Summary of in vitro results.

[a]The apparent permeability, Papp (cm/s), across Caco-2 cell monolayers. Analysis were done using LC/MS and each point is expressed as mean ± SEM.[b]The Kiμ values of 1, 2, 3 and 4 for the MOP receptor were obtained using competitive radioligand binding assay. Competitive displacement of the MOP selective radioligand, [3H]DAMGO, was determined from whole SH-SY5Y cells in the presence of DPDPE (1 µM). Binding affinity values (Kiμ) were determined using seven concentrations of each compound in the range 10 pM to 1 µM performed in three independent experiments, each in triplicate. Data expressed as mean ± SEM. Competitive binding curves are shown in Fig. 2.[c]The IC50 values (nM) were estimated from dose-response curves shown in Fig. 3. Inhibition of forskolin-stimulated cAMP formation was measured to determine the agonist activity of the compounds. Experiments were performed three independent times, each in triplicate.[d]These values are obtained from the same experiment. ND, not determined. Each value represents mean ± SEM. *p1 in the same experiment.