Plasma resuscitation improves and restores intestinal microcirculatory physiology following haemorrhagic shock

BACKGROUND AND OBJECTIVES

Intestinal ischaemia-reperfusion injury following resuscitated haemorrhagic shock (HS) leads to endothelial and microcirculatory dysfunction and intestinal barrier breakdown. Although vascular smooth muscle machinery remains intact, microvascular vasoconstriction occurs secondary to endothelial cell dysfunction, resulting in further ischaemia and organ injury. Resuscitation with fresh frozen plasma (FFP) improves blood flow, stabilizes the endothelial glycocalyx and alleviates organ injury. We postulate these improvements correlate with decreased tissue CO2 concentrations, improved microvascular oxygenation and attenuation of intestinal microvascular endothelial dysfunction.

MATERIALS AND METHODS

Male Sprague-Dawley rats were randomly assigned to groups (n = 8/group): (1) sham, (2) HS (40% mean arterial blood pressure [MAP], 60 min) + crystalloid resuscitation (CR) (shed blood saline) and (3) HS + FFP (shed blood + FFP). MAP, heart rate (HR), ileal perfusion, pO2 and pCO2 were measured at intervals until 4 h post-resuscitation (post-RES). At 4 h post-RES, the ileum was rinsed in situ with Krebs solution. Topical acetylcholine and then nitroprusside were applied for 10 min each. Serum was obtained, and after euthanasia, tissues were harvested and snap-frozen in liquid N2 and stored at -80°C.

RESULTS

FFP resuscitation resulted in sustained ileal perfusion as well as rapid sustained return to baseline microvascular pO2 and pCO2 values when compared to CR (p < 0.05). Endothelial function was preserved relative to sham in the FFP group but not in the CR group (p < 0.05).

CONCLUSION

FFP-based resuscitation improves intestinal perfusion immediately following resuscitation, which correlates with improved tissue oxygenation and decreased tissue CO2 levels. CR resulted in significant damage to endothelial vasodilation response to acetylcholine, while FFP preserved this function.

Plasma resuscitation with adjunctive peritoneal resuscitation reduces ischemia-induced intestinal barrier breakdown following hemorrhagic shock

INTRODUCTION

Hemorrhagic shock (HS) and resuscitation (RES) cause ischemia-induced intestinal permeability due to intestinal barrier breakdown, damage to the endothelium, and tight junction (TJ) complex disruption between enterocytes. The effect of hemostatic RES with blood products on this phenomenon is unknown. Previously, we showed that fresh frozen plasma (FFP) RES, with or without directed peritoneal resuscitation (DPR) improved blood flow and alleviated organ injury and enterocyte damage following HS/RES. We hypothesized that FFP might decrease TJ injury and attenuate ischemia-induced intestinal permeability following HS/RES.

METHODS

Sprague-Dawley rats were randomly assigned to groups (n = 8): sham; crystalloid resuscitation (CR) (HS of 40% mean arterial pressure for 60 minutes) and CR (shed blood plus two volumes of CR); CR and DPR (intraperitoneal 2.5% peritoneal dialysis fluid); FFP (shed blood plus one volume of FFP); and FFP and DPR (intraperitoneal dialysis fluid plus two volumes of FFP). Fluorescein isothiocyanate-dextran (molecular weight, 4 kDa; FD4) was instilled into the gastrointestinal tract before hemorrhage; FD4 was measured by UV spectrometry at various time points. Plasma syndecan-1 and ileum tissue TJ proteins were measured using enzyme-linked immunosorbent assay. Immunofluorescence was used to visualize claudin-4 concentrations at 4 hours following HS/RES.

RESULTS

Following HS, FFP attenuated FD4 leak across the intestine at all time points compared with CR and DPR alone. This response was significantly improved with the adjunctive DPR at 3 and 4 hours post-RES (p < 0.05). Resuscitation with FFP-DPR increased intestinal tissue concentrations of TJ proteins and decreased plasma syndecan-1. Immunofluorescence demonstrated decreased mobilization of claudin-4 in both FFP and FFP-DPR groups.

CONCLUSION

Fresh frozen plasma-based RES improves intestinal TJ and endothelial integrity. The addition of DPR can further stabilize TJs and attenuate intestinal permeability. Combination therapy with DPR and FFP to mitigate intestinal barrier breakdown following shock could be a novel method of reducing ischemia-induced intestinal permeability and systemic inflammation after trauma.

LEVEL OF EVIDENCE

Prognostic/Epidemiologic, Level III.

Vasoactive Components of Dialysis Solution

Background

Conventional peritoneal dialysis (PD) solutions elicit vasodilation, which is implicated in the variable rate of solute transport during the dwell. The components causing such vasoactivity are still controversial. This study was conducted to define the vasoactive components of conventional and new PD solutions.

Methods

Three visceral peritoneal microvascular levels were visualized by intravital video microscopy of the terminal ileum of anesthetized rats. Anesthesia-free decerebrate conscious rats served as control. Microvascular diameter and blood flow by Doppler measurements were conducted after topical peritoneal exposure to 4 clinical PD solutions and 6 prepared solutions designed to isolate potential vasoactive components of the PD solution.

Results

All clinically available PD solutions produced a rapid and generalized vasodilation at all intestinal microvascular levels, regardless of the osmotic solute. The pattern and magnitude of this dilation was not affected by anesthesia but was determined by arteriolar size, the osmotic solute, and the solution's buffer anion system. The greatest dilation occurred in the small precapillary arterioles and was elicited by conventional PD solution and heat re-sterilized solution containing low glucose degradation products (GDPs). Hypertonic mannitol solutions produced a dilation that was approximately 50% less than the dilation obtained with glucose solutions with identical osmolarity and buffer. Increasing a solution's osmolarity did not produce a parallel increase in the magnitude of dilation, suggesting a nonlinear relationship between the two variables. Lactate dissolved in an isotonic solution was completely non-vasoactive unless the solution's H+concentration was increased. At low pH, isotonic lactate produced a rapid but transient vasodilation. This vascular reactivity was similar in magnitude and pattern to that obtained with the isotonic 7.5% icodextrin solution (Extraneal; Baxter Healthcare, Deerfield, Illinois, USA).

Conclusions

( 1 ) Hyperosmolarity is the major vasoactive component of PD solution. ( 2 ) Hyperosmolarity and active intracellular glucose uptake account together for approximately 75% of PD solution-induced dilation, whereas GDPs contribute to approximately 25%. ( 3 ) Lactate is vasoactive only at low pH (high [H+]). ( 4 ) The magnitude of PD solution-mediated vasodilation is partially dependent on the nature of the osmotic solute, the GDP contents, and the [H+], which determine the vasoactivity of the lactate-buffer anion system. Studies are required to define the molecular mechanisms of PD-induced vasodilation and to determine the vasoactive properties of these solutions after chronic infusion.

