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Augmenting effect of opioids on nitrite production by stimulated murine macrophages
1Department of Clinical Pharmacology, Silesian University School of Medicine, Katowice, Poland.
Abstract:
The effects of methionine-enkephalin and the selective agonists of mu-, delta- and kappa-opioid receptor subtypes [D-Ala2,N-Me-Phe4,Gly5-ol]enkephalin, [D-Pen(2,5)]enkephalin U-50488 on the production of nitrite by activated peritoneal murine macrophages were studied. Macrophages were activated with interferon-gamma plus lipopolysaccharide in the presence or absence of graded concentrations of opioids. Methionine-enkephalin and mu-; delta- and kappa-agonists combined with interferon-gamma plus lipopolysaccharide caused an increase in nitrite release from cultured macrophages. Only 10 mM U-50488 led to a decrease in nitrite release from interferon-gamma and LPS-stimulated macrophages. This effect was not produced in a naloxone-sensitive manner. The opioids added to the fresh culture 8 h after the stimulation of macrophages by interferon-gamma plus lipopolysaccharide--when an inducible form of nitric oxide synthase activity is presumably expressed--did not alter the rate of nitrite production. This suggests that the effect of opioids on nitric oxide synthase is produced at the transcriptional level. The opioid receptor antagonist naloxone reduced the stimulatory effect of opioids on nitrite production by stimulated macrophages. Opioids added to the culture of resting macrophages did not change nitrite release from macrophages which were later induced with interferon-gamma plus lipopolysaccharide. The results of this study suggest that methionine-enkephalin can modulate the immune response by controlling, via opioid receptors, the production of nitric oxide.
Insights
Methionine-enkephalin and opioid receptor agonists can increase nitrite production in activated macrophages. This immune modulation by methionine-enkephalin occurs via opioid receptors, affecting nitric oxide production.
Area of Science:
- Immunology
- Neuroscience
- Pharmacology
Background:
- Opioid receptors are involved in modulating immune responses.
- Nitric oxide (NO) production by macrophages plays a crucial role in immunity.
- The influence of specific opioid receptor subtypes on NO production is not fully understood.
Purpose of the Study:
- To investigate the effects of methionine-enkephalin and selective mu-, delta-, and kappa-opioid receptor agonists on nitrite production by activated murine macrophages.
- To determine if these opioid effects on NO production are mediated through opioid receptors.
Main Methods:
- Murine peritoneal macrophages were activated using interferon-gamma and lipopolysaccharide (LPS).
- Opioids (methionine-enkephalin, mu-, delta-, and kappa-agonists) were added at various concentrations to activated macrophages.
- Nitrite release was measured as an indicator of NO production.
- The role of opioid receptors was assessed using the antagonist naloxone.
Main Results:
- Methionine-enkephalin and mu-, delta-, and kappa-opioid agonists increased nitrite release from activated macrophages.
- A specific kappa-agonist (U-50488) at 10 mM decreased nitrite release, an effect not sensitive to naloxone.
- Opioids added later in the culture (8h post-stimulation) did not affect nitrite production, suggesting transcriptional regulation.
- Naloxone partially blocked the stimulatory effect of opioids on nitrite production.
Conclusions:
- Methionine-enkephalin can modulate the immune response by influencing nitric oxide production in macrophages via opioid receptors.
- Opioid receptor activation generally enhances NO production, but specific receptor subtypes may have differential effects.
- The effects of opioids on NO production appear to be regulated at the transcriptional level.