Sensory neuropeptide effects in human skin

Neuropeptides released from sensory nerves may account for cutaneous flare and wheal following local trauma. In 28 normal subjects we have studied the effects of four sensory neuropeptides given by intradermal injection on the forearm or back. All peptides caused a flare distant from the site of injection, presumably due to an axon reflex. Substance P (SP) was the most potent (geometric mean dose causing 50% of maximum flare, 4.2 pmol). Neurokinin A (NKA) was the next most potent with neurokinin B (NKB) and calcitonin gene‐related peptide (CGRP) the least. The distant flare response to SP, NKA and NKB was maximal at 5 min and disappeared within 2 h. CGRP caused a local erythema over the site of injection at doses above 0.5 pmol which at higher doses lasted for up to 12 h. SP, NKA and NKB caused wheals at doses above 5 pmol with SP and NKB being the most potent. CGRP (up to 250 pmol) did not consistently cause wheal formation. There was no significant effect of coinjection of CGRP upon the response to SP although there was a tendency for an enhancement of the wheal response. The H 1 ‐histamine antagonist terfenadine (60 mg orally) significantly inhibited the wheal and distant flare response to histamine (5 nmol) and NKA, but not that caused by NKB. The distant flare of CGRP was also reduced but the local erythema was unaltered. Aspirin (600 mg orally) significantly inhibited the distant flare response to SP, NKA and CGRP, but not that caused by NKB or histamine; the local erythema induced by CGRP was unaffected by aspirin. Aspirin also inhibited the wheal formed by NKA but not the wheal induced by the other substances. These results suggest that tachykinins cause a distant flare response partially via the release of histamine and cyclo‐oxygenase products, but cause a wheal by a direct effect on the skin microvasculature. The order of potency SP > NKB > NKA suggests that an SP p or NK l receptor is involved in the wheal response. CGRP by contrast has a direct vasodilator effect which is very prolonged.