Effect of Glucagon-Like Peptide-1(7–36) and Exendin-4 on the Vascular Reactivity in Streptozotocin/Nicotinamide-Induced Diabetic Rats

Abstract

We investigated the vascular effects of glucagon-like peptide-1 (GLP-1) and Exendin-4 in type 2 diabetic rat aortae. Studies were performed in a normal control group (NC) (0.2 ml i.p. saline, n = 10), streptozotocin (STZ)/nicotinamide diabetic control group (DC) (a single dose of 80 mg/kg STZ i.p. injection 15 min after administration of 230 mg/kg nicotinamide i.p.), GLP-1 (GLPC) control group (1 µg/kg twice daily i.p. for 1 month, n = 10), Exendin-4 control group (EXC) (0.1 µg/kg twice daily i.p. for 1 month, n = 10), GLP-1-treated diabetic group (GLPT) (1 µg/kg twice daily i.p. for 1 month, n = 10), and Exendin-4-treated diabetic group (EXT) (0.1 µg/kg twice daily i.p. for 1 month, n = 10). One month of GLP-1 and Exendin-4 treatment significantly decreased the blood glucose levels of diabetic rats (113 ± 2 mg/dl, p < 0.001, and 117 ± 1 mg/dl, p < 0.001, respectively versus 181 ± 9 mg/dl in the DC group). Sensitivity (pD₂) and maximum response (% Max. Relax) of acetylcholine-stimulated relaxations in the DC group (pD₂: 6.73 ± 0.12 and 55 ± 6, respectively) were decreased compared with the non-diabetic NC group (pD₂: 7.41 ± 0.25, p < 0.05, and 87 ± 4, p < 0.01). Treating diabetic rats with GLP-1, pD₂ values and with Exendin-4, Max. Relax %values of aortic strips to acetylcholine returned to near non-diabetic NC values (pD₂: 7.47 ± 0.15, p < 0.05, and 87 ± 3, p < 0.01, respectively). Maximal contractile responses (E_max) to noradrenaline in aortic strips from the diabetic DC group (341 ± 27 mg tension/mg wet weight) were significantly decreased compared with the non-diabetic NC (540 ± 66 mg tension/mg wet weight, p < 0.001) and the GLPT group (490 ± 25 mg tension/mg wet weight, p < 0.05). There were no significant differences in pD₂ values of aortic strips to noradrenaline from all groups. E_max to KCl in aortic strips from the DC group (247 ± 10 mg tension/mg wet weight, p < 0.01) was significantly decreased compared with non-diabetic NC group (327 ± 26 mg tension/mg wet weight). Treating diabetic rats with GLP-1 (GLPT), E_maxvalues of aortic strips to KCl returned to near non-diabetic NC values (271 ± 12 mg tension/mg wet weight). GLP-1 and (partially) Exendin-4 treatment could improve the increased blood glucose level and normalize the altered vascular tone in type 2 diabetic rats.