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Effects of temperature on the interaction of morphine with opioid receptors
Abstract:
The electrically stimulated guinea pig ileum preparation was used to determine the effects of temperature on the affinity of morphine for opioid receptors. The potency of morphine (expressed as the concentration which produces 50% inhibition--IC50) was significantly decreased at 30 degrees C (IC50 41.0 x 10(-8) mol litre-1) and increased at 40 degrees C (IC50 5.1 x 10(-8) mol litre-1) when compared with its potency at 37 degrees C (IC50 8.8 x 10(-8) mol litre-1). Experiments carried out in the presence of naloxone (a competitive opioid antagonist) indicated that the affinity of opioid receptors for this antagonist was not affected by temperature. Further studies using B-funaltrexamine (a mu-specific, non-reversible opioid antagonist) revealed an increase in morphine receptor affinity when temperature was increased from 30 to 37 degrees C. The data demonstrated that the potency of morphine increased with temperature; the affinity of naloxone for opioid receptors was unaltered by temperature; and the affinity of morphine for mu-receptors reached an optimal value within the range 30-37 degrees C.
Insights
Temperature significantly impacts morphine
Area of Science:
- Pharmacology
- Physiology
- Biochemistry
Background:
- Opioid receptors are crucial targets for pain management.
- Understanding how physical factors like temperature affect drug-receptor interactions is vital for optimizing therapeutic efficacy.
- Previous research has not fully elucidated the temperature-dependent affinity of morphine for opioid receptors.
Purpose of the Study:
- To investigate the influence of varying temperatures on the affinity of morphine for opioid receptors.
- To determine the effect of temperature on the potency of morphine and its interaction with specific opioid receptor subtypes.
- To assess the temperature-dependent binding characteristics of opioid antagonists like naloxone and b-funaltrexamine.
Main Methods:
- Utilized an electrically stimulated guinea pig ileum preparation.
- Measured the potency of morphine by determining the concentration required for 50% inhibition (IC50) at different temperatures (30°C, 37°C, 40°C).
- Investigated the effects of temperature on opioid receptor affinity using naloxone and b-funaltrexamine (a mu-specific antagonist).
Main Results:
- Morphine potency (IC50) was significantly altered by temperature, decreasing at 30°C and increasing at 40°C relative to 37°C.
- The affinity of opioid receptors for naloxone remained unaffected by temperature changes.
- Affinity of morphine for mu-receptors increased as temperature rose from 30°C to 37°C, suggesting an optimal binding range.
Conclusions:
- Morphine's potency at opioid receptors is temperature-dependent, with increased potency observed at higher temperatures within the tested range.
- Temperature does not influence the binding affinity of naloxone to opioid receptors.
- The affinity of morphine for mu-opioid receptors exhibits an optimal range between 30°C and 37°C, highlighting the importance of temperature in opioid pharmacology.