Korean J Pain.  2007 Jun;20(1):21-25. 10.3344/kjp.2007.20.1.21.

The Role of Opioid Receptor on the Analgesic Action of Intrathecal Sildenafil in Rats

• Lee HG
• Jeong CY
• Yoon MH
• Kim WM
• Shin SH
• Kim YO
• Huang LJ
• Cui JH

• KMID: 2278035
• DOI: http://doi.org/10.3344/kjp.2007.20.1.21

Abstract

BACKGROUND: Intrathecal sildenafil has produced antinociception by increasing the cGMP through inhibition of phosphodiesterase 5. Spinal opioid receptor has been reported to be involved in the modulation of nociceptive transmission. The aim of this study was to examine the role of opioid receptor in the effect of sildenafil on the nociception evoked by formalin injection.
METHODS
Rats were implanted with lumbar intrathecal catheters. Formalin testing was used as a nociceptive model. Formalin-induced nociceptive behavior (flinching response) was observed. To clarify the role of the opioid receptor for the analgesic action of sildenafil, naloxone was administered intrathecally 10 min before sildenafil delivery, and formalin was then injected 10 min later.
RESULTS
Intrathecal sildenafil produced dose-dependent suppression of flinches in both phases during the formalin test. Intrathecal naloxone reversed the analgesic effect of sildenafil in both phases.
CONCLUSIONS
Sildenafil is active against the nociceptive state that's evoked by a formalin stimulus, and the opioid receptor is involved in the analgesic action of sildenafil at thespinal level.

Keyword

analgesia; cyclic guanosine monophosphate; opioid receptor; phosphodiesterase; sildenafil; spinal cor

MeSH Terms

Analgesia
Animals
Catheters
Cyclic Nucleotide Phosphodiesterases, Type 5
Formaldehyde
Naloxone
Nociception
Pain Measurement
Rats*
Receptors, Opioid*
Sildenafil Citrate
Cyclic Nucleotide Phosphodiesterases, Type 5
Formaldehyde
Naloxone
Receptors, Opioid