Role of the endothelium in modulating functional responses of isolated bovine anterior ciliary arteries to vasoconstrictor agonists.
(65/68)
BACKGROUND/AIMS: Endothelium dependent vasodilatation is an important regulator of blood flow to the eye but its role has not been investigated in vessels supplying the ciliary body. This study assessed the role of the endothelium in modulating vasoconstrictor responses of the intraocular bovine anterior ciliary artery. METHODS: Bovine anterior ciliary arteries (n = 33) were mounted in a myograph, containing physiological salt solution at 37 degrees C, for isometric force measurement. Cumulative concentration-response curves were obtained to the constrictor agonists 5-hydroxytryptamine (5-HT), noradrenaline, phenylephrine, prostaglandin, F2 alpha, endothelin-1, and KCl in both endothelium intact and denuded arteries. RESULTS: All vasoconstrictors produced sustained contractile responses which were unaffected by the removal of the endothelium. Responses to 5-HT were also unaffected by inhibition of nitric oxide synthase. CONCLUSION: These results indicate that neither agonist stimulated nor basal release of nitric oxide from the endothelium modulates responses to vasoconstrictor agonists in the isolated bovine anterior ciliary artery when measured in a no flow isometric system. (+info)
Zinn-Haller arterial ring observed by ICG angiography in high myopia.
(66/68)
AIMS: To delineate the entire Zinn-Haller arterial ring angiographically in vivo. METHODS: 382 highly myopic eyes (210 patients) with refractive errors greater than -8.25 D were examined using indocyanine green (ICG) videoangiography. A control group of 80 eyes (40 patients) had refractive errors within plano +/- 3D. RESULTS: The Zinn-Haller ring was visible in 206 of 382 highly myopic eyes (53.9%) by ICG angiography. Although only a part of the Zinn-Haller ring was visible in 162 of 206 eyes, in the remaining 44 eyes it was observed almost completely around the optic nerve head. No anastomotic channels between lateral and medial short posterior ciliary arteries were filled by ICG angiography. In 22 of the 44 eyes (50.0%) the Zinn-Haller ring was supplied by branches of the lateral and medial short posterior ciliary arteries; in seven eyes, it was supplied only by the lateral short posterior ciliary artery; and in seven eyes, it was supplied only by the medial short posterior ciliary artery. In none of the control subjects was the Zinn-Haller ring visible by ICG angiography. CONCLUSIONS: The Zinn-Haller ring observed by ICG angiography was not a complete collateral circle between lateral and medial posterior ciliary arteries. Also, the patterns in supply vessels to the Zinn-Haller ring varied. ICG angiography made possible the detailed observation of the Zinn-Haller ring in human eyes in vivo. (+info)
Effects of topical beta-blockers on the diameter of the isolated porcine short posterior ciliary artery.
(67/68)
PURPOSE: Based on diameter measurements on the short posterior ciliary artery, this study was intended to determine the direct pharmacologic effect of beta-blockers; to determine the differences among a selective beta-blocker betaxolol, a beta-blocker with intrinsic sympathetic activity befunolol, and a nonselective beta-blocker timolol; and to find experimental evidence for the indirect hemodynamic effect of beta-blockers. METHODS: A segment of isolated porcine short posterior ciliary artery was cannulated at both ends and mounted in a pressurized vessel chamber. Vessel diameter was measured as a function of beta-blocker concentration and as a function of change in transmural pressure. RESULTS: In the absence of flow, the mean effective doses (ED50) were 0.8 +/- 0.3 mM, 1.0 +/- 0.3 mM, and 11.6 +/- 6.6 mM (SEM) for betaxolol, befunolol, and timolol, respectively. In the presence of flow, vessel diameter increased with an increase of transmural pressure. The mean relative diameter increased 4.2% +/- 1.0% (SEM) at a transmural pressure step from 30 mm Hg to 60 mm Hg. This increase was not significantly dependent on the presence of any of the beta-blockers. CONCLUSIONS: Only at concentrations far exceeding their expected plasma concentrations, betaxolol, befunolol, and timolol increased the diameter of the isolated porcine short posterior ciliary artery, as a result of their direct pharmacologic effect. Only the difference between the vasodilatory potency of the selective and the nonselective beta-blocker was significant: ED50 of betaxolol was 15 times smaller than ED50 of timolol. There was a positive correlation between the diameter of the isolated porcine short posterior artery (when used as a model for an intraocular artery) and the transmural pressure, which corroborates the indirect hemodynamic effect of beta-blockers. It is speculated that instillation of topical beta-blockers into the conjunctival sac may increase the perfusion of the optic nerve head by an indirect hemodynamic mechanism, but not by a direct pharmacologic mechanism. (+info)
Wall cytoarchitecture of the rat ciliary process microvasculature revealed with scanning electron microscopy.
(68/68)
Ciliary process vasculature has an important role in aqueous humor production. There have been, however, few reports describing the overall cytoarchitecture of ciliary process vasculature. The wall cytoarchitecture of microvessels in the rat ciliary process was elucidated by scanning electron microscopy after removal of ciliary epithelia and connective tissue components with HCl hydrolysis. Utilizing characteristics of cellular morphology and vessel diameters, several vascular components were identified along the vascular tree: 1) arterial iridociliary circles (30-60 microm in outer diameter), containing a compact layer of circularly oriented spindle-shaped smooth muscle cells; 2) the proximal part of the radial ciliary arteriole (10-25 microm), containing a less compact layer of circularly oriented branched-smooth muscle cells and spindle-shaped smooth muscle cells; 3) a middle part of the radial ciliary arteriole (20-35 pm), with circularly oriented branched-smooth muscle cells and irregularly oriented stellate cells with ramifying projections; 4) a distal part of the radial ciliary arteriole (10-20 microm), possessing irregularly oriented stellate cells with ramifying projections; 5) marginal venules (15-20 microm), with spidery pericytes possessing highly ramifying and overlapped projections; 6) capillaries in the ciliary process (4-7 microm), with widely scattered pericytes having longitudinal and several circular projections; 7) venules in the posterior basal region of the ciliary process (greater than 5 microm), with widely scattered pericytes having a few thin projections. From arterial iridociliary circles to venules in the basal region of ciliary process, seven parts could be recognized by wall cytoarchitecture, which was discussed in relation with the function. (+info)