Substance P and calcitonin gene-related peptide in the chicken skin: distribution and cardiovascular effects.

A short vasodilatation but no plasma extravasation could be induced by antidromic stimulation of peripheral nerves in the chicken skin. Since in mammalian species the sensory neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP) are involved in this mechanism, the distribution and the cardiovascular effect of these peptides were investigated in the chicken. In the skin, SP- and CGRP-immunoreactivity was found co-localized in the epidermis and dermis. On blood vessels, however, SP positive but CGRP negative nerve rfibres were observed. Systemic (i.v.) and local close arterial injection of SP produced dose-dependent cutaneous vasodilatation with threshold doses of 6.5 pmol/kg or 1 pmol, respectively. Neurokinin A and acetylcholine were about 20 to 50-fold less effective, when injected close arterially. Systemic injection of SP (5-1800 pmol/kg) dose-dependently evoked a short fall in blood pressure which was followed by a longer lasting pressor response. CGRP up to 800 pmol/kg did not change blood pressure but produced a pronounced tachycardia. Close arterial injection of CGRP resulted in variable bi- or triphasic vascular responses which consisted of vasodilatations and also vasoconstriction with thresholds between 0.25 and 65 pmol. The data also indicate that in the chicken, SP, and to a lesser extent CGRP, can be involved in antidromic vasodilatation.