao
authors.affiliation: School of Life Science and Technology, State Key Laboratory of Urban Water Resource and Environment, Instrumental Science and Technology, School Electrical Engineering and Automation, Harbin Institute of Technology, 92 West Dazhi Street, Harbin 150001, China.
authors.forename: Qiong
authors.initials: Q
authors.lastname: Xiang
authors.affiliation: School of Mechatronics Engineering, Harbin Institute of Technology, 92 West Dazhi Street, Harbin 150001, China.
authors.forename: Yu-kun
authors.initials: YK
authors.lastname: Ren
authors.affiliation: School of Life Science and Technology, State Key Laboratory of Urban Water Resource and Environment, Instrumental Science and Technology, School Electrical Engineering and Automation, Harbin Institute of Technology, 92 West Dazhi Street, Harbin 150001, China. Electronic address: guning@hit.edu.cn.
authors.forename: Ning
authors.initials: N
authors.lastname: Gu
mesh_terms: D000818:Animals; D003921:Diabetes Mellitus, Experimental / Q000503:physiopathology*; D005772:Gastrointestinal Transit / Q000187:drug effects*; D007328:Insulin / Q000494:pharmacology; D008297:Male; D051379:Mice; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology*; D011957:Receptors, Opioid / Q000378:metabolism
chemical_list: D007328:Insulin; D009292:Narcotic Antagonists; D009842:Oligopeptides; D011957:Receptors, Opioid; C105293:endomorphin 1; D009270:Naloxone; C105294:endomorphin 2
keywords: Diabetes; Endomorphins; Gastrointestinal transit; I.c.v. administration; Opioid receptors