Involvement of neurokinins in antidromic vasodilatation in hairy and hairless skin of the rat hindlimb

By intravenous application of the specific neurokininl receptor antagonist SR 140333 and the specific calcitonin gene-related peptide receptor antagon ist CGRP(8-37) we tested to what extent neurokinins (substance P, neurokini n A) and calcitonin gene-related peptide are involved in mediating antidrom ic vasodilatation in skin of anaesthetized Wistar rats. The lumbar sympathe tic chain was sectioned bilaterally between ganglia L2 and L3 to remove ong oing vasoconstrictor activity to the hindquarter. The left dorsal root L5 w as stimulated electrically at 1 Hz with 20 pulses supramaximal for activati ng C-fibres to evoke antidromic vasodilatation which was measured with lase r Doppler flowmetry on the glabrous plantar skin and the hairy skin of the lower hindlimb within the left L5 territory. Stimulation-induced vasodilata tion was tested after applying SR 140333 (0.1 mg/kg) and CGRP(8-37) (0.3 mg /kg) alone or in combination. SR 140333 delayed the onset of the vasodilata tion, but did not change its amplitude. CGRP(8-37) reduced the amplitude an d duration of the vasodilatation, but did not affect the latency of its ons et. In combination, SR 140333 potentiated the effect of CGRP(8-37) on the a mplitude of the vasodilatation in glabrous but not in hairy skin and CGRP(8 -37) potentiated the delayed onset produced by SR 140333 in both cutaneous tissues. Antidromic vasodilatation in glabrous skin was almost totally bloc ked by SR 140333 (0.1 mg/kg) in combination with CGRP(8-37) (0.45 mg/kg), b ut a substantial dilatation remained in hairy skin. It is concluded that in rat glabrous skin the vasodilatation evoked by a lo w level of activity in small-diameter primary afferents is likely to result from the release and synergistic action of neurokinins (substance P and/or neurokinin A) and calcitonin gene-related peptide, while in hairy skin neu rokinins are involved to a minor extent only. (C) 1999 IBRO. Published by E lsevier Science Ltd.