Kinetic parameters of antagonism by the delta opioid receptor selective peptide antagonist Boc-Tyr-Pro-Gly-Phe-Leu-Thr against selective and non-selective agonists in the mouse vas deferens.

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