Interactions of inflammatory mediators stimulating release of calcitonin gene-related peptide, substance P and prostaglandin E 2 from isolated rat skin

Abstract

Inflammatory mediators acting directly on nociceptive primary afferents induce neuropeptide release. In this study we investigated interactions between bradykinin, serotonin, histamine, prostaglandin and acid pH in stimulating the release of substance P (SP), calcitonin gene-related peptide (CGRP) and prostaglandin E 2 (PGE 2) from isolated flaps of rat back skin using enzyme immunoassays. Stimulation with bradykinin (10 −5 M) augmented the release of SP, CGRP and PGE 2 significantly. Serotonin, histamine and PGE 2 individually tested (10 −5 M) had no effect on neuropeptide release but they facilitated the bradykinin-evoked neuropeptide release. When bradykinin was combined with both serotonin and histamine, neither additional PGE 2 nor acid pH showed any further effect, suggesting that the facilitation had reached a maximum. Exposure of the skin to acid pH (6.1 or 5.2) significantly increased CGRP release. SP release was only slightly enhanced and PGE 2 release, in contrast, was suppressed by low pH stimulation, probably due to pH-dependent inhibition of phospholipase A 2. Treatment of the rats with flurbiprofen (25 mg/kg i.p.) one hour before dissection reduced PGE 2 to detection level and inhibited the CGRP secretion evoked by the combination of bradykinin, serotonin and histamine (all 10 −6 M). As this suppression could not be overcome by substitution of PGE 2 (10 −6 M), it is likely that exogenously applied PGE 2 differs in effect from endogenous, intracellularly synthesized prostaglandins that are accompanied by active intermediates and byproducts.