Direct Peritoneal Resuscitation Reduces Lung Injury and Caspase 8 Activity in Brain Death

Background: Acute brain death (ABD) is associated with inflammation and lung injury. Direct peritoneal resuscitation (DPR) improves blood flow to the vital organs after ABD. DPR reduces lung injury, but the mechanism for this is unknown. Methods: Male Sprague-Dawley rats were randomized to five groups (n = 8/group): (1) Sham (no ABD); (2) Targeted intravenous fluid (TIVF) (ABD plus enough IVF to maintain a MAP of 80 mmHg) at 2 hours post-resuscitation (RES); (3) ABD + TIVF + DPR (TIVF and 30 cc intraperitoneal 2.5% Delflex) at 2 hours post-RES; (4) ABD + TIVF at 4 hours post-RES; and (5) ABD + TIVF + DPR at 4 hours post-RES. Messenger RNA (mRNA) levels were measured using Qiagen qRT PCR. Protein levels were assessed using quantitative ELISAs and the Luminex MagPix system. Results: Use of DPR caused 5.8-fold downregulation of mRNA expression for TNF-α and 2.7-fold decrease for the TNF receptor compared to TIVF alone. Caspase 8 mRNA was also downregulated. Protein levels for TNF-α, TNF receptor, caspase 8, NFκB, and NFκB inhibitor kinase, which promotes dissociation of NFκB inhibitor, were reduced by DPR. Cell death markers M30 and M65 were also decreased with DPR. Conclusions: Use of DPR caused changes in the expression of multiple mRNAs and proteins in the caspase 8 apoptotic pathway. These data represent a mechanism through which DPR exerts its beneficial effects within the lung tissue.

Direct peritoneal resuscitation reduces inflammation in the kidney after acute brain death

Brain death is associated with significant inflammation within the kidneys, which may contribute to reduced graft survival. Direct peritoneal resuscitation (DPR) has been shown to reduce systemic inflammation after brain death. To determine its effects, brain dead rats were resuscitated with normal saline (targeted intravenous fluid) to maintain a mean arterial pressure of 80 mmHg; DPR animals also received 30 cc of intraperitoneal peritoneal dialysis solution. Rats were euthanized at 0, 2, 4, and 6 h after brain death. Pro-inflammatory cytokines were measured using ELISA. Levels of IL-1β, TNF-α, and IL-6 in the kidney were significantly increased as early as 2 h after brain death and significantly decreased with DPR. Levels of leukocyte adhesion molecules ICAM and VCAM increased after brain death and were decreased with DPR (ICAM 2.33 ± 0.14 vs. 0.42 ± 0.04, P = 0.002; VCAM 82.6 ± 5.8 vs. 37.3 ± 1.9, P = 0.002 at 4 h) as were E-selectin and P-selectin (E-selectin 25,605 vs. 16,144, P = 0.005; P-selectin 82.5 ± 3.3 vs. 71.0 ± 2.3, P = 0.009 at 4 h). Use of DPR reduces inflammation and adhesion molecule expression in the kidneys, and is associated with reduced macrophages and neutrophils on immunohistochemistry. Using DPR in brain dead donors has the potential to reduce the immunologic activity of transplanted kidneys and could improve graft survival.

Damage-associated molecular patterns in resuscitated hemorrhagic shock are mitigated by peritoneal fluid administration

Conventional resuscitation (CR) of hemorrhagic shock (HS), a significant cause of trauma mortality, is intravenous blood and fluids. CR restores central hemodynamics, but vital organ flow can drop, causing hypoperfusion, hypoxia, damage-associated molecular patterns (DAMPs), and remote organ dysfunction (i.e., lung). CR plus direct peritoneal resuscitation (DPR) prevents intestinal and hepatic hypoperfusion. We hypothesized that DPR prevents lung injury in HS/CR by altering DAMPs. Anesthetized male Sprague-Dawley rats were randomized to groups ( n = 8/group) in one of two sets: 1) sham (no HS, CR, or DPR), 2) HS/CR (HS = 40% mean arterial pressure (MAP) for 60 min, CR = shed blood + 2 volumes normal saline), or 3) HS/CR + DPR. The first set underwent whole lung blood flow by colorimetric microspheres. The second set underwent tissue collection for Luminex, ELISAs, and histopathology. Lipopolysaccharide (LPS) and DAMPs were measured in serum and/or lung, including cytokines, hyaluronic acid (HA), high-mobility group box 1 (HMGB1), Toll-like receptor 4 (TLR4), myeloid differentiation primary response 88 protein (MYD88), and TIR-domain-containing adapter-inducing interferon-β (TRIF). Statistics were by ANOVA and Tukey-Kramer test with a priori P < 0.05. HS/CR increased serum LPS, HA, HMGB1, and some cytokines [interleukin (IL)-1α, IL-1β, IL-6, and interferon-γ]. Lung TLR4 and MYD88 were increased but not TRIF compared with Shams. HS/CR + DPR decreased LPS, HA, cytokines, HMGB1, TLR4, and MYD88 levels but did not alter TRIF compared with HS/CR. The data suggest that gut-derived DAMPs can be modulated by adjunctive DPR to prevent activation of lung TLR-4-mediated processes. Also, DPR improved lung blood flow and reduced lung tissue injury. Adjunctive DPR in HS/CR potentially improves morbidity and mortality by downregulating the systemic DAMP response.

Randomized Controlled Trial Evaluating the Efficacy of Peritoneal Resuscitation in the Management of Trauma Patients Undergoing Damage Control Surgery

BACKGROUND

Peritoneal resuscitation (PR) represents a unique modality of treatment for severely injured trauma patients requiring damage control surgery. These data represent the outcomes of a single institution randomized controlled trial into the efficacy of PR as a management option in these patients.

STUDY DESIGN

From 2011 to 2015, one hundred and three patients were enrolled in a prospective randomized controlled trial evaluating the use of PR in the treatment of patients undergoing damage control surgery compared with conventional resuscitation (CR) alone. Patient demographics, clinical variables, and outcomes were collected. Univariate and multivariate analysis was performed with a priori significance at p ≤ 0.05.

