Effect of ricinoleic acid in acute and subchronic experimental models of inflammation

OBSERVATIONAL studies indicate that topical application of ricinoleic acid (RA), the main component of castor oil, exerts remarkable analgesic and ant i-inflammatory effects. Pharmacological characterization has shown similari ties between the effects of RA and those of capsaicin, suggesting a potenti al interaction of this drug on sensory neuropeptide-mediated neurogenic inf lammation. The aim of this study was to assess RA anti-inflammatory activit ies in comparison with capsaicin in several models of acute and subchronic inflammation. The acute inflammation was induced by intradermal injection o f carrageenan in the mouse or by histamine in the guinea-pig eyelid. In eit her experiment, the extent of the oedema thickness was measured. Subchronic oedema was induced by complete Freund's adjuvant injection in the ventral right paw of mice. Tissue substance P (SP) was measured in the carrageenan experiments by radioimmunoassay (RIA). It was found that the acute topical application of RA (0.9 mg/mouse) or capsaicin (0.09 mg/mouse) significantly increased the mouse paw oedema induced by carrageenan, while an 8-day repe ated topical treatment with the same doses of both compounds resulted in a marked inhibition of carrageenan-induced paw oedema matched by a reduction in SP tissue levels. Similar effects were found against histamine-induced e yelid oedema in guinea-pigs after acute or repeated application of RA or ca psaicin. RA and capsaicin given for 1-3 weeks reduced the established oedem a induced by Freund's adjuvant, a subchronic model of inflammation, particu larly if given by the intradermal route. Either in mouse paw or in guineapi g eyelid, capsaicin but not RA by itself produced a slight hyperemia and ac tivation of a behavioural response (e.g. scratching of the eyelids). On the basis of the present results, RA may be seen as a new capsaicin-like, non- pungent anti-inflammatory agent suitable for peripheral application.