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M. Hollingsworth, J.W. Kiel; Isoproterenol Increases Ciliary Blood Flow and Aqueous Production in Rabbits . Invest. Ophthalmol. Vis. Sci. 2006;47(13):214.
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To assess the effects of systemic infusion of a sub–pressor dose of isoproterenol (Iso) on ciliary blood flow and aqueous production.
This study used pentobarbital anesthetized rabbits (n=18, 2.25 ± 0.07 kg) in which the following variables were measured: mean arterial pressure (MAP), intraocular pressure (IOP), and orbital venous pressure (OVP) by direct cannulation, carotid blood flow by transit time ultrasound (BFcar, Transonic Systems TS420), heart rate (HR, digital cardiotachometer), ciliary blood flow by laser Doppler flowmetry (BFcil, Perimed PF 5000), and aqueous flow by fluorophotometry (Flow, Ocumetrics FM2). Measurements were made for 90 min before and during intravenous infusion of isoproterenol (0.055 µg/min/kg). Results are presented as mean ± SE for the last 60 min of each time period. Responses were evaluated by 2–tailed paired t–tests.
Iso is a non–selective beta adrenergic agonist with well known systemic effects such as the increased heart rate and vasodilation found in this study. The ocular effects of Iso are more complex, with several studies showing topical or intraocular Iso administration decreases IOP, but either increases or has no effect on aqueous production. In the present study, intravenous administration of a sub–pressor dose of Iso decreased IOP without changing OVP and stimulated aqueous production. Based on the control relationship between ciliary blood flow and aqueous production, the increased aqueous production is a direct response to Iso and not an indirect response to increased ciliary blood flow.
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