RESULTS

After initial screening, 52 patients were randomized to the PR group and 51 to the CR group. Age, sex, initial pH, and mechanism of injury were used for randomization. Method of abdominal closure was standardized across groups. Time to definitive abdominal closure was reduced in the PR group compared with the CR group (4.1 ± 2.2 days vs 5.9 ± 3.5 days; p ≤ 0.002). Volume of resuscitation and blood products transfused in the initial 24 hours was not different between the groups. Primary fascial closure rate was higher in the PR group (83% vs 66%; p ≤ 0.05). Intra-abdominal complications were lower in the PR compared with the CR group (8% vs 18%), with abscess formation rate (3% vs 14%; p < 0.05) being significant. Patients in the PR group had a lower 30-day mortality rate, despite similar Injury Severity Scores (13% vs 28%; p = 0.06).

CONCLUSIONS

Peritoneal resuscitation enhances management of damage control surgery patients by reducing time to definitive abdominal closure, intra-abdominal infections, and mortality rates.

Association Between MC-2 Peptide and Hepatic Perfusion and Liver Injury Following Resuscitated Hemorrhagic Shock

IMPORTANCE

Hemorrhagic shock (HS) due to trauma remains a major cause of morbidity and mortality in the United States, despite continuing progression of advanced life support and treatment. Trauma is the third most common cause of death worldwide and is the leading cause of death in the 1- to 44-year-old age group. Hemorrhagic shock often progresses to multiple organ failure despite conventional resuscitation (CR) that restores central hemodynamics.

OBJECTIVE

To examine whether MC-2 would bind glycosaminoglycans to decrease proinflammatory cytokines' influence in the liver, minimize organ edema, prevent liver injury, and improve hepatic perfusion. MC-2, a synthetic octapeptide derived from the heparin-binding domain of murine interferon gamma (IFN-γ), binds glycosaminoglycans to modulate serum and interstitial cytokine levels and activity.

DESIGN, SETTING, AND PARTICIPANTS

A controlled laboratory study of 3y male Sprague-Dawley rats that were randomized to 4 groups of 8 each: sham, sham+MC-2 (50 mg/kg), HS/CR, or HS/CR+MC-2 (HS = 40% of baseline mean arterial pressure for 60 minutes; CR = return of shed blood and 2 volumes of saline). The study began in March, 2013.

MAIN OUTCOMES AND MEASURES

Effective hepatic blood flow (EHBF) by galactose clearance, wet-dry weights, cytokines, histopathology, complete metabolic panel, and complete blood cell count were performed at 4 hours after CR.

RESULTS

MC-2 partially reversed the HS/CR-induced hepatic hypoperfusion at 3 and 4 hours postresuscitation compared with HS/CR alone. Effective hepatic blood flow decreased during the HS period from a mean (SD) of 7.4 (0.3) mL/min/100 g and 7.5 (0.5) mL/min/100g at baseline to 3.7 (0.4) mL/min/100g and 5.9 (0.5) mL/min/100g for the HS/CR and HS/CR+MC-2 groups, respectively (P <.05). Effective hepatic blood flow remained constant in the sham groups throughout the experimental protocol. Organ edema was increased in the ileum and liver in the HS/CR vs sham group, and MC-2 decreased edema in the ileum vs the HS/CR group. MC-2 in HS also decreased levels of alanine aminotransferase, zonula occludens-1, and interleukin-1β compared with HS/CR alone.

CONCLUSIONS AND RELEVANCE

MC-2 was associated with decreased liver injury, enhanced effective hepatic blood flow, decreased cytokines, and prevention of edema formation in the ileum when administered with CR following HS. These data suggest that the MC-2 peptide could be a potential therapeutic approach to target cytokine and chemokine interactions, which might limit multiple organ failure and decrease mortality in hemorrhagic shock.

Direct Peritoneal Resuscitation Alters Hepatic miRNA Expression after Hemorrhagic Shock

BACKGROUND

MicroRNAs (miRNAs) are small segments of noncoding RNA that regulate gene expression and protein function, and therefore are key regulators of cellular processes including those of the inflammatory cascade after hemorrhagic shock (HS). We have previously shown that direct peritoneal resuscitation (DPR), as an adjunct to traditional IV fluid resuscitation, improves visceral blood flow and reduces pro-inflammatory cytokines released during HS. The effects of DPR on hepatic miRNA (miR) expression patterns after resuscitated HS are not known.

STUDY DESIGN

Male Sprague-Dawley rats were divided into 3 groups: sham (no HS); conventional resuscitation (CR; HS, then resuscitated with shed blood and 2 volumes of saline); and DPR (CR plus 30 mL peritoneal dialysis solution). Animals were sacrificed at 4 hours, and miRNAs were measured using reverse transcription polymerase chain reaction.

RESULTS

Use of DPR downregulated 68 of 92 hepatic miRNAs compared with only 2 of 92 upregulated when compared with CR alone, p < 0.01). Specifically, miR-9-5p, miR-122-5p, and miR-146, which regulate NFκB, were downregulated 4.1-, 3.4-, and 0.86-fold, respectively; miR-29a and miR-126 were upregulated 0.88- and 3.7-fold when DPR was compared with CR.

CONCLUSIONS

Adding DPR downregulated most hepatic miRNAs compared with CR alone. Some miRNAs were affected more significantly, suggesting that although this clinical intervention causes a near-global downregulation of hepatic miRNA, it still targets specific inflammatory pathways. Use of DPR for resuscitation of patients in HS may reduce hepatic inflammation to improve patient outcomes after hemorrhage.

Resveratrol decreases nitric oxide production by hepatocytes during inflammation

INTRODUCTION

The production of excessive amounts of nitric oxide (NO) through inducible nitric oxide synthase (iNOS) contributes to organ injury, inflammation, and mortality after shock. Resveratrol (RSV) is a natural polyphenol that decreases shock-induced hepatic injury and inflammation. We hypothesized that RSV would mediate these effects by decreasing hepatocyte iNOS production.

METHODS

Rat hepatocytes were isolated, cultured with varying concentrations of RSV, and then stimulated to induce iNOS with interleukin-1 and interferon. Induction of iNOS protein was measured by Western blot, iNOS mRNA by polymerase chain reaction, and NO production was measured by culture supernatant nitrite. Activation of intracellular signaling pathways involving Akt, c-Jun N-terminal kinase (JNK), and nuclear factor κB (NF-κB) were measured by Western blot using isoform-specific antibodies.

RESULTS

RSV decreased the expression of iNOS mRNA, protein, and supernatant nitrite in a dose-dependent manner. Our previous work demonstrated that Akt and JNK both inhibit hepatic iNOS production, whereas NF-κB increases iNOS expression. Analysis of signaling pathways in this study demonstrated that RSV increased JNK phosphorylation but decreased Akt phosphorylation and increased NF-κB activation.

