Further proctolin analogues modified in the position 2 of the peptide chain and their myotropic effects in insects Tenebrio molitor and Schistocerca gregaria
We have extended our studies on the structure-activity relationship in neuropeptide proctolin (Arg-Tyr-Leu-Pro-Thr) by evaluating the effects of a series of proctolin analogues modified in position 2 of the peptide chain, including: [Phe(p-Cl)2]-(1), [D-Phe(p-Cl)2]-(2), [N-Me-Tyr2]-(3), [D-Phe(p-NH2)2]-(4), [D-Phe(p-N,N-di-Me)2]-(5), [N-Me-Tyr(OMe)]-(6), [D-3-Pal2]-(7), [L-Nal2]-(8), [D-Nal2]-(9), [Lys(Nic)2]-(10), [D-Lys(Nic)2]-(11), [D-Phe-(p-NO2)2]-(12). These peptides were evaluated for myotropic activity on the heart of Tenebrio molitor and contractile activity of the foregut of Schistocerca gregaria. Analogues 1-5, 7-9, and 12 retained a weak cardiotropic activity in Tenebrio molitor while peptides 1, 8 and 12 preserved 15-25% of the locust-gut contracting activity of proctolin. Peptides 2, 4 and 7 showed weak inhibitory activity in Schistocerca gregaria foregut, whereas only peptides 2, 4 and 7 reduced the maximum response to appllied proctolin by 64% and 49% respectively, at the 10-6 M concentration.</p
