Vascular actions of an inhffiltor of substance P amidation

Substance P (SP) relaxes vascular tissue by stimulating endothelial cell (EC) nitric oxide synthase. A two enzyme system [peptidylglycine α-nx>nooxygenasc(PAM) and peptidylamidoglycolate lyase (POL)] which converts glycine-extended precursors to active nmidatcd peptides, such as SP, has been discovered in EC (Oldham et al., 1992). Our aim was to determine whether a SP precursor can be processed within EC and subsequently act on the EC and the vasculature. Isolated intact rat aortic strips perfused in Krebs solution were preconstricted with phenylephrine (PE) and then exposed to graded concentrations of SP or its glycineextended precursor, SP-Gly (10^-8 - 10^-3 M) at 10 rain, intervals. The degree of relaxation was monitored. Both agents produced a comparable degree of vasorelaxation. In other aortas pretreated with an inhibitor of PAM, 4-phenyl-3-butenoic acid (PBA) at 10^-5 M for 30 min., we also examined the ability of SP or SP-Gly to produce vasorelaxation after PE contraction. The PBA markedly reduced the vasorelaxation to SP-Gly (-80%). However, it did not alter the vasorelaxing response to SP. PBA also reduced PE contraction by -45%. In isolated bovine EC, PBA (105M) also reduced basal nitric oxide synthase activity (L-arginine to L-citrulline conversion) by -28%. We conclude that EC can process a precursor of SP to an active peptide capable of relaxing vascular muscle. Thus, locally produced SP may modulate EC and vascular function.