COMPARISON OF THE MYOTROPIC ACTIVITY OF POSITION-2 MODIFIED ANALOGS OF PROCTOLIN ON THE HINDGUT OF PERIPLANETA-AMERICANA AND THE OVIDUCT OFLOCUSTA-MIGRATORIA

The largest series of position-2 modified proctolin analogues to have been examined to date were tested for their ability to mimic the basal contraction induced by proctolin on hindgut of the cockroach, Peripla neta americana, and oviduct of the locust, Locusta migratoria, Twelve analogues of proctolin (Arg-Tyr-Leu-Pro-Thr), differing in the substit uent (H, OMe, Oft, OPr, F, Cl, Br, I, NO2, NH2, N-3, Me) located at th e para-position of the aromatic amino acid, caused dose-dependent cont ractions of both tissues at concentrations quite similar to proctolin, Seven showed greater or equal potency on the hindgut but, with one ex ception, they were less active on the oviduct than proctolin, The rank order of potency of the analogues depends on the tissue, lending more support to the notion that insects have more than one type of proctol in receptor, No relationship was observed between myoactivity and lipo philic, steric, electron donating or electron withdrawing properties o f the-substituents at the para-position of the aromatic amino acid, Th is may be the result of more than one sub-type of proctolin receptor o n the specific tissue with differing structural requirements for optim um activity. Published by Elsevier Science Ltd.