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B. Bogner, B. Tockner, C. W. Runge, C. Strohmaier, G. Grabner, H. A. Reitsamer; The Effect of Vasopressin on Ocular Hemodynamics and Aqueous Flow. Invest. Ophthalmol. Vis. Sci. 2008;49(13):359.
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To investigate the dose-dependent effects of vasopressin (AVP) on ciliary blood flow (CilBF) and choroidal blood flow (ChorBF) and its influence on aqueous flow (AF).
In anesthetized rabbits mean arterial pressure (MAP), intraocular pressure (IOP) and orbital venous pressure (OVP) were measured by direct cannulation of the central ear artery, the vitreous, and the orbital venous sinus, respectively. To change the perfusion pressure (PP) over a wide range, MAP was manipulated mechanically via occluders placed around the aorta and the vena cava. Laser Doppler flowmetry was employed for continuous recording of CilBF and ChorBF. AF measurement was performed simultaneously by flourophotometry. For evaluating the dose-response (n = 11) AVP was administered intravenously at different application rates (ng/kg/min) after baseline measurements. Pressure-flow (PF) relationships (n = 5) were measured at control and in response to AVP (0.08 ng/kg/min and 1.33 ng/kg/min). The selected dose for fluorophotometry (n = 9) was 0.08 ng/kg/min.
AVP caused a dose-dependent increase of MAP, ciliary and choroidal vascular resistance (ChorR, CilR), while IOP, OVP, CilBF, ChorBF and HR were decreased. The PF relationship revealed a significant vasoconstriction in the choroidea at both low-dose and high-dose AVP, whereas in the ciliary body the distinct vasoconstrictive effect was solely detected at high-dose application. The data obtained from fluorophotometry indicated a significant decrease of AF after low-dose AVP application, although CilBF was not lowered considerably.
Apart from substantiating the pronounced vasoconstrictive effects of AVP we could show that the choroidal vascular bed is more sensitive to AVP than the ciliary vascular bed. While in the choroid AVP causes vasoconstriction over a wide range of PP at both low-dose and high-dose, in the ciliary body the vasoconstrictive effect is restricted to high-dose application. Furthermore, we conclude that the reduction of AF after low-dose AVP is induced predominantly by affecting the secretory mechanisms but not by a reduction of ciliary blood flow.
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