RESUMO
Advanced glycation end-products (AGEs) play a pivotal role in macro- and micro-vascular diabetic complications. We investigated the mechanism by which methylglyoxal (an endogenous generator of AGEs) affects vascular contractility using the isolated artery technique. Contractile responses to vasoconstrictors phenylephrine (PE), angiotensin II (Ang II), vasopressin (VP) and KCl were measured in the isolated rat aorta following one-our exposure to methylglyoxal (50-200⯵M). The perfused rat kidney was employed to confirm the effect of methylglyoxal on microvessels. Methylglyoxal-induced changes in cytosolic calcium were measured in the smooth muscle layer of the aorta with the calcium-sensing fluorophore Fluo-4 AM. Methylglyoxal significantly increased maximal contraction of the rat aorta to PE, Ang II and VP. Similar results were seen in response to the depolarizing vasoconstrictor KCl in macro and micro vessels. The methylglyoxal-induced increases in aortic contraction mediated by the agonist and KCl were endothelium independent. Methylglyoxal-induced increases in KCl-dependent aortic contraction were abolished after the removal of extracellular calcium or in the presence of the calcium channel blocker nifedipine. Incubation with the antioxidant N-acetyl-l-cysteine (NAC), apocynin (a nonselective NADPH oxidase (NOX) inhibitor) or chelerythrine (a protein kinase C (PKC) inhibitor) prior to methylglyoxal pre-treatment reversed the methylglyoxal-induced increases in the rat aortic contractility. In conclusion, the formation of AGEs increases vasoconstriction of both macro- and micro-vessels by increasing the voltage-activated calcium entry in vascular smooth muscles in a NOX and PKC dependent manner.
