Myogenic Tone and Reactivity of the Rat Ophthalmic Artery

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 microm, 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. NG-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.