Paradoxic effects of propofol on visceral pain induced by various TRPV1 agonists.

Intraperitoneal injection of propofol inhibits subsequent acetic acid-induced writhing response in mice. Propofol increases the sensitivity of dorsal root ganglion neurons to capsaicin through transient receptor potential ankyrin subtype-1 (TRPA1) and protein kinase Cε (PKCε)-mediated phosphorylation of transient receptor potential vanilloid subtype-1 (TRPV1). Intraperitoneal co-injection of propofol may increase visceral nociception induced by TRPV1 agonists via sensitization of TRPV1. Therefore, we investigated the effects of intraperitoneal co-injection of propofol on nociception induced by acetic acid and capsaicin. The number of writhing movements induced by acetic acid or nociception time by capsaicin with or without propofol were counted. Neonatal capsaicin-treated mice were also used to demonstrate the role of TRPV1 in the effects of propofol on nociception, induced by TRPV1 agonists. Co-injection of propofol resulted in a pronociceptive effect on the writhing response induced by acetic acid, while the same dose of propofol ameliorated the response to capsaicin. The writhing response to intraperitoneal acetic acid was sharply inhibited following neonatal treatment with capsaicin. Co-injection with propofol reduced the number of writhing movements induced by acetic acid in neonatal capsaicin-treated mice. These results suggest that propofol binds to TRPV1 at the capsaicin-binding pocket.