Neurokinin receptors could be differentiated by their capacity to respond to the transglutaminase-synthesized gamma-(glutamyl5)spermine derivative of substance P.

Four different gamma-(glutamyl5)amine derivatives of substance P (SP) were synthesized in vitro in the presence of purified guinea pig liver transglutaminase and Ca2+. The 1,3-diaminopropane, spermidine, spermine (Spm), and monodansylcadaverine adducts of the neuropeptide were purified by HPLC on a reversed-phase column and characterized by fast atom bombardment mass spectrometry. The gamma-(glutamyl5)Spm derivative of SP (Spm-SP) was found to be able, like the parent neuropeptide, to provoke rabbit aorta relaxation, to decrease rat arterial blood pressure, and to inhibit collagen-induced platelet aggregation. Unlike SP, only a weak inflammatory response was observed when Spm-SP was injected in the rat hind limb. All these effects were found to be prevented by N omega-nitro-L-arginine methyl ester, a well-known nitric oxide synthesis inhibitor. In contrast, Spm-SP was completely ineffective in contracting guinea pig ileal segments, thus confirming our preliminary observations indicating that Spm-SP does not evoke SP-like spasmogenic effects on isolated smooth muscle preparations. The specificity of the effects due to the selective introduction of a Spm moiety at the glutamine5 level was demonstrated by the SP agonist pharmacological profile of the other gamma-(glutamyl5)amine derivatives tested. These results suggest that neurokinin receptors could be differentiated by their capacity to respond to Spm-SP.