Abstract
Purpose: To assess the role of esmolol, a β1 receptor blocker, in the modulation of pain in the absence of anesthesia.
Methods: Rats were chronically instrumented to record mean arterial blood pressure (MAP) and heart rate (HR). Animals were divided into three groups. Group 1 [esmolol high (EH) 150 mg·kg−1·hr−1; n=9], Group 2 [esmolol low (EL) 40 mg·kg−1·hr−1; n=7] and Group 3 saline (n=9). Formalin 5% was injected in the rat hind paw. Formalin-induced lifting, MAP and HR were recorded at five minute intervals for 35 min after formalin injection.
Results: Formalin was associated with an early (Phase 1; 0–5 min) and late nociceptive response (Phase 2; 10–35 min). Esmolol did not affect Phase 1. Although low dose esmolol had minimum effects on nociceptive Phase 2, it was diminished with high dose esmolol. Formalin induced biphasic increases in MAP and HR. Although esmolol did not affect the initial increase in MAP, high dose esmolol blunted the secondary increase in MAP. Both low and high doses of esmolol inhibited formalin-induced tachycardia during the first 30 min.
Conclusion: Our data suggest that esmolol leads to analgesia and reduction of cardiovascular responses to pain.
Résumé
Objectif: Cette étude a été réalisée pour étudier le rôle de l’esmolol, un bloqueur des récepteurs béta 1 dans la modulation de la douleur en l’absence d’anesthésie.
Méthode: Des rats ont été instrumentés pour enregistrer la tension artérielle moyenne (TAM), et la fréquence cardiaque (FC). Les animaux ont été divisés en 3 groupes. Le groupe 1 [esmolol à la dose de 150 µg·kg−1·hr−1; n=9], le groupe 2 [esmolol à la dose de 40 µg·kg−1·hr−1; n=7] et le groupe 3 [chlorure de sodium isotonique; n=9]. Le formol (5%) a été injecté par voie sous-cutanée dans la patte du rat. Les mouvements de la patte ainsi que la TAM et la FC ont été enregistrés à 5 min d’intervalles pendant 35 min après l’injection du formol.
Résultats: L’activité physique qui accompagnait l’administration de formol a été représentée par une phase immédiate (Phase 1; 0–5 min) et une phase secondaire (Phase 2; 10–35 min). L’esmolol n’a pas produit d’effets significatifs sur les mouvements de la patte en Phase 1. Alors qu’à faible dose, l’esmolol n’a provoqué que peu d’effets sur les mouvements de la patte en Phase 2, à forte dose il a engendré une réponse significative. Le formol a produit des augmentations significatives de la TAM et de la FC. Bien que l’esmolol, à forte dose, n’a pas produit de changements significatifs sur la TAM, il a fortement diminué l’augmentation secondaire de la TAM. Les 2 doses d’esmolol ont diminué la tachycardie provoquée par l’injection de formol.
Conclusion: Nos résultats suggèrent que l’administration d’esmolol s’associe à une diminution de l’hyperactivité liée à l’injection de formol dans la patte.
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Work performed in the Anesthesiology Department, University of Texas Medical School, Houston, Texas, USA.
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Davidson, E.M., Doursout, MF., Szmuk, P. et al. Antinociceptive and cardiovascular properties of esmolol following formalin injection in rats. Can J Anaesth 48, 59–64 (2001). https://doi.org/10.1007/BF03019816
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DOI: https://doi.org/10.1007/BF03019816