Endomorphin 1 activates nitric oxide synthase 2 activity and downregulates nitric oxide synthase 2 mRNA expression

Area of Science:

• Immunology
• Neuroscience
• Pharmacology

Background:

• Endomorphins 1 and 2 are opioid peptides with high affinity for mu receptors.
• Opioid peptides can induce nitric oxide (NO) release from immune cells.
• Endomorphins may influence vasodilation through NO release.

Purpose of the Study:

• To investigate the effect of endomorphins 1 and 2 on nitric oxide release and nitric oxide synthase 2 (NOS 2) mRNA expression in J774 macrophages.
• To determine the involvement of NOS 2 and mu-opioid receptors in endomorphin-induced NO release.

Main Methods:

• J774 macrophages were stimulated with endomorphin 1 or 2.
• Nitric oxide release was measured using Griess assay and real-time amperometric detection.
• NOS 2 mRNA expression was assessed via RT-PCR.
• Specific inhibitors and antagonists (1400W, beta-funaltrexamine hydrochloride) were used.

Main Results:

• Endomorphin 1 (10^-6 M) stimulated rapid, transient NO release, peaking at 1000-1500s.
• Endomorphin 2 did not induce NO release at any tested concentration.
• The stimulatory effect of endomorphin 1 was inhibited by the NOS 2 inhibitor 1400W.
• NOS 2 mRNA expression was not upregulated by endomorphin 1 or lipopolysaccharide at 30 min.
• Endomorphin 1 treatment led to downregulation of NOS 2 mRNA expression, unlike lipopolysaccharide.
• A mu-opioid receptor antagonist blocked endomorphin 1-induced NO release.

Conclusions:

• Endomorphin 1 rapidly stimulates NO release from macrophages through NOS 2 activation.
• This effect is mediated by mu-opioid receptors.
• Endomorphin 1's action on NO release is distinct from lipopolysaccharide, particularly concerning NOS 2 transcription.