Intradermal administration of sumatriptan (5 µg/paw) 15 min prior to endothelin, attenuated endothelin hyperalgesia and stimulus-induced enhancement of endothelin hyperalgesia (A, for both P < 0.001, two way repeated measures ANOVA followed by Bonferroni post test, n = 8/group), whereas sumatriptan treatment 15 min prior to epinephrine, only attenuated stimulus-induced enhancement of epinephrine hyperalgesia (B, P < 0.001, two way repeated measures ANOVA followed by Bonferroni post test, comparing results within and between groups at different time points, n = 8/group). Intradermal administration sumatriptan 15 min prior to PGE2 (100 ng) had no effect on PGE2 hyperalgesia (C, n = 6).