| ObjectiveTo study the effect of the novel melatonin receptor agonist Neu-p11 on glucolipidmetabolism in model rats of type 2 diabetesand the mechanism mediated by HPA axis. To open up a new way for the treatment of T2 DM.Methods72 male Wistar rats were used and 9 of them were randomly selected as normal control group received a regular diet of rat chow, and the rest rats were given high-fat diet combined with injection of small dose of streptozotocin(STZ). Type 2 diabetic model rats, which blood glucose value were more than or equal to 11.1mmol·L-1, were divided into model group(model) and melatonin group(MLT), and Neu-p11-high dose group(Neu-H),-medium dose group(Neu-M) and low-dose group(Neu-L) according to the level of blood glucose and body weight. Each group contains 8 rats. Control and model group were given 1ml·200g-1normal saline with same volume. MLT group were given 20 mg·kg-1 melatonin. Neu-p11 group with high, medium, and low dose were given 20 mg·kg-1, 10 mg·kg-1 and 5 mg·kg-1, respectively.The weight, food, water consumption were recorded daily. The fasting blood glucose(FBG)levels of rats were determined weekly; Emotional arousal and open-field tests were tested in rats on the 21 th and 35 th day; On the 7th, 21 th and 35 th day, the blood lipid levels including the total cholesterol(TC), triglyceride(TG) level, high density lipoprotein cholesterol(HDL-C), low density lipoprotein cholesterol(LDL-C) level in rats were assayed;Intaperitoneal glucose tolerance(IPGTT) test in rats was performed after 21 days administration; Insulin tolerance test(ITT) in rats was performed after 28 days administration;On the 35 th day the plasma insulin(INS) level in rats were measured;Corticotropin releasing hormone(CRH), adrenocorticotropic hormone(ACTH) and corticosterone(CORT) were measured on d7, d14, d35; On the 35 th day, the rats used to make pathological sections(5 rats with similar blood glucose values were selected from the model rats, which were randomly divided into model group, MLT group, Neu-H, Neu-M and Neu-L group given homologousdrugs, respectively. The rats were fed separately). After perfusion, the brain, liver, fat,pancreas, adrenal gland, spleen were soaked in 4% poly formaldehydeto make the pathological sections.The remaining rats were decapitated, the liver, bilateral kidneys, spleen and bilateraladrenal glands were removed, and theweighing and organ indexes were recorded.An appropriate amount of liver and muscle tissue were used to determine the content of the glycogen and the activity of hepatic glucose-6-phosphatase(G-6-Pase). The relative expression of liver glucocorticoid receptor(GR), glucose transporter-4(GLUT-4), peroxisome proliferator activated receptor gamma(PPAR gamma) m RNA, glucocorticoid receptor(GR)in hippocampal tissue, 11 beta hydroxysteroid dehydrogenase 1(11β-HSD1) m RNA and glucocorticoid receptor(GR) in adrenal tissue, MT1 and MT2 m RNA, as well as adipose tissue GR, adiponectin(Adipo), PPAR-γ, Leptin, m RNA GLUT-4 were detected by RT-PCR.The expression of GR, MT1 and MT2 proteins in rat liver, hippocampus, hypothalamus,pituitary and adrenal tissues were detected by Western Blot. The pathological changes of brain,adrenal gland, pancreas, liver and spleen were observed by HE staining methods.ResultsCompared with the normal group, the food and water gained in model rats were significantlyincreased(P<0.05). Body weight and the emotional arousal scores were tended to be decreased. FBG were increased significantly(P<0.01).The horizontal sports and vertical movement scores were significantly decreased, which reached 56.76%(P<0.01) and 57.24%(P<0.01), respectively. The central grid residence time were prolonged significantly to105.04%(P<0.05). The glucose and insulin tolerance were significantly impaired(P<0.05).The plasma TC and TG were increased significantly(P<0.05 or P<0.01). HDL-C were decreased significantly(P<0.05). LDL-C was intended to be increased and the glycogen content was decreased significantly(P<0.01), the content of glycogen increased, liver and kidney adrenal index increased significantly(P<0.01), the index of spleen were increased,liver G-6-Pase activity were increased significantly(P<0.01), d35 INS level showed an increased tendency. The ACTH and CORT levels of plasma ACTH and d7 were both increased. The d14 and d35 levels were decreased, theexpression of glucose, lipid metabolism and the related genes and protein of the HPA axis were impaired.Compared with the model group, the food uptake of MLT and Neu-p11 groups were all decreased, and in the first and third weeks of administration, the food uptake of MLT and Neu-p11 in different groups were significantly increased, respectively; The water gain of each group were decreased significantly;Weight and behavioral indicators were all improved;FBGwere decreased in each dose groups of Neu-p11, which showed significant difference on d14 and d35 respectively; Glucose tolerance, insulin tolerance, blood lipid, organ index, G-6-Pase activity and liver HPA axis hormone levels were all improved; GR m RNA relative expression level in liver, hippocampus and adipose tissue, MT1 and MT2 m RNA in adrenal tissue and PPAR-γ, GLUT-4, Adipom RNA in adipose tissue were significantly increased(P<0.05 or P<0.01); 11β-HSD1 m RNA in hippocampus and leptin m RNA in adipose tissue were significantly lowed(P<0.05 or P<0.01); The expression of GR in liver, hippocampus and tissues related to HPA axis were significantly increased(P<0.05 or P<0.01). And Neu-L could significantly decreasethe expression of MT1 and MT2 protein in the hippocampus(P< 0.05,P<0.01).ConclusionNeu-p11 can improvethe glucose and lipid metabolism in type 2 diabetes rats induced by high fat combined with small dose of streptozotocin. The mechanism may be related to the expression of glucose and lipid metabolism genes and proteins in liver, hippocampus,hypothalamus, pituitary, adrenal gland and adipose tissue, and the inhibition of HPA axis activity. |
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