CONCLUSION

RSV decreases cytokine-induced hepatocyte iNOS expression, possibly through up-regulation of the JNK signaling pathway. RSV merits further investigation to determine its mechanism as a compound that can decrease inflammation after shock.

Addition of direct peritoneal lavage to human cadaver organ donor resuscitation improves organ procurement

BACKGROUND

Brain dead organ donors have altered central hemodynamic performance, impaired hormone physiology, exaggerated systemic inflammatory response, end-organ microcirculatory dysfunction, and tissue hypoxia. A new treatment, direct peritoneal resuscitation (DPR), stabilizes vital organ blood flow after conventionally resuscitated shock to improve these derangements.

STUDY DESIGN

A prospective case-control study of adjunctive DPR compared 26 experimental patients (brain dead organ donors) to 52 controls (protocolized conventionally resuscitated donors). Actual organ procurement rates were compared with the Scientific Registry of Transplant Recipient predicted organ yield per patient. Achievement of donor management goals and effective hepatic blood flow were recorded.

RESULTS

Fourteen of 26 (53.8%) patients treated with DPR achieved all donor management goals compared with 17 of 52 (32.7%) patients treated with conventionally resuscitated (odds ratio = 2.4; 95% CI, 0.92-6.3; p = 0.06). Patients treated with DPR were more than 2 times as likely to achieve final pO2 >100 on 40% FiO2 compared with controls (odds ratio = 2.8; 95% CI, 1-7.69; p = 0.03). Also, DPR-treated patients required less IV crystalloid during the first 12 hours of management (DPR: 3,167 ± 1,893 mL vs 4,154 ± 2,100 mL; p = 0.046) and required less vasopressor agents at 12 hours post resuscitation (odds ratio = 7.7; 95% CI, 0.82-42; p = 0.02). Direct peritoneal resuscitation patients had enhanced effective hepatic blood flow and significantly higher organs transplanted per donor rates compared with controls (3.7 ± 1.7 vs 3.1 ± 1.3; p = 0.024).

CONCLUSIONS

Direct peritoneal resuscitation reduced IV fluid requirement and IV pressor use as well as increased hepatic blood flow and organs transplanted per donor. Direct peritoneal resuscitation studies show it to be a safe, effective method to augment organ donor resuscitation and additional large-scale trials should be conducted to validate these findings.

Targeted Physician Education Positively Affects Delivery of Nutrition Therapy and Patient Outcomes: Results of a Prospective Clinical Trial

BACKGROUND

Malnutrition is a continuing epidemic among hospitalized patients. We hypothesize that targeted physician education should help reduce caloric deficits and improve patient outcomes.

MATERIALS AND METHODS

We performed a prospective trial of patients (n = 121) assigned to 1 of 2 trauma groups. The experimental group (EG) received targeted education consisting of strategies to increase delivery of early enteral nutrition. Strategies included early enteral access, avoidance of nil per os (NPO) and clear liquid diets (CLD), volume-based feeding, early resumption of feeds postprocedure, and charting caloric deficits. The control group (CG) did not receive targeted education but was allowed to practice in a standard ad hoc fashion. Both groups were provided with dietitian recommendations on a multidisciplinary nutrition team per standard practice.

RESULTS

The EG received a higher percentage of measured goal calories (30.1 ± 18.5%, 22.1 ± 23.7%, P = .024) compared with the CG. Mean caloric deficit was not significantly different between groups (-6796 ± 4164 kcal vs -8817 ± 7087 kcal, P = .305). CLD days per patient (0.1 ± 0.5 vs 0.6 ± 0.9), length of stay in the intensive care unit (3.5 ± 5.5 vs 5.2 ± 6.8 days), and duration of mechanical ventilation (1.6 ± 3.7 vs 2.8 ± 5.0 days) were all reduced in the EG compared with the CG (P < .05). EG patients had fewer nosocomial infections (10.6% vs 23.6%) and less organ failure (10.6% vs 18.2%) than did the CG, but these differences did not reach statistical significance.

CONCLUSION

Implementation of specific educational strategies succeeded in greater delivery of nutrition therapy, which favorably affected patient care and outcomes.

Oral relaxin maintains intestinal blood flow in a rat model of NEC

PURPOSE

Intestinal vasoconstriction is a critical step in development of necrotizing enterocolitis (NEC). Relaxin (RLXN), a hormone found in breast milk but absent from formula, is a potent vasodilator. We hypothesized that relaxin-supplemented feeds with an NEC protocol would decrease NEC severity and increase intestinal blood flow.

METHODS

Timed-pregnant Sprague-Dawley rats were randomly assigned to CONTROL, NEC, NEC+1xRLXN, or NEC+All Feeds RLXN, and all but CONTROL underwent NEC protocol. NEC+1xRLXN and NEC+All Feeds RLXN groups were fed relaxin-supplemented formula with the last feed or every feed. At 48h of life, intestinal blood flow was measured at baseline and after application of 2.5% Delflex® solution.

RESULTS

The addition of relaxin to NEC group feeds (1x or All Feeds) improved the degree of ileal injury. Ileal blood flow was decreased in the NEC pups compared to the CONTROLS, but the addition of relaxin to one feed increased baseline ileal blood flow in the NEC group compared to NEC alone. Furthermore, the addition of relaxin to ALL feeds significantly increased baseline ileal blood flow.

CONCLUSION

Pups who received relaxin with all feeds had substantially increased ileal perfusion compared to control pups. Our data suggest that relaxin supplementation maintains intestinal blood flow and results in less histologic NEC.

Increased hepatic blood flow during enteral immune-enhancing diet gavage requires intact enterohepatic bile cycling

OBJECTIVES

Total hepatic blood flow (HBF) via the hepatic artery and portal vein is highly dependent on gastrointestinal perfusion. During postprandial hyperemia, intestinal blood flow depends on nutrient composition, gastrointestinal location, and time. Immune-enhancing diets (IEDs) containing n-3 polyunsaturated fatty acids (PUFAs) selectively augment blood flow in the ileum at 60-120 min via a bile-dependent mechanism. My colleagues and I hypothesized that liver blood flow would be similarly affected by IEDs containing n-3 PUFAs.

METHODS

Mean arterial blood pressure, heart rate, and effective HBF (galactose clearance) were measured in anesthetized male Sprague-Dawley rats after gastric gavage of either a control diet (CD, Boost, Novartis) or an IED (Impact, Nestle Nutrition), with or without bile-duct ligation (BDL), and with or without supplemental bile (bovine, dried, unfractionated). Significance was assessed by 2-way ANOVA for repeated measures with the Tukey-Kramer honestly significant difference test.

