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Barbara Bogner, Christian Runge, Clemens Strohmaier, Andrea Trost, Falk Schroedl, Herbert A. Reitsamer; Effects of Low- and High-dose Application of Vasopressin on Aqueous Humor Dynamics. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1981.
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Previous experiments have shown that vasopressin reduces IOP dose-dependently. The purpose of the present study is to investigate the effect of different doses of arginine-vasopressin (AVP) on aqueous flow (AF).Ciliary blood flow (CilBF) and aqueous production are related to each other. To distinguish between blood flow and secretory mediated effects of AVP on AF, two doses of exogenously applied AVP were selected: The first dose did not change CilBF (defined as low-dose); the second dose caused a significant reduction of CilBF (defined as high-dose).
In anesthetized New Zealand white rabbits mean arterial pressure (MAP), intraocular pressure (IOP) and orbital venous pressure (OVP) were measured continuously by direct cannulation of the central ear artery, the vitreous and the orbital venous sinus, respectively. CilBF was measured transsclerally by laser-Doppler flowmetry. Aqueous flow (AF) was determined simultaneously by fluorophotometry. After baseline measurements the effects of exogenously applied AVP (0.08 ng/kg/min and 1.33 ng/kg/min) were recorded.
At the selected low-dose of AVP CilBF was not changed, the high-dose of AVP caused a significant reduction of CilBF (-35.68±4.00%). Low-dose and high-dose AVP reduced the AF ~20%. Detailed results are summarized in table 1.
Both low- and high-dose AVP cause ~20% reduction of AF. It has been shown, that CilBF reduction of more than ~25% of its normal level results in a proportional decrease of aqueous production. The model of the relationship between CilBF and AF suggests that low-dose AVP modulates aqueous production due to the inhibition of secretory mechanisms in the ciliary epithelium, as CilBF is not changed. High-dose AVP additionally causes a reduction in CilBF and vasoconstriction. One would expect that there is a proportional decrease in AF. However, AF is not further reduced. Therefore, additional factors (e. g. stimulatory mechanisms or starling forces) might play a role. However, to clarify this was beyond the scope of this study.
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