Delta and kappa opioid receptors in the rabbit ear artery

Delta and kappa opioid receptors have been characterized in the central ear artery of the rabbit. The delta selective D-Pen2,D-Pen5-enkephalin and the highly selective delta antagonist ICI 174864 have been used for the delta opioid receptors. Ke values were determined and compared to that of the electrically stimulated mouse vas deferens preparation. In case of kappa opioid receptors, Dynorphin (1-13) and Ethylketazocine were used as agonists and Mr 2266 as kappa antagonist. Because of the relatively low selectivity of the kappa antagonist (it is only twice as active at the kappa than at the mu receptor sites) the Ke values obtained in the rabbit ear artery were compared to both the normal and beta-funaltrexamine treated vasa deferentia. In the rabbit ear artery, the Ke values of Mr 2266 were also determined in the presence of the delta selective antagonist ICI 174864. The Ke values for the delta receptors were close in the two assay systems, suggesting that the delta receptors have similar properties in rabbit ear artery and mouse vas deferens. As for the kappa receptors, the Ke values in the rabbit ear artery were not significantly different in the presence or absence of the delta antagonist compound, nor were they different from the Ke values obtained on the normal mouse vas deferens. However, they were significantly different from that of the beta-funaltrexamine treated mouse vas deferens. Further experiments need to be done to interpret the meaning of these results.