RESULTS

Compared with baseline levels, a CD increased HBF (peak at 40 min , *P < 0.05) whereas an IED increased HBF in two distinct peaks at 40 min (*P < 0.05) and 120 min (*P < 0.05), but BDL prevented both the early (CD and IED, †P < 0.05) and late peaks (IED, †P < 0.05). Bile supplementation in the CD + BDL or IED + BDL groups restored neither the CD peak nor the early or late IED peaks.

CONCLUSIONS

HBF during absorptive intestinal hyperemia is modulated by a mechanism that requires an intact enterohepatic circulation. The early peaks at 40 min (CD or IED) were prevented by BDL, even though fat absorption in the proximal gut occurs by bile-independent direct absorption. Bile supplementation with the diet (CD + BDL or IED + BDL) was insufficient to restore HBF hyperemia, which implies that a relationship exists between intestinal and hepatic blood flow that is not solely dependent on bile-mediated intestinal fat absorption and bile recirculation.

Fish oil increases blood flow in the ileum during chronic feeding in rats

Benefits of enteral feeding with immune-enhancing diets (IEDs) depend on route, timing, and composition. We hypothesized that chronic enteral feeding with certain individual immunonutrients would enhance gastrointestinal blood flow. Male rats were fed a standard enteral diet supplemented with immunonutrients for 5 days before study. Groups were (1) standard rat chow, (2) liquid control diet (CD) alone (CD), (3) CD + fish oil, (4) CD + L-arginine, and (5) CD + RNA fragments. Whole organ blood flow distribution was measured by colorimetric microsphere technique in antrum, small intestine (in thirds), colon, liver, spleen, pancreas, and kidneys. Chronic feeding for 5 days with CD + fish oil increased blood flow in the distal third of the small intestine compared with CD alone, whereas feeding with CD + L-arginine decreased blood flow in the small intestine (all segments) compared with CD alone. Acute gavage of CD + L-arginine or CD + fish oil increased blood flow in the proximal and middle third of the small intestine compared with CD alone. Control diet + RNA increased blood flow in the proximal small intestine compared with CD alone. These findings support prior acute feeding studies with CD, CD + individual immunonutrients, or IED. Our current data suggest that blood flow benefits associated with fish oil persist during chronic feeding in rats. Enhanced gastrointestinal perfusion might partially explain the benefits of early enteral feeding with IEDs not seen with regular enteral diets and parenteral immunonutrient delivery.

Preservation of hepatic blood flow by direct peritoneal resuscitation improves survival and prevents hepatic inflammation following hemorrhagic shock

Conventional resuscitation (CR) from hemorrhagic shock (HS) results in gut and liver hypoperfusion, organ and cellular edema, and vital organ injury. Adjunct direct peritoneal resuscitation (DPR) with dialysate prevents gut vasoconstriction, hypoperfusion, and injury. We hypothesized that DPR might also improve hepatocellular edema, inflammation, and injury. Anesthetized male SD rats were assigned to groups (n = 8/group): 1) sham (no HS); 2) HS (40% MAP/60 min) + intravenous fluid conventional resuscitation [CR; shed blood + 2 vol saline (SAL)/30 min]; 3) HS+CR+DPR (30 ml ip 2.5% glucose dialysate); or 4) HS+CR+SAL (30 ml ip saline). Histopathology showed lung and liver injury in HS+CR and HS+CR+SAL up to 24-h postresuscitation (post-RES) that was not in shams and which was prevented by adjunct DPR. Wet-to-dry weight ratios in HS+CR revealed organ edema formation that was prevented by adjunct DPR. HS+CR and HS+CR+SAL had 34% mortality by 24-h post-RES, which was absent with DPR (0%). Liver IFN-γ and IL-6 levels were elevated in CR compared with DPR or shams. TNF-α mRNA was upregulated in CR/sham and DPR/sham. IL-17 was downregulated in DPR/sham. CXCL10 mRNA was upregulated in CR/sham but downregulated in DPR/sham. Despite restored central hemodynamic performance after CR of HS, liver blood flow was compromised up to 24 h post-RES, and the addition of DPR restores and maintains liver perfusion at 24-h post-RES. DPR prevented liver injury, histological damage, and edema formation compared with CR alone. DPR provided a mitigating anti-inflammatory dampening of the systemic inflammatory response. In all, these effects likely account for improved survivorship in the DPR-treated group.

Maternal cigarette smoking and the development of necrotizing enterocolitis

BACKGROUND

The maternal variables that affect fetal development and correlate with necrotizing enterocolitis (NEC), the most common gastrointestinal emergency in premature infants, are not well defined. We hypothesized that maternal risk factors were the primary determinant of future development of NEC.

METHODS

Patients with NEC were identified from an established NICU database and were control-matched with 2 neonates treated at the same institution. The medical records of each patient during the NICU admission as well as the prenatal and delivery record of the patient's mother were reviewed. Perinatal data, including maternal smoking, maternal hypertension, maternal BMI, maternal gestational diabetes, conduct of labor and type of delivery, Apgar scores, types of feedings, and placental pathology, were examined, with P < .05 deemed significant.

RESULTS

A total of 73 neonates diagnosed with NEC and 146 matched controls were identified. Medical records for each subject and their mothers were reviewed (438 records total). Maternal cigarette smoking was significantly associated with the future development of NEC (P = .02). Maternal gestational diabetes, maternal hypertension, formula feeding, and pathologic chorioamnionitis or uteroplacental insufficiency did not correlate with NEC.

CONCLUSIONS

These data identified maternal cigarette smoking as the only risk factor that is associated with the development of NEC in premature infants. Our data imply that smoking delivers toxins and nicotine to the uterine microenvironment that can affect microvascular development and may predispose the fetus to future NEC.

Intestinal microcirculatory flow alterations in necrotizing enterocolitis are improved by direct peritoneal resuscitation

Vasoconstriction of the neonatal intestinal microvasculature is a central mechanistic event in development of necrotizing enterocolitis. We hypothesized that topical treatment of the intestine with dialysate fluid would ameliorate the vasoconstriction in necrotizing enterocolitis (NEC). NEC was induced in experimental groups. Control animals were delivered vaginally and dam-fed (control group). Neonatal pups underwent laser Doppler flow study of the terminal ileum to determine real-time blood flow in the intestinal microvasculature. After baseline flow was determined, dialysis solution was added to the peritoneal cavity and alterations in microcirculation were recorded. Baseline ileal blood flow in the control group was significantly higher than in NEC rat pups at 48 hours post delivery (P < 0.05), but not at 24 hours (P = NS). Ileal blood flow increased in all groups after adding dialysate (P < 0.05), improving ileal blood flow in the 48-hour NEC group and reaching the baseline level of the 48-hour control group (P < 0.05). Our data shows blood flow to be higher in 48-hour controls as compared with 24-hour controls suggesting a time-dependency in the development of intestinal vasoregulatory processes. All groups had an increase in blood flow with dialysate treatment. This may represent a novel initial therapy to improve intestinal ischemia in human necrotizing enterocolitis.

