OPIATE MODULATION OF DYNORPHIN CONVERSION IN PRIMARY CULTURES OF RAT CEREBRAL-CORTEX

Rat brain cortical cells in primary culture were used to investigate l ong-term effects of opiates on endopeptidases acting on dynorphin pept ides. Enzyme activity in the soluble fraction of the cells converted d ynorphin B to Leu-enkephalin-Arg(6) and to a lesser extent to Leu-enke phalin. Five day treatment with 10 mu M morphine increased the convers ion to Leu-enkephalin-Arg(6) by 370%. This effect was prevented by the presence of naloxone in the culture medium. The opiate-inducible acti vity was directed to the Arg-Arg bond in dynorphins with preference fo r dynorphin B > alpha-neoendorphin > > dynorphin A. The K-m for the ge neration of Leu-enkephalin-Arg(6) from dynorphin B was 40 mu M. Enzyme activity was inhibited by dynorphin fragments, in the following order of potency: dynorphin A(1-13) > A(2-13)> > A(1-17) > A(2-17) and by S H-reagents, suggesting the presence of a cysteine-protease. The opiate -stimulated dynorphin-converting enzyme (DCE)-activity affects the bal ance between dynorphin peptides (selective for kappa-opioid receptors) and enkephalin peptides (selective for delta-opioid receptors). Since both types of opioid peptides can influence the development of opiate tolerance, the change in the extent of this transformation may be fun ctionally important.