Fig. 5

Liraglutide stimulated NO production via the cAMP/PKA/AMPK/eNOS pathway in HUVECs. NO production by HUVECs was determined by measuring levels of the stable metabolites of NO (NO₂ and NO₃) in the culture medium. HUVECs were stimulated with the indicated concentrations of agents (saline or liraglutide 0.1–100 nmol/L) for 2 h, following serum starvation in M199, 0.3% FBS, for 1 h. Inhibitors were added 30 min prior to stimulation at the following concentrations: GLP-1R antagonist exendin-(9–39) (Ex-9), 100 nmol/L; cAMP inhibitor SQ22536 (SQ), 100 μmol/L; cAMP-dependent protein kinase (PKA) inhibitor fragment 14–22 myristoylated trifluoroacetate salt (PKI[14–22]), 1 μmol/L; exchange factor directly activated by cAMP inhibitor (ESI-09), 6.4 μmol/L; calcium-calmodulin-dependent protein kinase kinase inhibitor (STO-609), 10 μmol/L; AMP-activated protein kinase (AMPK) inhibitor (dorsomorphine), 10 μmol/L; Akt inhibitor 10-(4′-[[N-diethylamino]]butyl)-2-chlorophenoxazine (AktI X), 5 μmol/L; NOS inhibitor (l-NAME), 1 mmol/L; a effects of liraglutide and the Ex-9 GLP-1R antagonist on endothelial NO production, 2 h after stimulation; b effects of inhibitors of downstream molecules of GLP-1R on liraglutide-stimulated NO production; n = 4–6; *p < 0.05, ** < 0.01 vs. vehicle; ^†p < 0.05 vs. liraglutide 1 nmol/L