Role of ET(A) and ET(B) endothelin receptors on endothelin-1-induced potentiation of nociceptive and thermal hyperalgesic responses evoked by capsaicin in rats

Neurosci Lett. 2009 Jul 3;457(3):146-50. doi: 10.1016/j.neulet.2009.03.055. Epub 2009 Mar 21.

Abstract

Increasing evidence indicates that endothelin-1 (ET-1) activates nociceptive neurons and sensitizes them to different noxious stimuli, but involvement of TRPV1-dependent mechanisms in mediation of such effects is not yet fully understood. Here we report that intraplantar (i.pl.) injection of ET-1 (10 pmol) into the hind paw of rats induced overt nociceptive behavior over the first hour, followed by a slowly developing thermal hyperalgesia, lasting from 3 to 8h after injection. Both effects were also induced by similar injections of capsaicin (10-1000 pmol), but these responses were shorter lasting than those caused by ET-1. Local pre-treatment with the TRPV1 antagonist capsazepine (30 nmol, i.pl.) reduced only the thermal hyperalgesia induced by ET-1, but fully suppressed both responses to capsaicin (1000 pmol). Injection of a sub-threshold dose of ET-1 (0.1 pmol, i.pl.) prior to capsaicin (1 pmol, i.pl.) markedly sensitized the hind paw to the overt nociceptive and thermal hyperalgesic effects of the later. The potentiation of capsaicin-induced nociception by ET-1 was abolished by prior i.pl. injection of BQ-123 (ET(A) receptor antagonist, 10 nmol), but unaffected by BQ-788 (ET(B) receptors antagonist, 10 nmol), whereas the enhancement of capsaicin-induced hyperalgesia by ET-1 was attenuated by both antagonists. Therefore, differently to what has been reported in mice, in rats TRPV1 receptors contribute selectively to thermal hyperalgesia, but not overt nociception, induced by ET-1. Importantly, although ET-1 augments capsaicin-induced overt nociception and thermal hyperalgesia, potentiation of the former relies solely on ET(A) receptor-mediated signaling mechanisms, whereas both receptors contribute to the latter.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Analysis of Variance
  • Animals
  • Capsaicin / analogs & derivatives
  • Capsaicin / pharmacology*
  • Dose-Response Relationship, Drug
  • Endothelin A Receptor Antagonists
  • Endothelin B Receptor Antagonists
  • Endothelin-1 / metabolism*
  • Hindlimb / drug effects
  • Hyperalgesia / chemically induced
  • Hyperalgesia / physiopathology*
  • Male
  • Oligopeptides / pharmacology
  • Pain Measurement
  • Peptides, Cyclic / pharmacology
  • Physical Stimulation
  • Piperidines / pharmacology
  • Rats
  • Rats, Wistar
  • Receptor, Endothelin A / metabolism*
  • Receptor, Endothelin B / metabolism*
  • Sensory System Agents / pharmacology*
  • TRPV Cation Channels / antagonists & inhibitors
  • Temperature

Substances

  • Endothelin A Receptor Antagonists
  • Endothelin B Receptor Antagonists
  • Endothelin-1
  • Oligopeptides
  • Peptides, Cyclic
  • Piperidines
  • Receptor, Endothelin A
  • Receptor, Endothelin B
  • Sensory System Agents
  • TRPV Cation Channels
  • Trpv1 protein, rat
  • BQ 788
  • capsazepine
  • Capsaicin
  • cyclo(Trp-Asp-Pro-Val-Leu)