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Emer Henry, David E. Newby, David J. Webb, Patrick W. F. Hadoke, Colm J. O’Brien; Altered Endothelin-1 Vasoreactivity in Patients with Untreated Normal-Pressure Glaucoma. Invest. Ophthalmol. Vis. Sci. 2006;47(6):2528-2532. doi: 10.1167/iovs.05-0240.
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purpose. Vasospasm, resulting from a generalized dysfunction in the vascular endothelium, is implicated in the development of normal-pressure glaucoma (NPG). Impaired endothelium-derived nitric oxide activity and abnormalities of the endothelin system suggest systemic endothelial cell dysfunction in patients with NPG. Endothelin (ET)-1 vasoreactivity was assessed in the peripheral circulation of patients with NPG.
methods. Forearm blood flow was measured using venous occlusion plethysmography in eight patients with untreated NPG and eight age- and sex-matched healthy volunteers during intra-arterial infusion of ET-1 (5 pmol/min) and, on a separate occasion, to BQ123, a selective endothelin-A receptor antagonist, (100 nmol/min). Blood pressure and heart rate were measured in the noninfused arm, and plasma ET-1 concentrations were measured using a radioimmunoassay.
results. Forearm blood flow fell during infusion of ET-1 (P < 0.001 for both) to a similar extent in both groups (P = 0.7; patients versus control subjects). In contrast, BQ123 increased forearm blood flow in both groups (P < 0.001 for both), although the vasodilatation was lower in patients than in control subjects (P < 0.001; patients versus control subjects). There was no difference in basal plasma ET-1 concentrations between the two groups (P = 0.81; patients versus control subjects).
conclusions. Despite normal responses to ET-1, patients with NPG have reduced vasodilatation in response to ETA-receptor antagonism. This could be due to attenuated ETA-receptor–mediated tone, increased ETB-receptor–mediated contraction or impaired ETB-receptor-mediated release of endothelial nitric oxide. These results are consistent with the authors’ previous demonstration of systemic vascular dysfunction in patients with NPG.
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