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Selective protection of methionine enkephalin released from brain slices by enkephalinase inhibition
Abstract:
Methionine enkephalin release was evoked by depolarization of slices from rat striatum with potassium. In the presence of 0.1 microM thiorphan [(N(R,S)-3-mercapto-2-benzylpropionyl)glycine], a potent inhibitor of enkephalin dipeptidyl carboxypeptidase (enkephalinase), the recovery of the pentapeptide in the incubation medium was increased by about 100 percent. A similar effect was observed with the dipeptide phenylalanylalanine, a selective although less potent enkephalinase inhibitor. Inhibition of other known enkephalin-hydrolyzing enzymes--aminopeptidase by 0.1 mM puromycin or angiotensin-converting enzyme by 1 microM captopril--did not significantly enhance the recovery of released methionine enkephalin. These data indicate that enkephalinase is critically involved in the inactivation of the endogenous opioid peptide released from striatal neurons.
Insights
Enkephalinase inhibition significantly increased methionine enkephalin recovery in rat striatum. This suggests enkephalinase plays a key role in inactivating this endogenous opioid peptide.
Area of Science:
- Neuroscience
- Neurochemistry
- Pharmacology
Background:
- Methionine enkephalin is an endogenous opioid peptide involved in pain modulation and reward pathways.
- The striatum is a brain region rich in enkephalins and plays a role in motor control and reward.
- Understanding the regulation of endogenous opioid peptides is crucial for developing novel pain management strategies.
Purpose of the Study:
- To investigate the role of enkephalinase in the inactivation of methionine enkephalin released from rat striatal neurons.
- To determine if specific enkephalinase inhibitors can enhance the recovery of methionine enkephalin.
- To differentiate the role of enkephalinase from other peptidases in methionine enkephalin degradation.
Main Methods:
- Depolarization of rat striatal slices using potassium to evoke methionine enkephalin release.
- Incubation with specific inhibitors of enkephalinase (thiorphan, phenylalanylalanine).
- Incubation with inhibitors of other peptidases (puromycin for aminopeptidase, captopril for angiotensin-converting enzyme).
- Quantification of methionine enkephalin recovery in the incubation medium.
Main Results:
- Thiorphan, a potent enkephalinase inhibitor, increased methionine enkephalin recovery by approximately 100%.
- Phenylalanylalanine, a selective enkephalinase inhibitor, also enhanced methionine enkephalin recovery.
- Inhibition of aminopeptidase or angiotensin-converting enzyme did not significantly affect methionine enkephalin recovery.
- These findings highlight the specific role of enkephalinase in methionine enkephalin breakdown.
Conclusions:
- Enkephalinase is critically involved in the inactivation of endogenously released methionine enkephalin in the rat striatum.
- Targeting enkephalinase represents a potential therapeutic strategy for modulating endogenous opioid signaling.
- The results underscore the specificity of enkephalinase in regulating methionine enkephalin levels.