Humoral endorphin: A new endogenous factor with opiate-like activity

Y. Sarne*, B. A. Weissman, O. Keren, G. Urca

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Humoral (H) endorphin, a novel endogenous opioid ligand detected in brain, blood and cerebrospinal fluid was tested in a series of opiate sensitive assays. H-endorphin displaced radiolabeled enkephalin from its specific bindings sites and inhibited the electrically evoked contraction of the guinea pig ileum and mouse vas deferens. When injected to unanesthesized animals, humoral endorphin induced analgesia in rats and mydriasis in mice. The activity of H-endorphin both in vitro and in vivo attests to its opioid nature. However, while its antinociceptive effect was blocked by naloxone, mydriasis induced by H-endorphin was resistant to the effect of the opiate antagonist. Similarly, intermediate concentrations of naloxone inhibited the effect of H-endorphin on the guinea pig ileum while its effect on the mouse vas deferens was completely refractory to naloxone. The physiological function of humoral endorphin in various naturally occuring states that show similar paradoxical interactions with naloxone is discussed.

Original languageEnglish
Pages (from-to)673-680
Number of pages8
JournalLife Sciences
Issue number6
StatePublished - 9 Feb 1981


FundersFunder number
Charles Smith Foundation17/79
Israel Center for Psychobiology


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