Endothelial dysfunction and metabolic control in streptozotocin‐induced diabetic rats

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Abstract
1 The aim of this work was to study the influence of the metabolic control, estimated by the levels of glycosylated haemoglobin in total blood samples (HbA(1c)), in developing vascular endothelial dysfunction in streptozotocin-induced diabetic rats. Four groups of animals with different levels of insulin treatment were established, by determining HbA(1c) values in 5.5 to 7.4%, 7.5 to 9.4%, 9.5 to 12% and >12%, respectively. 2 The parameters analysed were: (1) the endothelium-dependent relaxations to acetylcholine (ACh) in isolated aorta and mesenteric microvessels; (2) the vasodilator responses to exogenous nitric oxide (NO) in aorta; and (3) the existence of oxidative stress by studying the influence of the free radical scavenger superoxide dismutase (SOD) on the vasodilator responses to both ACh and NO. 3 In both isolated aortic segments and mesenteric microvessels, the endothelium-mediated concentration-dependent relaxant responses elicited by ACh were significantly decreased when the vessels were obtained from diabetic animals but only with HbA(1c) values higher than 7.5%. There was a high correlation between HbA(1c) levels and the impairment of ACh-induced relaxations, measured by pD(2) values. 4 The concentration-dependent vasorelaxant responses to NO in endothelium-denuded aortic segments were significantly reduced only in vessels from diabetic animals with HbA(1c) values higher than 7.5%. Again, a very high correlation was found between the HbA(1c) values and pD(2) for NO-evoked responses. 5 In the presence of SOD, the responses to ACh or NO were only increased in the segments from diabetic rats with HbA(1c) levels higher than 7.5%, but not in those from non-diabetic or diabetic rats with a good metabolic control (HbA(1c) levels <7.5%). 6 These results suggest the existence of: (1) a close relation between the degree of endothelial dysfunction and the metabolic control of diabetes, estimated by the levels of HbA(1c); and (2) an increased production of superoxide anions in the vascular wall of the diabetic rats, which is also related to the metabolic control of the disease.