Endothelial Endothelin B Receptor-Mediated Prevention of Cerebrovascular Remodeling Is Attenuated in Diabetes Because of Up-Regulation of Smooth Muscle Endothelin Receptors

Structure and function of the cerebrovasculature is critical for ischemic stroke outcome. We showed that diabetes causes cerebrovascular remodeling by activation of the endothelin A (ETA) receptors. The goal of this study was to test the hypotheses that vasculoprotective endothelial ETB receptors are decreased and pharmacological inhibition of the ETB receptor augments vascular remodeling of middle cerebral arteries (MCAs) in type 2 diabetes. MCA structure, matrix metalloprotease (MMP) activity, and matrix proteins as well as ETA and ETB receptor profiles were assessed in control Wistar and diabetic Goto-Kakizaki rats treated with vehicle, the ETB receptor antagonist (2R, 3R, 4S)-4-(1,3-benzodioxol-5-yl)-1-[2-[(2,6-diethylphenyl) amino]-2-oxoethyl]-2-(4-propoxyphenyl)pyrrolidine-3-carboxylic acid (A192621) (30 mg/kg/day), or the dual ET receptor antagonist bosentan (100 mg/kg/day) for 4 weeks. Diabetes increased vascular smooth muscle (VSM) ETA and ETB receptors; the increase was prevented by chronic bosentan treatment. MCA wall thickness was increased in diabetes, and this was associated with increased MMP-2 activity and collagen deposition but reduced MMP-13 activity. Because of up-regulation of VSM ET receptors in diabetes, selective ETB receptor antagonism with A192621 blunts this response, and combined ETA and ETB receptor blockade with bosentan completely prevents this response. On the other hand, A192621 treatment augmented remodeling in control animals, indicating a physiological protective role for this receptor subtype. Attenuation of changes in ET receptor profile with bosentan treatment suggests that ET-1 has a positive feedback on the expression of its receptors in the cerebrovasculature. These results emphasize that ET receptor antagonism may yield different results in healthy and diseased states.