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N. Wirtz, L. Wagenfeld, P. Galambos, A. Wiermann, N. Matthiesen, G. Richard, M. Klemm, O. Zeitz; Effects of Oxidative Stress on the Tone of the Posterior Ciliary Arteries in Porcine Eyes. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2292.
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Oxygen free radicals are known to increase vascular tone and may induce vasospasm. This might play a role in the pathogenesis of hemodynamic dysregulation that can be observed in primary open angle glaucoma. Aim of the present study was to investigate the effect of oxygen free radicals on the tone of pre-contracted posterior ciliary arteries and if pyruvate acts as a scavenger and has the capability to attenuate these vasospasms.Materials and
The experiments were carried out with fresh ring preparations from porcine ciliary arteries obtained from a slaughterhouse. The preparations were placed in a custom-designed myograph system and were kept under physiologic conditions (pH 7.4, 37Ãâ€~Ã‘Â°C, Krebs-Henseleit-Buffer, 1.8mM Ca2+). The muscles were half-maximally depolarised with -41mV Nernst potential for K+. All measured forces were normalized on the values of a full contraction provoked by K+-depolarization (Nernst-potential -4mV). The pre-activated preparations were exposed to hydroxyl radicals generated by the Fenton reaction (0.75mM H2O2; 10Ãâ€~Ã‘ÂµM Fe3+) for 10sec, 20sec, 1min and 2 min. Equal experiments were carried out in presence and absence of 1mM pyruvate.
Ten seconds radical exposure results in an additional increase of the relative developed force from 0.35Ãâ€~Ã‘Â±0.08 to 0.62Ãâ€~Ã‘Â±0.12 (P=0.003; n=8). Comparable results were obtained for 20 and 60s radical exposures. A two-minute exposure to hydroxyl radicals lead to an increase of vascular tone from 0.81Ãâ€~Ã‘Â±0.08 to 1.42Ãâ€~Ã‘Â±0.07 (P=0,003; n=15). In presence of pyruvate this increase was reduced from 0.78Ãâ€~Ã‘Â±0.03 to 1.12Ãâ€~Ã‘Â±0.03, which was a significant effect (P=0.003; n=14).
The data show that oxygen free radicals may induce transient contractions of isolated ciliary artery rings. The shape of these contractions displays parallels to vasospasms. Thus the established system may serve as an in vitro model of vasospasms. Pyruvate seems to be an effective scavenger at the ciliary vasculature.
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