Our findings provide strong evidence that there is a delicate balance of vascular and endothelial ET receptors. When this balance is optimal, blockade of ETB receptors either directly via inhibition of ETB receptor activation LDP-341 or indirectly through the activation of ETA receptors leads to remodeling. Because recent studies suggest a rather complex and antihypertensive effects of ETB receptors, it is also possible that elevated blood pressure with A192621 may contribute to cerebrovascular remodeling in control animals (Pollock, 2010). However, the fact that both treatments prevent remodeling in diabetic animals despite similar increases in blood pressure argues against this possibility. These results point to a contrasting effect of ETB blockade in control and diabetic animals.

Although concomitant ETA blockade does not add or subtract from effects mediated by selective ETB blockade in controls, additional ETA blockade improves beneficial effects of ETB antagonism in diabetes. When the vascular/endothelial ET receptor balance is compromised as we found in the diabetic animals in the current study, vascular ETA and ETB receptors override protection conferred by the endothelial ETB receptors and therefore dual ETA/ETB receptor blockade completely restored indices of remodeling to control values. There are several technical limitations of the current study. First, because of the limited availability of the selective ETB antagonist A192621 we had a relatively small number of animals in the control group, and the receptor density studies were performed only in the bosentan treatment group.

Second, we measured ET receptor densities by immunoblotting because receptor binding studies require significantly more MCA samples and additional animals treated with these antagonists are needed. Along the same lines, eETB receptor density was determined by an indirect method. Although antibodies yielded specific bands in immunoblots, immunohistochemical studies to determine endothelial versus VSM ETB receptors were not clear (data not shown). We have also observed a 10 to 15% weight loss in both control and diabetic animals treated with antagonists. Our finding that treated control animals show increased remodeling despite weight loss argues against the fact weight loss may be contributing to the beneficial effects observed in diabetic animals.

However, the cause of weight loss and effect on remodeling endpoints need to be studied further. Despite these shortcomings, our results have demonstrated that selective ETB receptor antagonism exerts different effects Dacomitinib under physiological or diabetic conditions and dual ET receptor blockade completely prevents cerebrovascular remodeling in diabetes. These findings emphasize that the relative ETA and ETB receptor density is an important determinant of response to ET receptor antagonist treatment especially in disease states.