Melatonin pretreatment improves gastric mucosal blood flow and maintains intestinal barrier function during hemorrhagic shock in dogs

Melatonin improves hepatic perfusion after hemorrhagic shock and may reduce stress-induced gastric lesions. This study was designed to investigate whether pretreatment with melatonin may influence gastric mucosal microcirculatory perfusion (μflow), oxygenation (μHbO₂ ), or intestinal barrier function during physiological and hemorrhagic conditions in dogs.

In a randomized crossover study, five anesthetized foxhounds received melatonin 100 μg kg^-1 or vehicle (ethanol 5%) intravenously in the absence or presence of hemorrhagic shock (60 minutes, -20% blood volume). Systemic hemodynamic variables, gastric mucosal perfusion, and oxygenation were recorded continuously; intestinal barrier function was assessed intermittently via xylose absorption.

During hemorrhagic shock, melatonin significantly attenuated the decrease in μflow, compared with vehicle (-19±9 vs -43±10 aU, P<.05), without influence on μHbO₂ . A significant increase in xylose absorption was detected during hemorrhage in vehicle-treated dogs, compared with sham-operated animals (13±2 vs 8±1 relative amounts, P<.05); this was absent in melatonin-treated animals (6±1 relative amounts). Melatonin did not influence macrocirculation.

Melatonin improves regional blood flow suggesting improved oxygen delivery in gastric mucosa during hemorrhagic shock. This could provide a mechanism for the observed protection of intestinal barrier function in dogs.