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Increased brain P-glycoprotein in morphine tolerant rats
C L Aquilante1, S P Letrent, G M Pollack
1Division of Drug Delivery and Disposition, School of Pharmacy, University of North Carolina, Chapel Hill 27599-7360, USA.
Life Sciences
|February 9, 2000
Summary
Chronic morphine exposure increases P-glycoprotein (a protein that affects drug transport) in rat brains. This P-glycoprotein induction may contribute to the development of morphine tolerance by reducing the drug
Area of Science:
- Neuroscience
- Pharmacology
- Molecular Biology
Background:
- Opioid analgesics like morphine are widely used for pain management.
- Development of tolerance to morphine can limit its long-term efficacy.
- P-glycoprotein, an efflux transporter, plays a role in drug disposition within the central nervous system.
Purpose of the Study:
- To investigate the effect of chronic morphine administration on P-glycoprotein expression in the rat brain.
- To explore the potential link between P-glycoprotein induction and the development of morphine tolerance.
Main Methods:
- Male Sprague-Dawley rats were administered morphine, saline, or dexamethasone daily for five days.
- Antinociceptive responses were assessed on day six to measure functional tolerance.
- Brain P-glycoprotein levels were quantified using Western blot analysis.
Main Results:
- Both morphine and dexamethasone treatments led to a reduced antinociceptive response compared to saline controls.
- Western blot analysis revealed approximately a twofold increase in brain P-glycoprotein in morphine-treated rats versus controls.
- Chronic morphine exposure significantly elevated P-glycoprotein levels in the rat brain.
Conclusions:
- Chronic morphine exposure induces P-glycoprotein expression in the rat brain.
- Increased P-glycoprotein may facilitate morphine efflux from the brain, thereby decreasing its pharmacological activity.
- P-glycoprotein induction represents a potential mechanism underlying the development of morphine tolerance.