Abstract

In the guinea-pig ileum myenteric plexus-longitudinal muscle preparation, products from the dynorphin gene fell into three groups according to their potency. Dynorphin A was the most potent; dynorphin-32, dynorphin B, dynorphin B-29 and alpha-neo-endorphin were about equipotent and 10 to 20 times less potent than dynorphin A; dynorphin A-(1-8) and beta-neo-endorphin were about 200 times less potent than dynorphin A. Dynorphin A (a kappa agonist) was about 10 times less sensitive to antagonism by naloxone (as measured by naloxone Ke) than was normorphine (a mu agonist). Ke values for dynorphin-32, dynorphin B and alpha-neo-endorphin were the same as for dynorphin A, indicating that these peptides are also highly selective kappa agonists. Dynorphin A-(1-8), dynorphin B-29 and beta-neo-endorphin had Ke values intermediate between dynorphin A and normorphine, suggesting that they interact at both kappa and mu receptors. Addition of peptidase inhibitors to the bathing medium increased the potencies of dynorphin B, dynorphin B-29, alpha-neo-endorphin, dynorphin A-(1-8) and beta-neo-endorphin, but not of dynorphin A, dynorphin-32 or normorphine. The inhibitors did not change the naloxone Ke for dynorphin A or normorphine, or for dynorphin B-29, dynorphin A-(1-8) and beta-neo-endorphin, suggesting that the intermediate values were not caused by degradation to products with different receptor selectivities from the parent compounds. Ke for dynorphin-32, dynorphin B and alpha-neo-endorphin changed from being the same as dynorphin A in the absence of inhibitors to intermediate between dynorphin A and normorphine in the presence of inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)