The latex of the wild growing plant Calotropis procera
produces inflammation of the skin and mucous membranes upon
accidental exposure. On local administration it elicits an intense
inflammatory response due to the release of histamine and
prostaglandins that is associated with hyperalgesia. In the
present study we have evaluated the anti-inflammatory and
antinociceptive activity of oxytocin and melatonin against rat
paw edema induced by dried latex (DL) of C procera and
compared it with that against carrageenan-induced paw edema.
Aqueous extract of DL of C procera or carrageenan (1%)
was injected into the subplantar surface of the rat paw and the
paw volume was measured at 0, 1, 2, 3, 4, 6, 10, and 24 hours. The
associated hyperalgesic response and functional impairment were
also evaluated concomitantly by dorsal flexion pain test, motility
test, and stair climbing ability test. The inhibitory effect of
oxytocin and melatonin on edema formation and hyperalgesic
response was compared with dexamethasone. DL-induced edema
formation was maximum at 2 hours and was associated with decreased
pain threshold and functional impairment. Treatment with melatonin
significantly attenuated the edematous response while both
oxytocin and melatonin increased the pain threshold and improved
functional parameters. Both oxytocin and melatonin significantly
inhibited the hyperalgesia associated with DL-induced paw edema.
Oxytocin was found to be as effective as melatonin in ameliorating
the hyperalgesic response. However, it was found to be less
effective than melatonin in attenuating edema formation.
