Inflammatory mediators do not stimulate CGRP release if prostaglandin synthesis is blocked by S(+)-flurbiprofen in isolated rat skin.

OBJECTIVE: Nonsteroidal antiinflammatory drugs are well known as antipyretic analgesics, however, their mode of action is not yet fully understood. Besides their cyclooxygenase (COX) blocking effect other action principles are discussed. In the present study we investigated the effects of the flurbiprofen enantiomers on the stimulated release of calcitonin gene-related peptide (CGRP) from the isolated rat skin as an indirect measure of peripheral nociceptor activation and 'neurogenic inflammation'. METHODS: Stimulation was performed by a combination of inflammatory mediators (bradykinin, serotonin and histamine, all 10(-5) M). In addition, prostaglandin E(2) (PGE(2)) release was determined in order to verify the inhibitory effect of the tested drugs on prostaglandin production. RESULTS: S(+)-flurbiprofen (10(-7) and 10(-6) M), reported as the COX blocking enantiomer, completely blocked basal as well as stimulated PGE(2) release. Under R(-)-flurbiprofen a reduction of basal PGE(2) release was not significant; the stimulated PGE(2) release, was however significantly reduced at 10(-7) M and completely suppressed at 10(-6) M drug concentration. The stimulated CGRP release was not affected by R(-)-flurbiprofen (10(-7) or 10(-6) M). In contrast, S(+)-flurbiprofen - only at 10(-6) M - significantly reduced the inflammatory mediator-induced CGRP release. This reduction could be reversed by co-administration of PGE(2) (10(-5) M) suggesting that the effect was due to COX block and prostanoid deprivation. CONCLUSION: Although a higher concentration of the effective enantiomer was needed to inhibit stimulated CGRP than PGE(2) release, flurbiprofen seems to exert the antinociceptive/antiinflammatory effects observed by preventing the secondary cutaneous prostaglandin formation that appears necessary to enable activation by inflammatory mediators of the CGRP-releasing nerve fibers.

N- and L- but not P/Q-type calcium channels contribute to neuropeptide release from rat skin in vitro.

Here we directly demonstrate the liberation of CGRP from rat skin in vitro induced by high extracellular concentrations of KCl. The EC50 was 52 mM KCl and saturation was reached from 80 mM KCl. The release was entirely dependent on the presence of extracellular calcium ions. It was reduced by nonsubtype selective inhibition of voltage-operated calcium channels (VOCCs). Application of selective antagonists suggest expression of L-type and N-type but not P/Q-type VOCCs in cutaneous nociceptive terminals. These may be activated by any suprathreshold depolarizing stimuli to induce neurogenic inflammation. The expression pattern greatly differs from central nociceptive terminals where, in addition, P/Q-type VOCC have been found.

Inflammatory mediators release calcitonin gene-related peptide from dorsal root ganglion neurons of the rat.

The interactions between the inflammatory mediators bradykinin, serotonin, prostaglandin E(2) and acid pH were studied in rat dorsal root ganglion neurons in culture. For this purpose, the cultures were stimulated by inflammatory mediators (bradykinin, serotonin, prostaglandin E(2), 10(-5)M each) or acid solution (pH 6.1) for 5 min and the content of calcitonin gene-related peptide was determined in the supernatant before, during and after stimulation, using an enzyme immunoassay. Acid solution resulted in a threefold increase of the basal calcitonin gene-related peptide release which was entirely dependent on the presence of extracellular calcium. The release could not be blocked by the addition of the capsaicin antagonist capsazepine (10(-5)M). Bradykinin (10(-5)M) caused a 50% increase of the basal calcitonin gene-related peptide release which was again dependent on the presence of extracellular calcium, whereas serotonin and prostaglandin E(2) were each ineffective at 10(-5)M concentration. The combination of bradykinin, serotonin and prostaglandin E(2) led to a fivefold increase of the calcitonin gene-related peptide release which could not be further enhanced by acidification. The competitive capsaicin receptor antagonist capsazepine (10(-5)M) significantly reduced the release induced by the combination of bradykinin, serotonin and prostaglandin E(2). It is suggested that the inflammatory mediators co-operate and together may act as endogenous agonists at the capsaicin receptor to cause calcium influx and consecutive neuropeptide release.