Intestinal Microcirculatory Flow Alterations in Necrotizing Enterocolitis are Improved by Direct Peritoneal Resuscitation

Vasoconstriction of the neonatal intestinal microvasculature is a central mechanistic event in development of necrotizing enterocolitis. We hypothesized that topical treatment of the intestine with dialysate fluid would ameliorate the vasoconstriction in necrotizing enterocolitis (NEC). NEC was induced in experimental groups. Control animals were delivered vaginally and dam-fed (control group). Neonatal pups underwent laser Doppler flow study of the terminal ileum to determine real-time blood flow in the intestinal microvasculature. After baseline flow was determined, dialysis solution was added to the peritoneal cavity and alterations in microcirculation were recorded. Baseline ileal blood flow in the control group was significantly higher than in NEC rat pups at 48 hours post delivery ( P < 0.05), but not at 24 hours ( P = NS). Ileal blood flow increased in all groups after adding dialysate ( P < 0.05), improving ileal blood flow in the 48-hour NEC group and reaching the baseline level of the 48-hour control group ( P < 0.05). Our data shows blood flow to be higher in 48-hour controls as compared with 24-hour controls suggesting a time-dependency in the development of intestinal vasoregulatory processes. All groups had an increase in blood flow with dialysate treatment. This may represent a novel initial therapy to improve intestinal ischemia in human necrotizing enterocolitis.

Direct peritoneal resuscitation improves obesity-induced hepatic dysfunction after trauma

BACKGROUND

The metabolic syndrome and associated fatty liver disease are thought to contribute to poor outcomes in trauma patients. Experimentally, obesity compromises liver blood flow. We sought to correlate the effect of obesity, injury severity, and liver dysfunction with trauma outcomes. We hypothesized that obesity-related liver dysfunction could be mitigated with the novel technique of adjunctive direct peritoneal resuscitation (DPR).

STUDY DESIGN

This study has clinical and experimental arms. The clinical study was a case-controlled retrospective analysis of ICU trauma patients (n = 72 obese, n = 187 nonobese). The experimental study was a hemorrhagic shock model in obese rats to assess the effect of DPR on liver blood flow, liver function, and inflammatory mediators.

RESULTS

In trauma patients, univariate and multivariate analyses demonstrated increasing mortality (p < 0.05), septic complications (p < 0.05), liver dysfunction (p < 0.001), and renal impairment (p < 0.05) with increasing body mass index and injury severity score. Obesity in rats impairs liver blood flow, liver function, renal function, and inflammation (interleukin [IL]-1β, IL-6, high mobility group protein B1[HMGB-1]). The addition of DPR to shock resuscitation restores liver blood flow, improves organ function, and reverses the systemic proinflammatory response.

CONCLUSIONS

Our clinical review substantiates that obesity worsens trauma outcomes regardless of injury severity. Obesity-related liver and renal dysfunction is aggravated by injury severity. In an obese rat model of resuscitated hemorrhagic shock, the addition of DPR abrogates trauma-induced liver, renal, and inflammatory responses. We conclude that the addition of DPR to the clinical resuscitation regimen will benefit the obese trauma patient.

Altered intestinal microcirculation is the critical event in the development of necrotizing enterocolitis

PURPOSE

The pathophysiology of necrotizing enterocolitis (NEC) includes prematurity, enteral feeds, hypoxia, and hypothermia. We hypothesized that vasoconstriction of the neonatal intestinal microvasculature is the essential mechanistic event in NEC and that these microvascular changes correlate with alterations in mediators of inflammation.

METHODS

Sprague-Dawley rat pups were separated into groups by litter. Necrotizing enterocolitis was induced in experimental groups, whereas control animals were delivered vaginally and dam fed. Neonatal pups underwent intravital videomicroscopy of the terminal ileum with particular attention to the inflow and premucosal arterioles. Reverse transcriptase-polymerase chain reaction was performed to evaluate for messenger RNA of mediators of inflammation.

RESULTS

Necrotizing enterocolitis animals demonstrated statistically significant smaller inflow and premucosal arterioles than control animals (P < .05). Necrotizing enterocolitis animals had an altered intestinal arteriolar flow with a distinct "stop-and-go" pattern, suggesting severe vascular dysfunction. Reverse transcriptase-polymerase chain reaction confirmed elevation of Toll-like receptor 4 (P = .01) and high-mobility group box protein 1 (P = .001) in the ileum of animals with NEC.

CONCLUSION

Intestinal arterioles were significantly smaller at baseline in animals with NEC compared with controls, and expression of inflammatory mediators was increased in animals with NEC. This represents a novel method of defining the pathophysiology of NEC and allows real-time evaluation of novel vasoactive strategies to treat NEC.

Glucose-induced intestinal vasodilation via adenosine A1 receptors requires nitric oxide but not K(+)(ATP) channels

BACKGROUND

Both nitric oxide (NO) and adenosine A1 receptor activation mediate microvascular vasodilation during intestinal glucose absorption. Our overall hypothesis is that adenosine triphosphate (ATP) utilization during glucose absorption would increase adenosine metabolite release, which acts on adenosine A1 receptors to alter endothelial production of NO and/or activate ATP-dependent potassium channels (K(+)(ATP)) to dilate intestinal microvessels.

METHODS

Intravital videomicroscopy of the rat jejunum was used to record the vascular responses of inflow (termed 1A) arterioles, proximal (p3A), and distal (d3A) premucosal arterioles during exposure to isotonic glucose or mannitol solutions alone or in the presence of the selective nitric oxide synthase (NOS) inhibitor (L-NMMA), an adenosine A1 receptor antagonist (8-cyclopentyl-1,3-dipropylxanthine (DPCPX)), or a K(+)(ATP) channel inhibitor (glibenclamide).

RESULTS

As expected, glucose exposure caused rapid dilation of both p3A and d3A arterioles, while mannitol exposure had no effect on microvascular diameters. Adenosine A1 receptor blockade completely prevented glucose-induced dilation of the premucosal arterioles. NOS inhibition significantly blunted the glucose-induced vasodilation of the premucosal arterioles, but had little effect in the mannitol group. Simultaneous application of both the NOS inhibitor and the adenosine A1 receptor antagonist gave the same reduction in glucose-induced dilation of the premucosal arterioles as the adenosine A1 receptor antagonist alone. Blockade of K(+)(ATP) channels with glibenclamide did not attenuate glucose-induced vasodilation of the premucosal arterioles.

