Substance P is a member of the tachykinin family of peptides, and has classically been considered a neuropeptide, secreted predominantly by neuronal cells of the central and peripheral nervous systems. Interaction with tachykinin receptors on vascular endothelial or smooth muscle cells can cause vasodilation or contraction, respectively. Furthermore, the presence of this peptide in the nervous system can have a variety of effects on behaviorand the transmission of pain. These effects of substance P have been reviewed (Pernow. 1983; Maggi. 1996; Holzer and Holzer-Petsche. 1997; Quarter a and Maggi. 1998).