The Effects And Mechanisms Of Different Resuscitation Fluids On Intestinal Injury Of Secondary Intra-abdominal Hypertension In Rats

Background:Intra-abdominal pressure(IAP)is the steady-state pressure concealed within the abdominal cavity,which is approximately 5–7 mm Hg in critically ill adults.When a sustained or repeated pathological elevation in IAP ? 12 mm Hg,intra-abdominal hypertension(IAH)is defined.Secondary IAH refers to conditions that do not originate from the abdominopelvic region,which is commonly encountered as a result of extra-abdominal injuries such as sepsis,capillary leak,major burns,trauma,or disease requiring massive fluid resuscitation.These states can present with a similar picture of systemic hypoperfusion and hypoxemia followed by subsequent resuscitation,which commonly result in a systemic ischemia/reperfusion injury with the hallmark of generalized edema or “third-spacing” of fluid.The same pathological process occurs in the intestine,and then results in secondary IAH.Secondary IAH has consistently been associated with significant organ failure,morbidity and mortality among critically ill adults.However,it remains uncertain as to how to prevent this condition in the very beginning to improve patient outcomes.Melatonin,a circadian hormone mainly secreted by the pineal gland,was initially identified in circadian regulation of physiological and neuroendocrine function.Subsequent studies demonstrated that melatonin and its metabolic derivatives have the charactor of strong free radical scavenging properties.In the recent years,a variety of anti-inflammatory effects have been observed when melatonin is applied exogenously under both in vivo and in vitro conditions.Since intestinal edema and capillary leak induced by inflammatory responses are cornerstones of secondary IAH,exogenous melatonin may prevent or slow the progression of secondary IAH by anti-inflammatory means in the intestine.This study was to build a rat model of secondary IAH that was induced by lactated Ringer's Solution(LR)resuscitation after trauma-hemorrhagic shock,and to study the effect of different fluids on secondary IAH through this model.We hypothesized that melatonin administration may prevent secondary IAH and ameliorate the intestinal injury.Methods:1.Building secondary IAH model in ratsAfter anaesthesia,Sprague–Dawley rats were arranged to generate portal hypertension,hemorrhage to a MAP of 40 mm Hg for 2 hrs and utilize an abdominal restraint device.After the above procedures,LR was followed at a rate of 30 ml/h for 6h.Mean arterial pressure(MAP),inferior vena cava pressure(IVCP),and urine output were recorded during the experiment.Western blot,immunohistochemistry and electron microscope were used to test protein expression and distribution of tight junction proteins.2.Comparation of different fluids resusucitation on secondary IAHThis study was to examine the effect of melatonin,7.5% hypertonic saline(HS),and hydroxyethyl starch 130/0.4(HES)in rats model of secondary IAH.We hypothesized that these treatment would attenuate the intestinal injury during the resuscitation and prevent the secondary IAH,and melatonin may have a superior effect.3.Effect of melatonin on secondary IAH in rats and its mechanismThe pathogenesis of intestinal mucosal barrier function injury in secondary IAH remains unclear.However,several signaling pathways have been explored to mediate the pathological processes,such as MAPKs,STATs and NF-?B.We used western blot to filtrate the key molecules involved in the regulation of protecting effect of melatonin in intestinal injury.Results:1.A rat model of secondary IAH was successfully built.A rat model of secondary IAH was successfully established by LR resuscitation after a combination of generating portal hypertension,hemorrhaging to a MAP of 40 mm Hg for 2 hrs and utilizing an abdominal restraint device.LR resuscitation after trauma-hemorrhage significantly worsened intestinal inflammatory markers,disrupted tight junctions,worsened the intestinal permeability and finally led to secondary IAH.2.Melatonin had a superior effect on intestinal injury in the development of secondary IAH.Compared with LR group,HS group and HES group,melatonin group were associated with higher MAP,lowered IVCP,less inflammatory and oxidative injury,less intestinal permeability,lowered incidence of secondary IAH.3.Melatonin prevented secondary intra-abdominal hypertension in rats possibly through inhibition of the p38 MAPK pathway.Exogenous administration of melatonin successfully attenuated the insult,improved intestinal inflammatory markers,ameliorated intestinal injury,reduced intestinal permeability,improved the reduction of tight junction proteins and prevented secondary IAH.And the activation of p38 MAPK by resuscitation following trauma-hemorrhage was reduced by melatonin.Administration of SB203580 abolished the increase of p38 MAPK and may also have some beneficial effect on intestine,but the effect was inferior to melatonin.Conclusions:1.A rat model of secondary IAH was successfully established by LR resuscitation after a combination of generating portal hypertension,hemorrhaging to a MAP of 40 mm Hg for 2 hrs and utilizing an abdominal restraint device.2.Compared with HS,and HES,melatonin was associated with less inflammatory and oxidative injury,less intestinal permeability and injury,and lower incidence of secondary IAH in this model.3.Our results collectively demonstrate that melatonin ameliorates intestinal injury and prevents secondary IAH in this rats model by the inhibition of p38 MAPK signaling pathway.