Transglutaminase-synthesized gamma-(glutamyl(5)) spermidine derivative of substance P is a selective tool for neurokinin-2 receptors characterization

The ability of transglutaminase-synthesized 1,3-diaminopropane, spermidine (Spd), spermine (Spm). and monodansylcadaverine gamma-(glutamyl(5))derivatives of substance P (SP) to produce bronchoconstriction was investigated. In urethane-anaesthetized guinea pigs, intravenous injections of SP derivatives contracted differently bronchial smooth muscle and caused hypotension. The most effective bronchoconstrictor among SP analogs was the gamma-(glutamyl(5))Spd derivative of SP (Spd-SP; EC50 = 5.3 nmol/kg), which was more potent than the native peptide (EC50 = 26.5 nmol/kg). In contrast, the gamma-(glutamyl(5))Spm derivative of SP (Spm-SP) was found completely unable to cause bronchoconstriction and was significantly less effective than SP in determining hypotension. The contractile effect of Spd-SP and Spm-SP was investigated in vitro on rat isolated colon, a well-characterized preparation rich in NK2 receptors. In addition, Spd-SP was tested on the endothelium-denuded rabbit pulmonary artery (RPA) and the hamster isolated trachea (HT), both tissue preparations containing only a single functional receptor subtype (NK2A and NK2B, respectively). The results obtained showed that Spd-SP recognizes NK2 receptors occurring on rat isolated colon more effectively (EC50 = 11 nM) than the native peptide (EC50 = 45 nM), Conversely, Spm-SP evokes a contractile response less effective than that elicited by SP (EC50 = 312 nM). Furthermore, Spd-SP (0.1-10 mu g kg(-1)) produced a concentration-dependent contraction of both HT and RPA, exhibiting a potency respectively 12 and 30 times higher than SP in contracting HT and RPA. Our results indicate that the introduction of a pd moiety at the level of glutamine-5 of SP gives rise to an analog that possesses a different capability to recognize NK2 receptors than the parent neptide. Moreover, since Spd-SP seems to contract more effectively RPA than HT, we conclude that it preferentially recognizes the NK2A receptor subtype. (C) 1998 Elsevier Science Inc.