The effects of endorphins on mucous glycoprotein secretion from feline airways in vitro

The effect of opioid peptide hormones on respiratory glycoprotein secretion was investigated in a cat tracheal organ culture system. Dynorphin A (dyn, 10(-5) M), alpha-endorphin (alpha E, 10(-5) M) and morphine sulfate (MS, 10(-4) M) stimulated mucous glycoprotein (MGP) release from airways, whereas all other endorphins tested failed to have such an effect. Dyn did so in a dose dependent manner (10(-5)-10(-7) M) with a peak effect after a one hour incubation. Two sets of data suggest that dyn is acting through the previously described endorphin-kappa receptor: The active binding site of dyn is at the carboxyl end of the peptide; dyn fragment 1-13 stimulated MGP secretion while dyn fragment 1-8 did not. Naloxone in equimolar concentration totally inhibited the dyn response. We, therefore, conclude that the endorphins dyn and alpha E stimulate MGP release and that dyn is probably acting by stimulating kappa receptors.