Comparative effects of dynorphin A(1-9) pyrrolidine analogs on isolated tissues

Three dynorphin A(1-9) pyrrolidine analogs were synthesized by substituting isoleucine at position 8 with alanine (Ala), D-alanine (D-ala), and D-leucine (D-leu), and assayed for their effect on electrically induced twitches of the isolated guinea pig ileum and mouse vas deferens. All three dynorphin A(1-9) pyrrolidine analogs caused inhibition of the evoked twitches of the two preparations dose-dependently that was reversed by naloxone. However, the substitution by alanine or D-alanine resulted in a decrease in potency on guinea pig ileum when compared to dynorphin A(1-9) pyrrolidine and substitution by D-leucine caused a considerable loss of potency in both mouse vas deferens and guinea pig ileum. Although these substitutions reduced overall potency, a change of potency ratio towards more delta selectivity resulted.