Related Experiment Video
Updated: Aug 16, 2026
Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities
Published on: July 29, 2014
Met-enkephalin involvement in morphine-modulated peritonitis in swiss mice
Magdalena Chadzinska1, Anna Scislowska-Czarnecka, Krystyna Pierzchala-Koziec
1Department of Evolutionary Immunobiology, Jagiellonian University, Kraków, Poland. chadz@zuk.iz.uj.edu.pl
Abstract:
Morphine coinjection with zymosan inhibits pain and leukocyte accumulation during peritonitis in several strains of mice, and affects systems of endogenous opioids. Present investigations focus on Met-enkephalin (Met-ENK) in the inflamed peritoneal cavity and brain centers of Swiss mice. Males of Swiss mice were IP injected with zymosan or zymosan supplemented with morphine. At the selected time points the peritoneal leukocytes were counted and the Met-ENK level was measured in exudatory fluid and leukocytes, striatum, hypothalamus, and pituitary gland. The Met-ENK content in peritoneal fluid rised sharply after zymosan injection, which corresponded with its decline in exudatory leukocytes, hypothalamus, and striatum. Morphine coinjection enhanced intraperitoneal accumulation of Met-ENK and its release from exudatory leukocytes, but inhibited its early fluctuations in hypothalamus and striatum. Effects of morphine-modulated inflammation on the Met-ENK system lasted longer than 7 days.
Insights
Morphine co-administration with zymosan impacts Met-enkephalin (Met-ENK) levels during peritonitis. Coinjection with morphine enhanced Met-ENK in the peritoneal cavity while stabilizing brain levels, with effects lasting over seven days.
Area of Science:
- Neuroscience
- Immunology
- Pharmacology
Background:
- Zymosan-induced peritonitis in mice involves endogenous opioid systems.
- Morphine's effects on pain and leukocyte accumulation are known.
- Met-enkephalin (Met-ENK) is a key endogenous opioid peptide.
Purpose of the Study:
- To investigate the impact of morphine and zymosan on Met-ENK levels.
- To examine Met-ENK distribution in peritoneal fluid, leukocytes, and brain regions.
- To understand the temporal effects of morphine on Met-ENK during inflammation.
Main Methods:
- Swiss mice were injected with zymosan or zymosan plus morphine.
- Leukocyte counts in peritoneal fluid were performed.
- Met-ENK levels were measured in peritoneal fluid, leukocytes, striatum, hypothalamus, and pituitary gland.
Main Results:
- Zymosan injection increased peritoneal fluid Met-ENK, decreasing it in leukocytes and brain regions.
- Morphine coinjection boosted peritoneal Met-ENK accumulation and release from leukocytes.
- Morphine inhibited early Met-ENK fluctuations in the hypothalamus and striatum.
Conclusions:
- Morphine modulates Met-ENK dynamics during zymosan-induced peritonitis.
- Coinjection with morphine alters Met-ENK distribution between the periphery and central nervous system.
- The observed effects on the Met-ENK system persist for over seven days.
