Opiate activity and receptor selectivity of dynorphin1-13 and related peptides

Experiments on the mouse vas deferens preparation obtained from animals chronically pretreated with selective opioid agonists have revealed the existence of opiate receptors with a high degree of preference for dynorphin1-13, alpha-neoendorphin1-8 and the eta-agonist MR 2034. Modification of the dynorphin sequence, by introduction of D-alanine into position 2, resulted in a complete loss of dynorphin-like agonistic activity on the tolerant mouse vas deferens. None of the dynorphin-related peptides tested displayed a pronounced opiate-like antinociception when administered intracerebroventricularly into rats.