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Barbara Bogner, Christian Runge, Andrea Trost, Falk Schrödl, Alexandra Kaser-Eichberger, Daniela Bruckner, Clemens Strohmaier, Herbert A Reitsamer; Oxytocin-induced Effects on Intraocular Pressure and Ocular Blood Flow. Invest. Ophthalmol. Vis. Sci. 2018;59(9):3201. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Oxytocin (OT) and arginine-vasopressin (AVP) are hormones and neuropeptides with closely related structures differing only at position 3 and 8 of their amino acid sequence. While isoleucine at position 3 is crucial for OT receptor stimulation, AVP receptor activation is mediated via arginine at position 8. It is known that AVP can modulate ocular parameters; however, the effect of OT has not been investigated. The aim of the present study is to examine the effect of OT on intraocular pressure (IOP) as well as on choroidal and ciliary blood flow (ChorBF, CilBF).
In anesthetized New Zealand rabbits (n = 5) mean arterial pressure (MAP), IOP and orbital venous pressure (OVP) were measured by direct cannulation of the central ear artery, the vitreous and the orbital venous sinus, respectively. Laser Doppler flowmetry was used to record ChorBF and CilBF. To change the perfusion pressure (PP) over a wide range, MAP was manipulated mechanically via occluders placed around the aorta and the inferior vena cava. After baseline measurements, OT was intravenously infused (2.50 µg/kg/min) and changes compared to baseline and pressure-flow relationships were analysed.
Compared to baseline conditions, the applied dose of OT reduced ChorBF by 43.77±12.30 % (p < 0.05) and CilBF by 64.19 ± 8.75 % (p < 0.05). PP increased by 23.60 ± 7.87 (p < 0.05) and the pressure-flow relationship in both vascular beds revealed a significant downward shift (p < 0.05). In addition, IOP (-40.92 ± 4.01 %, p < 0.05) and OVP (-135.23 ± 12.47% p < 0.001) declined. The MAP tended to increase (9.35 ± 7.24%), but reached no statistical significance.
OT-application at a relatively high concentration has a pronounced hypotensive effect on IOP in rabbits. In addition, it causes vasoconstriction in the choroid and in the ciliary body. In previous studies, similar effects have been measured for significantly lower doses of AVP (differing by the factor 10^3), indicating a higher threshold for efficacy of OT in ocular tissues. In addition, for both, AVP and OT, a dose-dependent tissue response is described. To differentiate between hypotensive and vasoactive effects of OT in ocular tissues and to exclude receptor cross-reactivity, refinement of the dose-response by down titration of the OT is planned in future studies.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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