Regulation of gluconeogenesis in liver, kidney and intestine by glucagon / 中国药理学通报

ABSTRACT

Aim To investigate the regulatory effect of glucagon on gluconeogenesis in liver, kidney and intes¬tine during different fasting periods and the underlying mechanism. Methods The 8-week-old male C57BIV 6J mice were randomly divided into six groups ( n = 6) :control group, control + glucagon group, fasting 18 h group, fasting 18 h + glucagon group, fasting 36 h group, and fasting 36 h + glucagon group. Glucose, triglyceride ( TG) and free fatty acids ( FFAs ) kits were used to detect their serum contents in mouse in-traperitoneal injection of glucagon at different fasting time points. Besides, liver/muscle glycogen assay kit and PAS staining were used to detect the glycogen con¬tents in liver tissue. RT-PCR method was used to observe the effects of glucagon on the gene expressions of peroxisome proliferators-activated receptor y coactivator la (PGC-1α), glucose-6-phosphatase (G6Pase) and phosphoenol pyruvate carboxykinase 1 (PEPCK) in liver, kidney and intestine of mice at different fasting time. Western blot was employed to detect the protein expressions of PGC-1α, G6Pase, PEPCK, phosphoryl-ase protein kinase A ( p-PKA) , protlein kinase A (PKA) , phosphorylase cAMp-response element binding protein (p-CREB) and cAMp-response element binding protein (CREB) in liver, kidney and intestine of mice were. Results (1) Glucagon increased the serum glucose level, reduced serum TG and FFAs levels, and reduced the hepatic glycogen content. (2) Glucagon promoted gluconeogenesis via upregulation of PGC-1α. On the stimulation of glucagon, PGC-1α gene and protein expressions in liver were significantly raised by glucagon when the mice were fasted 18 h and 36 h, while the gene and protein expressions of PGC-1α in kidney were obviously up-regulated by glucagon after fasting 18 h. However, PGC-1α gene and protein expressions in intestine were significantly elevated by glucagon at 36 h after fasting. (3 ) Glucagon induced gene and protein expressions of gluconeogenesis-related enzymes G6Pase and PEPCK in liver, kidney and intestine after fasting. (4 ) Glucagon upregulated p-PKA/PKA and p-CREB/CREB in liver. Conclusions Glucagon shows temporal difference in the gluconeo-genic response of liver, kidney and intestine in mice. Glucagon promotes the gene and protein expressions of key gluconeogenic enzymes G6Pase and PEPCK by increasing PGC-1α gene and protein expression, and thus increasing fasting blood glucose. Besides, glucagon promotes hepatic gluconeogenesis via PKA/CREB signaling pathway.