The Inhibitory Effect of Bupivacaine on Prostaglandin E 2 (EP 1 ) Receptor Functioning: Mechanism of Action

Prostaglandin E 2 receptors, subtype EP 1 (PGE 2 EP 1 ) have been linked to several physiologic responses, such as fever, inflammation, and mechanical hyperalgesia. Local anesthetics modulate these responses, which may be due to direct interaction of local anesthetics with PGE 2 EP 1 receptor signaling. We sought to characterize the local anesthetic effects on PGE 2 EP 1 signaling and elucidate mechanisms of anesthetic action. In Xenopus laevis oocytes, recombinant expressed PGE 2 EP 1 receptors were functional (half maximal effect concentration, 2.09 ± 0.98 X 10 -6 M). Bupivacaine, after incubation for 10 min, inhibited concentration-dependent PGE 2 EP 1 receptor functioning (half-maximal inhibitory effect concentration, 3.06 ± 1.26 × 10 6 M). Prolonged incubation in bupivacaine (24 h) inhibited PGE 2 -induced calcium-dependent chloride currrents (I Cl(Ca) ) even more. Intracellular pathways were not significantly inhibited after 10 min of incubation in bupivacaine. But I Cl(Ca) activated by intracellular injection of GTPγS (a nonhydrolyzable guanosine triphosphate [GTP] analog that activates G proteins, irreversible because it cannot be dephosphorylated by the intrinsic GTPase activity of the a subunit of the G protein) was reduced after 24 h of incubation in bupivacaine, indicating a G protein-dependent effect. However, inositol 1,4,5-trisphosphate-and CaCl 2 -induced I Cl(Ca) were unaffected by bupivacaine at any time points tested. Therefore, bupivacaine's effect is at phospholipase C or at the G protein or the PGE 2 EP 1 receptor. All inhibitory effects were reversible. We conclude that bupivacaine inhibited PGE 2 EP 1 receptor signaling at clinically relevant concentrations. These effects could, at least in part, explain how local anesthetics affect physiologic responses such as fever, inflammation, and hyperalgesia during the perioperative period.