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

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Intraventricular injection of morphine sulfate, 40 μg, 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.