Facilitated Delivery of Endomorphins and Morphine into the CNS

摘要

Endomorphins, endogenous brain opiates with the highest affinity and specifity for the mu opiate receptor, potently produce analgesia. A rapid brain- to-blood efflux system could give misleading results when entry rates are determined. Preliminary results show that endomorphin-1 and endomorphin-2 are saturably transported from brain to blood, as shown by self-inhibition by an excess of that peptide. There also was cross-inhibition of each endomorphin by the other, indicating shared components for the efflux system. CGRP, substance P, or constriction of the sciatic nerve did not decrease efflux. Furthermore, chronic pain induced by sciatic nerve constriction caused a striking decrease in endomorphin-2 immunoreactivity on the nerve-injured side in the spinal cord.