Paralytic activity of (des-Glu1)conotoxin GI analogs in the mouse diaphragm.

A series of 20 peptide analogs of (des-Glu1)conotoxin GI were prepared by solid phase synthesis. The peptides were tested for their abilities to inhibit contractions in the mouse-diaphragm-with-phrenic-nerve assay. (Des-Glu1)conotoxin has an IC50 of 2.7 x 10(-7) M in this assay. Results from this assay show that total loss of paralytic activity occurs when Pro is replaced by Gly, Tyr by D-Tyr, or Gly by D-Phe. In most cases loss or change in length of one of the disulfide rings eliminates paralytic activity except with compound 17, which is weakly active, IC50 = 7.0 x 10(-5) M. Replacement of the Cys1-Cys6 disulfide bond with an amide bond (compound 9) greatly lowers paralytic activity, IC50 = 3.7 x 10(-5) M.

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.

Opioid-like properties of seven dynorphin (1-10) analogs.

In order to disassociate the k action of dynorphin from its other actions, seven analogs were synthesized and evaluated for pharmacologic activity in comparison with dynorphin (1-13) and dynorphin amide (1-10). Dynorphin (1-10) was modified by protecting the terminal carboxy group, incorporating thioproline at position 10 and substituting methionine for leucine at position 5. All analogs exhibited the ability to inhibit electrically-induced twitches of the guinea pig ileum and mouse vas deferens in a manner that was dose dependent and naloxone reversible. The decapeptide terminating with a pyrrolidine group showed the highest potency in the ilea and mouse vas deferens. None of the analogs showed analgetic activity by the mouse tail flick test. Binding studies using mouse brain synaptosomes showed that all seven analogs can displace the binding of tritiated dihydromorphine (DHM), ethylketocyclazocine (EKC) and D-Ala-D-Leucine enkephalin (DADL). The alterations in chemical structure affected affinity of the analogs to the opiate receptor and their pharmacologic properties differently, suggesting that different opiate subtypes may be involved.