CONCLUSION

These data suggest that glucose-induced vasodilation of premucosal jejunal arterioles is mediated through adenosine A1 receptors, and NO at least partially mediates the adenosine A1 receptor-induced vasodilation. In addition, K(+)(ATP) channels are not involved in premucosal arteriolar vasodilation during intestinal glucose exposure.

Obesity-induced hepatic hypoperfusion primes for hepatic dysfunction after resuscitated hemorrhagic shock

BACKGROUND

Obese patients (BMI>35) after blunt trauma are at increased risk compared to non-obese for organ dysfunction, prolonged hospital stay, infection, prolonged mechanical ventilation, and mortality. Obesity and non-alcoholic fatty liver disease (NAFLD) produce a low grade systemic inflammatory response syndrome (SIRS) with compromised hepatic blood flow, which increases with body mass index. We hypothesized that obesity further aggravates liver dysfunction by reduced hepatic perfusion following resuscitated hemorrhagic shock (HEM).

METHODS

Age-matched Zucker rats (Obese, 314-519 g & Lean, 211-280 g) were randomly assigned to 4 groups (n = 10-12/group): (1) Lean-Sham; (2) Lean, HEM, and resuscitation (HEM/RES); (3) Obese-Sham; and (4) Obese-HEM/RES. HEM was 40% of mean arterial pressure (MAP) for 60 min; RES was return of shed blood/5 min and 2 volumes of saline/25 min. Hepatic blood flow (HBF) using galactose clearance, liver enzymes and complete metabolic panel were measured over 4 h after completion of RES.

RESULTS

Obese rats had increased MAP, heart rate, and fasting blood glucose and BUN concentrations compared to lean controls, required less blood withdrawal (mL/g) to maintain 40% MAP, and RES did not restore BL MAP. Obese rats had decreased HBF at BL and during HEM/RES, which persisted 4 h post RES. ALT and BUN were increased compared to Lean-HEM/RES at 4 h post-RES.

CONCLUSION

These data suggest that obesity significantly contributes to trauma outcomes through compromised vascular control or through fat-induced sinusoidal compression to impair hepatic blood flow after HEM/RES resulting in a greater hepatic injury. The pro-inflammatory state of NAFLD seen in obesity appears to prime the liver for hepatic ischemia after resuscitated hemorrhagic shock, perhaps intensified by insidious and ongoing hepatic hypoperfusion established prior to the traumatic injury or shock.

Modulation of mesenteric lymph flow and composition by direct peritoneal resuscitation from hemorrhagic shock

HYPOTHESIS

Traditional clinical resuscitation from hemorrhagic shock that focuses on restoring central hemodynamic function does not adequately perfuse the gut. Intestinal hypoperfusion could stimulate ongoing organ failure and gut-derived systemic inflammatory response syndrome. Direct peritoneal resuscitation (DPR) that uses dialysis fluid improves perfusion and survival. We examined mesenteric lymph flow and proinflammatory constituents to determine whether DPR-stabilized interstitial compartment function could explain improved outcomes.

DESIGN

A paired-control experimental animal study.

PARTICIPANTS

Mesenteric lymph fluid was continuously collected in 4 groups of rats (n = 7 per group): sham group; hemorrhagic shock (50% mean arterial pressure for 30 minutes) and resuscitation (shed blood plus 2 volumes of isotonic sodium chloride for 30 minutes) group; hemorrhagic shock and resuscitation plus intraperitoneal saline (30 mL) group; and hemorrhagic shock and resuscitation plus DPR (30 mL of 2.5% clinical peritoneal dialysis fluid).

INTERVENTIONS

Both DPR and saline were placed intraperitoneally at the time of resuscitation.

MAIN OUTCOME MEASURES

Lymph composition was analyzed by enzyme-linked immunosorbent assay (ELISA) for hyaluronic acid, its ligand CD44, and cytokines.

RESULTS

Hemorrhagic shock and resuscitation elevated lymph flow (peak mean [SEM], 20.6 [5.6] microL/min at 60 minutes after resuscitation) and CD44 serum levels (peak mean [SEM], 140.0 [12.9] ng/mL at 120 minutes after resuscitation) compared with the sham group (mean [SEM], 1.2 [0.7] microL/min and 15.6 [1.5] ng/mL), and DPR returned levels to baseline (mean [SEM], 4.4 [0.5] microL/min and 15.4 [0.3] ng/mL). Hyaluronic acid levels were elevated in the hemorrhagic shock and resuscitation group (mean [SEM], 90.0 [1.3] ng/mL) and the hemorrhagic shock and resuscitation plus intraperitoneal saline group (mean [SEM], 93.0 [1.3] ng/mL) compared with the sham group (mean [SEM], 73.7 [1.4] ng/mL) or DPR group (81.2 [0.9] ng/mL). Interferon gamma, interleukin 1beta, interleukin 6, and interleukin 10 levels were also modulated by DPR.

CONCLUSIONS

Hemorrhagic shock and resuscitation increased lymph flow by altering capillary water transport and expanding interstitial volume. Increased lymph hyaluronic acid and inflammatory cytokines with traditional resuscitation were modulated to sham levels by DPR. In addition, DPR reduces these patterns presumably via an osmotic effect on capillary water transport. Adjunctive DPR might offer novel protection from systemic inflammatory response syndrome after hemorrhagic shock and resuscitation.

Hemorrhage-induced hepatic injury and hypoperfusion can be prevented by direct peritoneal resuscitation

BACKGROUND

Crystalloid fluid resuscitation after hemorrhagic shock (HS) that restores/maintains central hemodynamics often culminates in multi-system organ failure and death due to persistent/progressive splanchnic hypoperfusion and end-organ damage. Adjunctive direct peritoneal resuscitation (DPR) using peritoneal dialysis solution reverses HS-induced splanchnic hypoperfusion and improves survival. We examined HS-mediated hepatic perfusion (galactose clearance), tissue injury (histopathology), and dysfunction (liver enzymes).

METHODS

Anesthetized rats were randomly assigned (n = 8/group): (1) sham (no HS); (2) HS (40% mean arterial pressure for 60 min) plus conventional i.v. fluid resuscitation (CR; shed blood + 2 volumes saline); (3) HS + CR + 30 mL intraperitoneal (IP) DPR; or (4) HS + CR + 30 mL IP saline. Hemodynamics and hepatic blood flow were measured for 2 h after CR completion. In duplicate animals, liver and splanchnic tissues were harvested for histopathology (blinded, graded), hepatocellular function (liver enzymes), and tissue edema (wet-dry ratio).

