Substance P Antagonists and Analgesia: Do They or Don’t They?

Substance P, an undecapeptide, is present in high concentrations in the dorsal horn of the spinal cord in thin afferent fibers (presumably C-fibers) associated with the transmission of noxious information [1,2]. Administered intrathecally, substance P has been reported to produce a transient hyperalgesia [3] and to induce behavioral responses suggested to be characteristic of noxious stimulation [4]. These pieces of evidence all support the suggestion that substance P has an excitatory role in neural transmission involving spinal nociceptive pathways.