Effects of a substance P analogue with antagonist properties ([D-Arg1, D-Trp7,9, Leu11]substance P) on spontaneous activity of the adrenal sympathetic nerve and its evoked reflex discharges in response to somatic afferent stimulation.

The present study was designed to test the effect of a substance P (SP) antagonist, [D-Arg1, D-Trp7,9, Leu11]substance P (Spantide), on spontaneous efferent activity of adrenal sympathetic nerve and the two A- and C-sympathetic reflex components evoked in adrenal sympathetic nerve by stimulation of myelinated A- and unmyelinated C-afferent nerve fibers of a hindlimb nerve, respectively, in anesthetized rats. The spontaneous adrenal nerve activity and both of the A- and C-sympathetic reflex components were proportionally reduced by intrathecal application of the SP antagonist (0.038-0.76 nmol), although the same doses did not affect A- and C-somatic reflex components. These data suggest that the SP antagonist has a greater effect on SP-containing neurons related to the generation of spontaneous activity of sympathetic neurons and somato-sympathetic reflex pathways than on SP-containing primary somatic afferent nerves and somato-somatic reflex pathways.