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The effect of morphine pretreatment on hypothermia induced by morphine in mice
Abstract:
Morphine caused an apparently dose-dependent hypothermia in mice. Co-administration of naloxone antagonised this effect. Pretreatment with a single dose of morphine induced detectable tolerance to the hypothermic effect of a second dose of morphine given 3 h later and naloxone was more effective in antagonising the hypothermic effect of morphine in morphine-pretreated mice than in saline-pretreated animals. The present study has shown that morphine pretreatment can augment the antagonistic effect of naloxone towards the hypothermic action of morphine.
Insights
Morphine causes dose-dependent hypothermia in mice, which is blocked by naloxone. Morphine pretreatment enhances naloxone's ability to counteract morphine-induced hypothermia, indicating tolerance development.
Area of Science:
- Pharmacology
- Neuroscience
- Physiology
Background:
- Opioids like morphine can induce hypothermia.
- Naloxone is a known opioid antagonist.
- Tolerance to opioid effects can develop with repeated administration.
Purpose of the Study:
- To investigate the effect of morphine pretreatment on morphine-induced hypothermia in mice.
- To examine the role of naloxone in antagonizing morphine-induced hypothermia after morphine pretreatment.
- To explore the development of tolerance to the hypothermic effects of morphine.
Main Methods:
- Administering varying doses of morphine to mice to observe hypothermic effects.
- Co-administering naloxone with morphine to assess its antagonistic properties.
- Pretreating mice with a single dose of morphine before a second morphine challenge 3 hours later.
- Comparing the effects of naloxone in morphine-pretreated versus saline-pretreated mice.
Main Results:
- Morphine induced a dose-dependent decrease in body temperature (hypothermia) in mice.
- Naloxone effectively antagonized the hypothermic effect of morphine.
- Pretreatment with morphine led to tolerance to the hypothermic effect of a subsequent morphine dose.
- Naloxone demonstrated enhanced efficacy in antagonizing morphine's hypothermic action in morphine-pretreated mice compared to saline-pretreated controls.
Conclusions:
- Morphine administration causes dose-dependent hypothermia in mice, modulated by naloxone.
- Evidence of tolerance to morphine-induced hypothermia was observed after a single pretreatment dose.
- Morphine pretreatment potentiates the antagonistic effect of naloxone on morphine-induced hypothermia, suggesting complex interactions in opioid receptor systems.