INTERACTION OF HEMORPHINS WITH OPIOID RECEPTORS IN THE RAT VAS-DEFERENS AND GUINEA-PIG ILEUM

Hemorphins are endogenous opioid peptides which can be released by enz ymatic degradation of hemoglobin. A nonapeptide, LVV-hemorphin-6, has recently been isolated from human pituitaries and its primary structur e was found to be identical to fragment 32-40 of the beta-, gamma-, de lta- and epsilon-chain of human hemoglobin. In this study, LVV-hemorph in-6 and its shorter fragment hemorphin-6 (hemoglobin fragment 35-40) were tested for their effects on the electrically induced contractions in the rat vas deferens (RVD) and guinea-pig ileum (GPI) assays. The hemorphins showed weak inhibitory effects on the contractions in the R VD and both peptides significantly decreased the inhibitory action of beta-endorphin. The K-e-values were calculated to be 37 and 73 mu M fo r hemorphin-6 and LVV-hemorphin-6, respectively. In the GPI assay, bot h hemorphins induced opioid agonist-like effects. At high concentratio ns (100 mu M), hemorphin-6 antagonized the inhibitory action of normor phine, but not that of dynorphin A. These results indicate that the he morphins, already known as opioid agonists, can also act as opioid ant agonists in the RVD and GPI.