br Materials and methods br Results br Discussion The main

Materials and methods
Results
Discussion The main finding of the present study is that selective ETA and dual ETA/ETB receptor blockade markedly improve endothelium-dependent vasodilatation in patients with type 2 diabetes and vascular complications. The magnitude of improvement did not differ between the two treatment strategies. The results suggest that addition of ETB blockade to ETA blockade does not provide additional beneficial effects on endothelial function in this patient group. Previous studies have demonstrated that ET-1 is of importance for the development of endothelial dysfunction. ET receptor blockade does not affect endothelium-dependent vasodilatation in healthy subjects (Shemyakin et al., 2006). In subjects with insulin-resistance but without cardiovascular disease, it was shown that dual ETA/ETB blockade but not selective ETA blockade improved endothelial function (Shemyakin et al., 2006). This observation was supported by the finding that the dual antagonist bosentan improved peripheral endothelial function in patients with type 2 diabetes and microvascular complications (Rafnsson et al., 2012). On the other hand, a recent study demonstrated that 6months treatment with the oral ETA receptor antagonist atrasentan improved coronary endothelial function in patients with atherosclerosis (Reriani et al., 2010). The current study is to the best of our knowledge the first to directly compare the effect of selective ETA with dual ETA/ETB receptor blockade on patients with developed cardiovascular diseases. There was no difference between the two different treatment strategies meaning that both selective ETA and dual ETA/ETB inhibition were equally effective in improving endothelium-dependent vasodilatation in patients with type 2 diabetes and coronary artery disease. The observation is important due to the concern that blockade of ETB receptors on endothelial inhibitor of apoptosis proteins may impair release of nitric oxide and thereby endothelium-dependent vasodilatation. Such an effect does not seem to be of functional relevance in the present patient group which has markedly impaired bioavailability of NO (Shemyakin et al., 2012). Efficient blockade of the ETB receptor (clearance receptor) was confirmed by the finding that plasma ET-1 levels increased only following dual ETA/ETB receptor blockade. Collectively our data show that dual ETA/ETB receptor blockade seems to improve endothelial function as efficiently as selective ETA blockade. In addition to improving endothelium-dependent vasodilatation, dual ETA/ETB blockade significantly increased baseline forearm blood flow, whereas selective ETA blockade did not. This observation is in line with the previous demonstration that vascular smooth muscle cell expression of ETB receptors is upregulated in atherosclerosis and in type two diabetes (Pernow et al., 2012, Iwasa et al., 1999, Li et al., 2011). Such upregulation may explain an increase in vascular tone mediated by the ETB receptor. The clinical significance of a reduced vascular tone mediated by dual receptor blockade is unknown but theoretically it might have a long term effect by reducing arterial stiffness and thus reducing secondary vascular complications of diabetes. Furthermore, dual ET receptor blockade has been demonstrated to increase insulin sensitivity in patients with insulin resistance (Shemyakin et al., 2010). Both selective and dual receptor blockade also increased endothelium-independent vasodilatation induced by SNP. Previous studies using ET receptor blockade and other interventions aiming at increasing nitric oxide bioavailability have demonstrated that not only endothelium-dependent but also endothelium-independent vasodilatation was increased in patients with type 2 diabetes but not in patients without diabetes (Shemyakin et al., 2006, Shemyakin et al., 2012, Shemyakin et al., 2011). These observations suggest an effect on vascular smooth muscle cells or increased bioavailability also of exogenously administered NO among this patient group.