Adrenergic modulation of choroidal blood flow in the rabbit.
OBJECTIVE
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.
Kiel
J W
JW
Department of Ophthalmology, University of Texas Health Science Center, San Antonio, 78284, USA.
Lovell
M O
MO
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure; D002829:Choroid / Q000098:blood supply* / Q000187:drug effects; D005260:Female; D007429:Intraocular Pressure; D017078:Laser-Doppler Flowmetry; D008297:Male; D010646:Phentolamine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D012039:Regional Blood Flow / Q000187:drug effects; D013564:Sympathetic Nervous System / Q000502:physiology; D014661:Vasoconstriction; D014664:Vasodilation
D000317:Adrenergic alpha-Antagonists; D000319:Adrenergic beta-Antagonists; D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D011433:Propranolol; D010646:Phentolamine