EFFECT OF ENKEPHALIN AND ENKEPHALIN ANALOGS ON GUINEA-PIG ILEUM AND RAT-BRAIN OPIATE RECEPTOR

  • 1 January 1977
    • journal article
    • research article
    • Vol. 226  (1) , 69-80
Abstract
The 2 naturally occurring enkephalins (methionine-enkephalin and leucine-enkephalin) were synthesized as well as 4 other analogs (methionine-enkephaline amide, S-benzyl sulfonium analog of methionine-enkephaline, 3-benzyl-tyrosine analog of methionine-enkephalin and 3-benzyl-tyrosine analog of leucine-enkephalin) to study their relative potency and their inactivation by different tissues. Morphine-like activity of the peptides was determined by measuring their inhibitory effect in the guinea pig ileum and their interaction with the brain opiate receptor; the order of affinity of the 3 most active peptides (methionine-enkephalin amide > methionine-enkephalin > leucine-enkephalin) for the rat brain opiate receptor was the same in the guinea pig ileum. The rate of peptide inactivation was studied in the guinea pig ileum and in the rat brain membrane preparation. Methionine-enkephalin amide was relatively more resistant to the ileum peptidases than the other peptides but was destroyed at the same rate by brain membranes; this variation in inactivation of methionine-enkephalin amide probably indicates the presence of different peptidases in each tissue preparation.