Substance P (SP) is released from sensory nerves in arteries and heart. It activates neurokinin-1 receptors (NK1R) causing vasodilation, immune modulation, and adverse cardiac remodeling. The hypothesis was tested that SP and SP metabolites activate different second messenger signaling pathways. Macrophages, endothelial cells and fibroblasts metabolized SP to N- and C-terminal metabolites to varying extents. SP 5-11 was the most abundant metabolite followed by SP 1-4, SP 7-11, SP 6-11, SP 3-11 and SP 8-11. In NK1R expressing HEK293 cells, SP and some C-terminal SP metabolites stimulate the NK1R promoting dissociation of several Ga proteins including Gas and Gaq from their bg subunits. SP increases intracellular calcium concentrations ([Ca]i) and cyclic AMP (cAMP) accumulation with similar -log EC50 values of 8.5±0.3 and 7.8±0.1 M, respectively. N-Terminal metabolism of SP by up to 5 amino acids and C-terminal deamidation of SP produce peptides that retain activity to increase [Ca]i but not to increase cAMP. C-Terminal metabolism results in loss of both activities. Thus, [Ca]i and cAMP signaling are differentially affected by SP metabolism. To assess the role of N-terminal metabolism, SP and SP 6-11 were compared on cAMP-mediated activities in NK1R expressing 3T3 fibroblasts. SP inhibits NFkB activity, cell proliferation and wound healing and stimulates collagen production. SP 6-11 had little or no activity. COX-2 expression is increased by SP but not SP 6-11. Thus, metabolism may select the cellular response to SP by inhibiting or re-directing the second messenger signaling pathway activated by the NK1R.