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J W Kiel, M O Lovell; Adrenergic modulation of choroidal blood flow in the rabbit.. Invest. Ophthalmol. Vis. Sci. 1996;37(4):673-679.
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PURPOSE: To determine whether the choroidal pressure-flow is altered by the alpha-adrenergic antagonist, phentolamine, or the beta-adrenergic antagonist, propranolol. METHODS: In two groups of pentobarbital- anesthetized rabbits, the choroidal pressure-flow relationships were determined by raising the intraocular pressure (IOP) at mean arterial pressure (MAP) of 50, 60, 70, and 80 mm Hg before and after phentolamine (0.5 mg/kg, intravenously, n=7) and propranolol (0.25 mg/kg intravenously, n=7) administration. Hydraulic occluders on the thoracic aorta and inferior vena cava were used to control MAP, which was measured in the central ear artery. The eye was cannulated with two 23-gauge needles, one to manipulate the ocular volume and the other to measure the IOP. Choroidal blood flow was measured by laser Doppler flowmetry with a probe positioned over the posterior retina. The protocol consisted of setting the MAP, then infusing saline into the eye at 30 microliters/minute until the IOP increased from baseline to 100 mm Hg. RESULTS: At the MAP of 70 mm Hg, alpha-adrenergic blockade caused an upward shift in the choroidal pressure-flow relationship; beta-blockade shifted the relationship downward. CONCLUSIONS: In the pentobarbital-anesthetized rabbit, alpha- and beta- adrenergic blockade cause choroidal vasodilation and vasoconstriction, respectively. Results indicate the presence of alpha- and beta-adrenergic receptors in the rabbit choroid and a tonic level of adrenergic vascular tone in this preparation.
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