EFFECTS OF LIDOCAINE AND BUPIVACAINE ON ISOLATED RABBIT MESENTERIC CAPACITANCE VEINS

Background and Objectives. The direct effects of circulating lidocaine and bupivacaine on splanchnic capacitance veins have not been examine d previously. This article reports on the effects of clinically releva nt concentrations of lidocaine and bupivacaine on adrenergic responsiv eness of isolated rabbit mesenteric veins and examines the mechanism o f changes. Methods. Rings of ileal mesenteric capacitance veins were s uspended in tissue baths for isometric tension measurements. Effects o f lidocaine and bupivacaine on contractile responses to adrenergic ner ve stimulation, exogenous norepinephrine (10(-6) M NE), and potassium chloride (80 mM KCl) were examined in endothelium-intact, L-NAME (10(- 4) M) treated or denuded veins. Results. Constriction in response to a drenergic nerve stimulation was attenuated by lidocaine and bupivacain e in a dose-dependent manner, with the potency of bupivacaine being hi gher than lidocaine. Unstimulated or potassium-constricted veins with and without endothelium were unaffected by lidocaine (0.25-100 mu g/mL ) and bupivacaine (0.1-100 mu g/mL). In veins preconstricted by exogen ously administered NE, a cumulative increase of both anesthetics produ ced no effect at low doses, an augmentation of constriction to NE at 5 -20 mu g/mL bupivacaine and 20-100 mu g/mL lidocaine, and minimal effe ct at 50-100 mu g/mL bupivacaine. These actions persisted in denuded o r L-NAME treated veins. Nonincremental delivery of high concentrations of lidocaine or bupivacaine produced relaxation of NE and potassium-c onstricted rings in the absence and presence of L-NAME. Conclusions. L idocaine and bupivacaine in concentrations typical during uncomplicate d regional anesthesia inhibit adrenergic neurotransmission in rabbit m esenteric capacitance veins and produce modest venodilatation. Higher doses, resembling concentrations during accidental intravascular injec tion, result in substantial loss in vasomotor control of these capacit ance vessels, which may contribute to hemodynamic effects.