Release of a dynorphin A (1-8) degrading enzyme from the spinal cord by intraventricular morphine in the rat

Intraventricular injection of morphine sulfate, 40 micrograms, released an enzyme from the spinal cord into the perfusate which degraded dynorphin A (1-8) and, to a lesser extent, dynorphin A (1-13) in urethane anesthetized rats. The enzyme did not degrade dynorphin A (1-17), Met-enkephalin, Leu-enkephalin, substance P and neurotensin. This dynorphin A (1-8) degrading enzyme was inhibited by aprotinin, thiorphan, and, to a lesser extent, by bacitracin but was not inhibited by bestatin. A kinetic study of the interaction between dynorphin A (1-8) and aprotinin with the enzyme indicated that it is competitive in nature. The pharmacological significance of the findings is still unknown.