Effect of Ropivacaine on Lip Blood Flow in Rats

Objectives: Besides their neurally blocking effects, local anesthetics may show effects on the peripheral vasculature. By and large they are vasoconstrictors in low concentrations and vasodilators in higher concentrations, clinically used concentrations. Ropivacaine (Anapeine^®, AstraZeneca, Osaka, Japan) is a long-acting amino-amide local anesthetic agent. We investigated lip blood flow changes after intra-labial injection of ropivacaine in various concentrations. Methods: Approval from the Institutional Animal Care Committee of our university was obtained before the commencement of this study. Subjects were male Wistar rats. Twenty µl of various concentrations of ropivacaine (0.125, 0.25, 0.5, 0.75 and 1%) were injected into the upper lip under general anesthesia with intraperitoneal pentobarbital. Injections of saline, 2% lidocaine and 10 µg/ml adrenaline served as controls. The lip blood flow was measured from 0.5 to 60 minutes after injection by laser Doppler flowmeter with a contact probe. Results: The concentrations of ropivacaine lower than 0.75% showed a reduction in lip blood flow compared with saline, this being more pronounced with the lowest concentration (0.125%). But the flow was larger than the effect of adrenaline. However, 1% ropivacaine, the highest concentration in clinical use, reduced the flow almost the same degree as the effect of 10 µg/ml adrenaline. The vasoconstrictive effect of ropivacaine in various concentrations lasted longer compared with adrenaline; from 10 to 60 minutes in ropivacaine, and from 0.5 to 50 in adrenaline. Conclusions: Ropivacaine reduced lip blood flow in rats. The reduction showed dose-response relationship in concentrations lower than 0.75%. One percent ropivacaine showed strong vasoconstrictive effect on the rat lip vasculature.