Calcitonin gene-related peptide, substance P and nitric oxide are involved in cutaneous inflammation following ultraviolet irradiation

Abstract

Evidence from our previous work suggests that neurogenic mediators contribute to the inflammation following ultraviolet (UV) irradiation of the skin. We have investigated whether calcitonin gene-related peptide (CGRP), substance P and nitric oxide (NO) participate in the cutaneous inflammatory reaction of the rat hind paw and ear to UV irradiation. Skin blood flow was measured by laser Doppler technique. Oedema was quantified using a spring loaded micrometer to measure ear thickness. UV irradiation of the rat skin lead to a long lasting increase in skin blood flow. This increase was dose dependently attenuated by the CGRP receptor antagonist CGRP-(8–37) (0.15 nmol in 25 μl to 6.0 nmol in 25 μl, s.c.) up to 51% with a maximum of effectiveness at 24 h post irradiation. The inhibitor of NO synthase $\text{N}{}^{\mathrm{<mtext>G</mtext>}}\text{-}\text{nitro}\text{-}\text{L}\text{-}\text{arginine}$ methyl ester hydrochloride (L-NAME, 25 nmol in 25 μl, s.c.) attenuated skin blood flow by 38%. Concurrent injections s.c. of CGRP-(8–37) (1.5 nmol in 12.5 μl) and L-NAME (25 nmol in 12.5 μl) demonstrated an augmentive effect in attenuating skin blood flow. The tachykinin NK₁ receptor antagonist CP-96,345 (6.0 nmol in 25 μl, s.c.) attenuated skin blood flow by 27%. $\text{N}{}^{\mathrm{<mtext>G</mtext>}}\text{-}\text{Nitro}\text{-}\text{D}\text{-}\text{arginine methyl}$ ester hydrochloride (D-NAME) and CP-96,344 showed no effects on skin blood flow after UV irradiation. CGRP-(8–37) (0.6 nmol in 10 μl) i.d. and L-NAME (10 nmol in 10 μl) i.d. had no effect of oedema formation after UV irradiation. Furthermore, post UV irradiation enhanced CGRP- and NO synthase-immunoreactivity in nerve fibres in the exposed skin area were visible. Taken these findings together we suggest the involvement of the neuropeptides CGRP and substance P and of neuronal NO on the vasodilatory component of the UV-induced inflammatory reaction of the rat skin. CGRP contributing to UV-induced vasodilation acts in an endothelial NO-independent manner.