The aim of the present study was to examine the effect of an early stage of streptozotocin-induced diabetes on the mechanism(s) of endothelium-dependent relaxation. Diabetes was induced by a single injection of streptozotocin (48 mg/kg, i.v) and the ACh-induced relaxation of rat carotid arteries was examined 6 weeks later. A diabetes-induced increase in superoxide levels, determined by L-012-induced chemiluminescence, from carotid arteries was associated with endothelial NOS (eNOS) uncoupling and increased Nox2 expression. The sensitivity and maximum response to ACh was similar in normal and diabetic rats despite a decrease in NO release by DAF-FM. In normal rats, N-nitro-L-arginine (100 μM) plus ODQ (10 μM), to inhibit nitric oxide synthase (NOS) and soluble guanylate cyclase (sGC) respectively, abolished ACh-induced relaxation whereas in diabetic rats, the maximum relaxation to ACh was attenuated (Rmax 25±5%), but not abolished, by that treatment. The remaining ACh-induced relaxation was abolished by nitric oxide scavengers, cupric chloride (to degrade nitrosothiols) or blockers of endothelial potassium channels. Western blot analysis of the carotid arteries indicated that diabetes significantly increased the expression of eNOS, but decreased the proportion of eNOS expressed as the dimer. These findings demonstrate that in early diabetes ACh-induced relaxation is maintained but is resistant to NOS inhibition. In early diabetes, nitrosothiol-mediated opening of potassium channels may act in conjunction with NO stimulation of sGC to maintain endothelium-dependent relaxation despite the increase in vascular superoxide levels.
- endothelial nitric oxide synthase
- nitric oxide
- soluble guanylate cyclase
- Copyright © 2009, American Journal of Physiology - Heart and Circulatory Physiology