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A991
October 17, 2011
8:00:00 AM - 11:00:00 AM
Room Hall B2 Area G
Cinnamaldehyde Prolongs Cutaneous Analgesia of Local Anesthetics in Rats
Chien-Chung Huang, M.D., Hsu-Tin Won, M.S., Jen-Kun Cheng, M.D.,Ph.D., Chien-Chuan Chen, M.D., Yu-Chun Hung, M.D.
Mackay Memorial Hospital, Taipei city, Taiwan
Background and objectives: Cinnamaldehyde is an organic compound from cinnamon bark and contributes to flavor and odor of cinnamon. It serves as an agonist of transient receptor potential ankyrin subfamily member 1 (TRPA1), which is a nonselective cation channel expressed in nociceptors. It is wildly accepted that TRPA1 agonists, similar to a transient receptor potential vanilloid type 1 activator (capsaicin), enhance inhibitory as well as excitatory synaptic transmission in nervous system. For example, cinnamaldehyde elicited heat and mechanical hyperalgesia, and cold hypoalgesia as well. Recent studies have suggested that a prolonged blockade can be achieved via capsaicin along with local anesthetics. However, the role of TRPA1 agonists on cutaneous analgesia remains unclear. Therefore, we investigated whether cinnamaldehyde prolongs cutaneous analgesia when co-administrated with local anesthetics.

Methods: Male Sprague-Dawley rats (weights 250-300 g) anesthetized with isoflurane, and 0.6ml drug solutions of 0.5% lidocaine, 0.0625% bupivacaine, and cinnamaldehyde in selected concentrations were injected subcutaneously via rat shaved dorsal skin respectively (n = 8 per group). In combination groups, cinnamaldehyde were given 10 minutes after application of lidocaine or bupivacaine. The inhibition of the cutaneous trunci muscle reflex was evaluated by pinpricks. For toxicity evaluation, skin was excised from euthanized rats, and stained with hematoxylin and eosin.

Results: Cinnamaldehyde alone provided a dose-dependent block to pinpricks. The time to full recovery were 43.13±5.97,63.75±4.7 and 95.63±3.94 minutes (mean±SE) in 0.5%,1% and 2% cinnamaldehyde respectively. Complete block to pinpricks accomplished in 2% cinnamaldehyde with 0.5% lidocaine and with 0.0625% bupivacaine, and the time to full recovery were 157.5±5.67 and 159.38±6.3 minutes which were significantly prolonged compared to lidocaine or bupivacaine alone. In histology, there were some lymphocytic infiltrations approximately 2 days after treatment which indicated inflammation around the injected area.

Conclusions: The combined application of cinnamaldehyde and local anesthetics produced a markedly prolonged cutaneous nociceptive block in rats when compared with either agent alone. A dose-dependent prolongation was observed while high concentrations of cinnamaldehyde augment duration of cutaneous analgesia. The mechanisms through which cinnamaldehyde affects the duration have not yet to be elucidated. Further researches are needed to the safety of clinical usage.

Copyright © 2011 American Society of Anesthesiologists