Clinical peritoneal dialysis solutions modulate white blood cell-intestinal vascular endothelium interaction

Direct peritoneal resuscitation augments ileal blood flow in necrotizing enterocolitis via a novel mechanism

PURPOSE

Endothelin-1, prostaglandins (PGs), and nitric oxide (NO) have been implicated in the intestinal microvascular dysfunction of necrotizing enterocolitis (NEC). We hypothesized that direct peritoneal resuscitation (DPR) dilates the intestinal microvasculature and improves blood flow independent of these mechanisms.

METHODS

Rat pups were assigned by litter to experimental NEC or CONTROL groups. Laser Doppler flowmetry evaluation of intestinal microvascular blood flow was studied at baseline, with mediator blockade (endothelin-A receptor, endothelin-B receptor, PG synthesis, or NO synthase) and with DPR. Repeated-measures analysis of variance test was applied with Tukey-Kramer honestly significant difference test (P < .05).

RESULTS

At baseline, NEC animals demonstrated significantly decreased ileal blood flow as compared with CONTROLs (P < .05). Endothelin-A receptor and PG inhibition increased flow in the intestinal microvasculature, but this was significantly augmented by the addition of DPR (P < .05). Blockade of NO synthase decreased intestinal blood flow, which was overcome with addition of DPR (P < .05).

CONCLUSION

Ileal blood flow was significantly reduced in NEC animals as compared with CONTROLs. The addition of DPR to the peritoneum increased ileal blood flow significantly in all groups in spite of blockade of these known vasoactive mechanisms. Direct peritoneal resuscitation may be a novel strategy to improve intestinal blood flow in NEC.

A new model of severe hemorrhagic shock in rats

We here introduce a fixed-pressure model of hemorrhagic shock in rats that maximizes effects on mean arterial blood pressure (MAP) during shock and yet maintains high reproducibility and controllability. The MAP of rats was adjusted to 25 to 30 mm Hg by blood withdrawals during 30 min. After a shock period of 60 min, rats were resuscitated either with lactated Ringer solution (LR) only or with the collected blood 3-fold diluted with LR (LR + blood) and monitored for further 150 min. Throughout the experiment, vital parameters and plasma marker enzyme activities and creatinine concentration were assessed. Thereafter, liver, kidneys, small intestine, heart, and lung were harvested and evaluated histopathologically. Vital parameters, plasma marker enzyme activities, creatinine concentration, and histopathology indicated pronounced but reliable and reproducible systemic effects and marked organ damage due to hemorrhagic shock and resuscitation. In contrast to rats that received LR + blood, which survived the postresuscitation period, rats receiving LR only invariably died shortly after resuscitation. The hemorrhagic shock model we present here maximally affects MAP and yet is highly reproducible in rats, allowing the study of various aspects of hemorrhagic shock and resuscitation under clinically relevant conditions.

Postresuscitation tissue neutrophil infiltration is time-dependent and organ-specific

BACKGROUND

Hemorrhagic shock with conventional resuscitation (CR) primes circulating neutrophils and activates vascular endothelium for increased systemic inflammation, superoxide release, and end-organ damage. Adjunctive direct peritoneal resuscitation (DPR) with intraperitoneal instillation of a clinical peritoneal dialysis solution decreases systemic inflammation and edema formation by enhancing tissue perfusion. The aim of this study is to determine the effect of adjunctive DPR on neutrophil and fluid sequestration.

METHODS

Anesthetized rats were hemorrhaged to 40% mean arterial pressure for 60 min. Animals were randomized for CR with the return of the shed blood plus two volumes of saline, or CR plus adjunctive DPR with 30 mL of intraperitoneal injection of a clinical peritoneal dialysis solution. Tissue myeloperoxidase (MPO) level, a marker of neutrophil sequestration, and total water content were assessed in the gut, lung, and liver in sham animals and at time-points 1, 2, 4, and 24 h postresuscitation.

RESULTS

Resuscitation from hemorrhagic shock increases MPO level in all tissues in a near-linear fashion during the first 4 h following resuscitation. This occurs irrespective of the resuscitation regimen used. Tissue MPO level returned to baseline at 24 h following resuscitation except in the liver where CR and not adjunctive DPR caused a significant rebound increase. Adjunctive DPR prevented the CR-mediated obligatory fluid sequestration in the gut and lung and maintained a relative normal tissue water in these organs compared with CR alone (n = 7, F = 10.1, P < 0.01).

CONCLUSION

Hemorrhagic shock and resuscitation produces time-dependent organ-specific trends of neutrophil sequestration as measured with tissue levels of myeloperoxidase, a marker of neutrophil infiltration. Modulation of the splanchnic blood flow by direct peritoneal resuscitation did not alter the time-dependent neutrophil infiltration in end-organs, suggesting a subordinate role of blood rheology in the hemorrhage-induced neutrophil sequestration. Vulnerable window for neutrophil-mediated tissue damage exists during the first 4 h following resuscitation from hemorrhagic shock in rats. Direct peritoneal resuscitation prevents the early obligatory fluid sequestration and promotes early fluid mobilization.