Abstract
The study has been designed to investigate the effect of 8-Br-cAMP, an activator of protein kinase A (PKA), in diabetes mellitus– and hyperhomocysteinemia-induced vascular endothelial dysfunction. Streptozotocin (55 mg kg−1, i.v.) and methionine (1.7% w/w, p.o., 4 weeks) were administered to rats to produce diabetes mellitus (serum glucose >200 mg dL−1) and hyperhomocysteinemia (serum homocysteine >10 μM), respectively. Vascular endothelial dysfunction was assessed using isolated aortic ring preparation, electron microscopy of thoracic aorta, and serum concentration of nitrite/nitrate. The expression of mRNA for p22phox and endothelial nitric oxide synthase (eNOS) was assessed by using reverse transcriptase–polymerase chain reaction (TBARS) (RT-PCR). Serum thiobarbituric acid–reactive substances (TBARS) concentration and aortic superoxide anion concentration were estimated to assess oxidative stress. 8-Br-cAMP (5 mg kg−1, i.p.) or atorvastatin (30 mg kg−1, p.o.) prevented diabetes mellitus– and hyperhomocysteinemia-induced attenuation of acetylcholine-induced endothelium-dependent relaxation, impairment of vascular endothelial lining, decrease in expression of mRNA for eNOS, serum nitrite/nitrate concentration, and increase in expression of mRNA for p22phox, superoxide anion, and serum TBARS. The ameliorative effect of 8-Br-cAMP was prevented by Nω-nitro-L-arginine methyl ester (L-NAME) (25 mg kg−1, i.p.) and glibenclamide (5 mg kg−1, i.p.). Therefore, it may be concluded that 8-Br-cAMP–induced activation of PKA may improve vascular endothelial dysfunction.
Notes
1Abbreviations: Acetylcholine (ACh); endothelial nitric oxide synthase (eNOS); glyseraldehyde-3-phosphate dehydrogenase (GAPDH); reverse transcriptase–polymerase chain reaction (RT-PCR); N(ω)-nitro-L-arginine methyl ester (L-NAME); nitroblutetrazolium (NBT); protein kinase A (PKA); sodium nitroprusside (SNP); thiobarbituric acid–reactive substances (TBARS).