Royal Academy of Medicine in Ireland Section of Biological Sciences Proceedings of Summer Meeting Held at University of Ulster at Jordanstown, 22nd & 23rd June, 1990

243,901), but an understanding of its role in control of airway function in health and disease has been difficult because of the lack of specific antagonists.It was the purpose of this study to synthetise analogues of NKA and to test them for pharmacological antagonism of NKA-induced contraction of guinea-pig tracheal smooth muscle.We have previously reported that NKA analogue in which glycine 8 was replaced by aminoisobutyric acid (Aib) is an antagonist of NKA, but not Substance P, activity on tracheal smooth muscle from guinea-pig (Abu Shanab et al, Biochem.Soc.Trans.1990: 18, 286).We now report the effect on biological activity of deletions at the N-terminus.NKA was purchased from Biosyn Ltd. (Belfast, N. Ireland) and the peptides [Ala s, Aib s, Leu 1~ NKA (4-10), [Ala ~, Aib 8, Leu 1~ NKA (2-10) and [Ala s, Aib s, Leu 1~ NkA, hereafter referred to as peptides 1, 2 and 3 respectively, were synthetised by solid phase methods.Isometric contraction of isolated guinea-pig tracheal rings in response to exogenous NKA (10 -1~ to lO-6M) was recorded as described previously (Abu Shanab et al, Biochem.Soc.Trans.1990: 18, 286) and the effect of the peptide analogues on the NKA doseresponse relationship examined.In the presence of peptide 3 (10 -8 to 10-6M) NKA evoked contractions were reduced at all doses producing acharacteristic shift in the NKA dose-response curve suggestive of classical non-competitive antagonism, although contractions to substance P (SP; 10 -8 to 10-6M) were unaltered by analogue.In contrast, peptide 2 (104 to 1 ff6M) caused a dose-dependent shift to the right of the NKA doseresponse curve with no depression of the maximum NKA response.Peptide 2 showed no pharmaclogical antagonism to SP.A schild regression plot for peptide 2 antagonism of NKA evoked contractions yielded a straight line of slope -0.4 with an interscept (PA2) of 7.7 on the abscissa.Unlike peptides 2 and 3, peptide 1 (10-6M) itself caused contraction of the tracheal preparation.In conclusion, peptide analogues that selectively antagonise the activity of NKA on tracheal smooth muscle have been produced by replacement of Gly s in a NKA ,,~icgue that also had the substitutions Ala s and Leu 1~ Removal G~ the N-terminal residue did not abolish this selectivity although the nature of the antagonism was altered.Removal of a further two amino acid residues from the Nterminus resulted in the generation of agonist activity.