In vitro pharmacology of the opioid peptides, enkephalins and endorphins.
In the guinea-pig ileum methionine-enkephalin, normorphine and morphine are equipotent in depressing electrically evoked contractions; leucine-enkephalin has about 25% of the activity. The mouse vas deferens is more sensitive to the enkephalins which are 30 to 60 times more potent than morphine. Fragments of beta-lipotropin61-91 (beta-endorphin) having sequences up to LPH76 are more potent in the mouse vas deferens than in the guinea-pig ileum but beta-endorphin is about equipotent in the two preparations. None of the peptides has antagonist activity. Methionine-enkephalin and normorphine are equipotent in inhibiting [3H]-naloxone binding by homogenate of guinea-pig brain in the absence of Na+ while leucine-enkephalin has only 25% of this activity. In the guinea-pig ileum, naloxone antagonises normorhine and the enkephalins equally well whereas in the mouse vas deferens about ten times more naloxone is required for the enkophalins that for normorphine. Methionine-enkephalin depresses output of acetylcholine in the guinea-pig ileum and of noradrenaline in the mouse vas deferens.
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D003864:Depression, Chemical; D004558:Electric Stimulation; D004723:Endorphins / Q000494:pharmacology*; D004745:Enkephalins / Q000494:pharmacology*; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects; D009270:Naloxone / Q000378:metabolism / Q000494:pharmacology; D018377:Neurotransmitter Agents / Q000378:metabolism; D009842:Oligopeptides / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology*; D009435:Synaptic Transmission / Q000187:drug effects; D013997:Time Factors; D014649:Vas Deferens / Q000187:drug effects / Q000378:metabolism; D008083:beta-Lipotropin / Q000494:pharmacology
D004723:Endorphins; D004745:Enkephalins; D018377:Neurotransmitter Agents; D009842:Oligopeptides; D010446:Peptide Fragments; D010455:Peptides; D009270:Naloxone; D008083:beta-Lipotropin