KINETIC-PARAMETERS OF ANTAGONISM BY THE DELTA-OPIOID RECEPTOR-SELECTIVE PEPTIDE ANTAGONIST BOC-TYR-PRO-GLY-PHE-LEU-THR AGAINST SELECTIVE AND NONSELECTIVE AGONISTS IN THE MOUSE VAS-DEFERENS

The kinetic parameters of antagonism by the delta opioid receptor sele ctive antagonist N-t-Boc-Tyr-Pro-Gly-Phe-Leu-Thr, obtained by using mo derately selective or selective agonists, were compared in the mouse v as deferens bioassay. The apparent affinity for the preferred receptor type was 6.8 times higher when selective agonist was used, resulting in a K(e) of 81.4 nM (66.3-99.9, n = 6) against [D-Ala2, D-Leu5]-enkep halin, with a 3700-fold delta over mu or kappa selectivity ratio.