Melatonin pretreatment improves liver function and hepatic perfusion after hemorrhagic shock

Area of Science:

• Physiology
• Pharmacology
• Hepatology

Background:

• Exogenous melatonin (MEL) administration shows antioxidative effects, attenuating organ damage in ischemia/reperfusion (I/R) and inflammation models.
• The specific organ-protective effects of MEL in hemorrhagic shock have not been previously investigated.

Purpose of the Study:

• To evaluate the role of MEL pretreatment in maintaining hepatic perfusion, redox state, and function following hemorrhagic shock and resuscitation.
• To investigate the involvement of MEL receptor activation in these protective effects.

Main Methods:

• Hemorrhagic shock model in rats (MAP 35 +/- 5 mmHg for 90 min) followed by 2 hours of reperfusion.
• Measurements included NADPH autofluorescence, hepatic microcirculation, hepatocellular injury via intravital microscopy, and plasma disappearance rate of indocyanine green (PDRICG) for liver function.
• Animals were pretreated with MEL (10 mg kg(-1), i.v.) or vehicle 15 min before hemorrhage; some received melatonin receptor antagonist luzindole (LZN).

Main Results:

• MEL pretreatment significantly improved PDRICG compared to controls (15.02% min(-1) vs. 6.18% min(-1), P = 0.001).
• Intravital microscopy showed improved hepatic perfusion index, redox state, and reduced hepatocellular injury in MEL-pretreated rats.
• The melatonin receptor antagonist luzindole (LZN) nearly abolished the protective effect of MEL on liver function (PDRICG: 7.31% min(-1)), while other protective effects were not influenced by LZN.

Conclusions:

• Melatonin pretreatment effectively maintains liver function after hemorrhagic shock through receptor-dependent pathways.
• While some protective effects may stem from antioxidative actions, liver function preservation is primarily mediated via receptor activation.
• This study highlights MEL as a potential therapeutic agent for managing liver injury associated with hemorrhagic shock.