Endogenous morphine and codeine: release by the chromaffin cells of the eel

Both the adrenomedullary equivalent and the plasma of the American eel (Anguilla rostrata) contain endogenous morphine and codeine. The opiate concentrations are similar to those found in the rat adrenal and human plasma, respectively. The adrenal medulla equivalent of the eel was perifused in vitro and the levels of catecholamines and endogenous opiate alkaloids in the perfusate were measured. A strong correlation between the release of morphine and codeine and between the release of norepinephrine (NE) and epinephrine (E) was found. On the other hand, there was no significant correlation between the release of dopamine (DA) and that of the other catecholamines or opiate alkaloids, suggesting three different ways of release of these components of the secretory cocktail of the chromaffin cells. The plasma of eels stressed by urethane anesthesia showed a substantial increase in DA, NE, and E levels but there was no clear stress response of plasma morphine and codeine.