Micturition in naive and morphine-dependent rats.

Area of Science:

• Pharmacology
• Urology
• Neuroscience

Background:

• Opioid analgesics like morphine are widely used for pain management.
• The effects of morphine on the urinary system, particularly micturition, are not fully understood.
• Understanding morphine's impact on voiding is crucial for managing patient side effects.

Purpose of the Study:

• To investigate the effects of morphine sulfate and morphine base on the micturition volume threshold in conscious rats.
• To assess the development of tolerance to morphine's effects on micturition.
• To examine the role of morphine in the withdrawal syndrome related to micturition.

Main Methods:

• Conscious, water-loaded rats were used to record voiding responses.
• Morphine sulfate (5 mg/kg) was administered, and micturition volume threshold (MV) was measured.
• Morphine base pellets (150 or 300 mg) were implanted for 12 days to assess chronic effects and tolerance.
• Naloxone was used to precipitate withdrawal symptoms.

Main Results:

• Morphine sulfate administration increased the mean MV by 40%.
• Implanted morphine pellets significantly elevated MV for up to 10 days, approximately doubling it compared to controls.
• Complete bladder emptying occurred, and tolerance to antinociceptive effects developed within 3 days, while tolerance to micturition effects was minimal.
• Pellet removal led to reduced MV, and naloxone-induced withdrawal significantly decreased MV.

Conclusions:

• Morphine significantly elevates the volume threshold for micturition in rats.
• Tolerance to morphine's effects on micturition develops slowly compared to its analgesic effects.
• Alterations in micturition volume threshold are a component of morphine withdrawal syndrome.