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M. S. Torring, C. Aalkjaer, T. Bek, Department of Ophthalmology, Aarhus University Hospital; U46619 and High Potassium Induce a Similar Diameter Response on Each Side of Bifurcations of Porcine Retinal Arterioles in vitro. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5003.
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Retinal blood flow is mainly regulated by the tone of retinal arterioles, but the relative contribution of smaller and larger arterioles to the formation of tone is unknown. Evidence suggests that arteriolar bifurcations may play a central role for the generation of tone waves that propagate along arterioles. Consequently, it is possible that the tone response to pharmacological stimuli before and after these structures may be different.
12 retinal arteriolar bifurcations from 9 porcine eyes were studied. After removal of the retina the upper half including a larger arteriole and venule was mounted in a specially designed tissue chamber. The larger retinal vessels supplying the segment were cannulated, and the preparation was placed in an inverted microscope with a mounted video camera, which was adjusted so that an arterial bifurcation was in the field of view. The vascular diameter was measured down- and upstream the bifurcation, before and after addition of either the tromboxane analogue U46619 (10-6M) or PSS with high (125mM) potassium that are known to effect vascular tone through different mechanisms.
At rest the total cross sectional area of the two daughter vessels was 122,3 % ± 5,6 % of the area of the unbranched vessel before the bifurcation (n=12).U46619 reduced the cross sectional area of the parent arteriole with 36,5 % ± 16,2 % (n=9) and the sum of the cross sectional area of the daughter arterioles similarly with 40,7 % ± 13,9 % (n=18). The corresponding reductions of the cross sectional area induced by high potassium was significantly higher (p<0,001), i.e. 70,9 % ± 8,9 % (n=9) and 77,8 % ± 8,4 %, respectively (n=18).
The cross sectional area of the daughter arterioles was larger than that of the parent arteriole, which may compensate for an increase in the resistance.There was no significant difference between the changes induced by U46619 and potassium in the cross sectional area of retinal arterioles before and after bifurcations. This argues against the arterial bifurcations as dividing points between vascular segments with different tone regulation.
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