High glucose effects on endothelium-dependent vasorelaxation in isolated thoracic aorta of spontaneously hypertensive rats

Abstract

There is an increasing evidence regarding the relationship between metabolic syndrome components and cardiovascular complications leading to vascular disorders and type 2 diabetes. Cardio-metabolic risk factors have been reported to promote the development of endothelial dysfunction. Nevertheless, the direct impact of these factors on the mechanisms underlying endothelial dysfunction remain poorly understood. The aim was to identify the impact of hyperglycaemia on endothelial function in spontaneously hypertensive rat (SHR). For this we investigated the direct effect of high glucose short-term incubation on endothelium-dependent relaxation on isolated thoracic aorta. Thirty-eight SHR males, 12-weeks old (weighting on average 330 g) were used for this study. Thoracic aortae were isolated and cut into rings. Aortic rings were precontracted with 1 μM phenylephrine and cumulative concentration-response curves (CCRCs) to acetylcholine (1 nM to 0.1 mM) and sodium nitroprusside (10 nM to 10 μM) were performed in aortic rings exposed during two hours to a normal (11 mM) or to a high glucose concentration (25 mM). A non-linear mixed effects model was used to compare the CCRCs parameters (pD2 and Emax). A significant level of P = 0.05 was used for statistical comparison. In phenylephrine-precontracted rings, acetylcholine produced a concentration-dependent relaxation (Emax = 87.06 ± 3.04% and pD2 was 6.99 ± 0.06; n = 20). Incubation of aortic rings in high glucose for 2 hours led to an impairment of the acetylcholine-induced relaxation (pD2 = 6.57 ± 0.08 and Emax = 79.95 ± 4.19%; P < 0.001 vs. control; n = 20). Pretreatment of aortic rings with apocynin (30 μM), a NADPH oxidase inhibitor, or indomethacin (1 μM), a non-selective COX inhibitor, increased the maximal effect of acetylcholine-induced relaxation (Emax = 101.06 ± 5.20% and Emax = 97,98 ± 4.70% after apocynin and indomethacin respectively, P < 0.01 vs. control) in control group. The vasorelaxation was also improved in the high glucose group (Emax = 97.96 ± 4.70% and 102.34 ± 5.05% respectively, P < 0.001 vs. high glucose group after apocynin or indomethacin respectively), with an increase of acetylcholine sensitivity by indomethacin (pD2 = 7.23 ± 0.10; P < 0.001 vs. high glucose group after indomethacin). We found that short-term incubation with high glucose led to an impairment of endothelium-dependent relaxation of SHR thoracic aorta. This impairment could involve NADPH oxidase and COX products, that may be responsible for a decrease of nitric oxide bioavailability and its vasorelaxant activity.