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Myogenic Tone and Reactivity of the Rat Ophthalmic Artery

From the Department of Pharmacology and Therapeutics, Vascular Biology and Cell Physiology Group, College of Medicine, and McKnight Brain Institute, University of Florida, Gainesville, Florida.

PURPOSE. To study and quantify myogenic behavior and reactivity of the rat ophthalmic artery to pressure and different vasoactive substances in vitro.

METHODS. Rat ophthalmic arteries (diameter of 217 ± 6 µm, n = 22) were isolated, cannulated with glass pipettes in an arteriograph and pressurized in a physiological buffer. Internal diameter was continuously monitored. The effect of intraluminal pressure on the diameter was assessed and concentration–response curves to different constrictor and dilator agonists were obtained at an intraluminal pressure of 70 mm Hg.

RESULTS. Myogenic tone developed at an intraluminal pressure of 30 to 40 mm Hg, continued to increase, and was maintained up to a pressure of 199 mm Hg in these arteries. Arteries dilated and constricted in response to 16 and 60 mM potassium, respectively. Endothelin-1 was the most potent and efficacious constrictor, with a biphasic concentration–response curve, followed by vasopressin, serotonin, U-46619 and phenylephrine. Carbachol was the most efficacious dilator, followed by isoprenaline. The peptide dilators calcitonin gene-related peptide (CGRP) and vasoactive intestinal peptide (VIP) were potent but less efficacious than carbachol and isoprenaline. Histamine and adenosine were even less potent and less efficacious dilators. N^G-nitro-L-arginine methyl ester (L-NAME) constricted and indomethacin dilated the arteries.

CONCLUSIONS. This study provides the first direct evidence for myogenic autoregulatory properties and pharmacological heterogeneity in the rat ophthalmic artery.

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