RESULTS

Group 2 decreased liver blood flow, caused liver injuries (focal to submassive necrosis, zones 2 and 3) and tissue edema, and elevated liver enzymes (alanine aminotransferase (ALT), 149 +/- 28 microg/mL and aspartate aminotransferase (AST), 234 +/- 24 microg/mL; p < 0.05) compared to group 1 (73 +/- 9 and 119 +/- 10 microg/mL, respectively). Minimal/no injuries were observed in group 3; enzymes were normalized (ALT 89 +/- 9 microg/mL and AST 150 +/- 17 microg/mL), and tissue edema was similar to sham.

CONCLUSIONS

CR from HS restored and maintained central hemodynamics but did not restore or maintain liver perfusion and was associated with significant hepatocellular injury and dysfunction. DPR added to conventional resuscitation (blood and crystalloid) restored and maintained liver perfusion, prevented hepatocellular injury and edema, and preserved liver function.

Vasoactive components of dialysis solution

BACKGROUND

Conventional peritoneal dialysis (PD) solutions elicit vasodilation, which is implicated in the variable rate of solute transport during the dwell. The components causing such vasoactivity are still controversial. This study was conducted to define the vasoactive components of conventional and new PD solutions.

METHODS

Three visceral peritoneal microvascular levels were visualized by intravital video microscopy of the terminal ileum of anesthetized rats. Anesthesia-free decerebrate conscious rats served as control. Microvascular diameter and blood flow by Doppler measurements were conducted after topical peritoneal exposure to 4 clinical PD solutions and 6 prepared solutions designed to isolate potential vasoactive components of the PD solution.

RESULTS

All clinically available PD solutions produced a rapid and generalized vasodilation at all intestinal microvascular levels, regardless of the osmotic solute. The pattern and magnitude of this dilation was not affected by anesthesia but was determined by arteriolar size, the osmotic solute, and the solution's buffer anion system. The greatest dilation occurred in the small precapillary arterioles and was elicited by conventional PD solution and heat re-sterilized solution containing low glucose degradation products (GDPs). Hypertonic mannitol solutions produced a dilation that was approximately 50% less than the dilation obtained with glucose solutions with identical osmolarity and buffer. Increasing a solution's osmolarity did not produce a parallel increase in the magnitude of dilation, suggesting a nonlinear relationship between the two variables. Lactate dissolved in an isotonic solution was completely non-vasoactive unless the solution's H(+) concentration was increased. At low pH, isotonic lactate produced a rapid but transient vasodilation. This vascular reactivity was similar in magnitude and pattern to that obtained with the isotonic 7.5% icodextrin solution (Extraneal; Baxter Healthcare, Deerfield, Illinois, USA).

CONCLUSIONS

(1) Hyperosmolarity is the major vasoactive component of PD solution. (2) Hyperosmolarity and active intracellular glucose uptake account together for approximately 75% of PD solution-induced dilation, whereas GDPs contribute to approximately 25%. (3) Lactate is vasoactive only at low pH (high [H(+)]). (4) The magnitude of PD solution-mediated vasodilation is partially dependent on the nature of the osmotic solute, the GDP contents, and the [H(+)], which determine the vasoactivity of the lactate-buffer anion system. Studies are required to define the molecular mechanisms of PD-induced vasodilation and to determine the vasoactive properties of these solutions after chronic infusion.

Obesity, inflammation, and the potential application of pharmaconutrition

Obesity is an emerging problem worldwide. Hospitalized obese patients often have a worse outcome than patients of normal weight, particularly in the setting of trauma and critical care. Obesity creates a low-grade systemic inflammatory response syndrome (SIRS) that is similar (but on a much smaller scale) to gram-negative sepsis. This process involves up-regulation of systemic immunity, is characterized clinically by insulin resistance and the metabolic syndrome, and puts the patient at increased risk for organ failure, infectious morbidity, and mortality. Through lipotoxicity and cytokine dysregulation, obesity may act to prime the immune system, predisposing to an exaggerated subsequent immune response when a second clinical insult occurs (such as trauma, burns, or myocardial infarction). Specialized nutrition therapy for such patients currently consists of a hypocaloric, high-protein diet. However, this approach does not address the putative pathophysiologic mechanisms of inflammation and altered metabolism associated with obesity. A number of dietary agents such as arginine, fish oil, and carnitine may correct these problems at the molecular level. Pharmaconutrition formulas may provide exciting innovations for the nutrition therapy of the obese patient.

Plasma appearance rate of intraperitoneal macromolecular tracer underestimates peritoneal lymph flow

The magnitude of peritoneal lymph flow is an issue of great controversy in peritoneal dialysis (PD) research. Because no single lymphatic duct drains the entire peritoneal cavity, peritoneal lymph flow is indirectly measured as lymphatic removal of intraperitoneal macromolecular tracer. In rats, the peritoneal clearance (K) of such a tracer is 5 times the approximately 8 microL/min determined from the tracer appearance rate in blood (Cl). The fractional contribution of tissues bordering the peritoneal cavity to the overall Cl was determined to be diaphragm, 55%; viscera, 30%; and abdominal wall, 15%. The present study determines whether direct measurement of visceral peritoneal lymph flow matches the 30% (approximately 2.5 microL/min) contribution of the visceral peritoneal lymph flow as measured indirectly by the Cl method. The mesenteric lymph duct that exclusively drains lymph from the gut, liver, and mesentery was cannulated in 15 rats, and lymph flow from the duct was collected at hourly intervals up to 6 hours under near-normal physiologic conditions and under conditions of simulated PD. Changes in mesenteric lymph flow that resulted from a challenge with 3 mL intravenous saline were captured using real-time video. We observed no significant differences between the hourly lymph volumes collected over 6 hours in naïve animals (n = 5, p > 0.05). Under conditions of simulated PD with dialysis fluid in the peritoneal cavity, the mesenteric duct lymph flow averaged 8.67 +/- 1.41 microL/min (n = 10). That flow is similar to reported data on total peritoneal Cl in rats; and 4 times the 2.5 microL/min visceral peritoneal contribution to the total peritoneal Cl. The intravenous saline challenge significantly increased mesenteric lymph duct output to 30.9 +/- 1.6 microL/min (n = 5, p < 0.01) and reduced the lymph-to-plasma concentration ratio (L/P) by 43%. The reflection coefficient for total proteins (sigma(prot)) across the intestinal capillaries as calculated from the filtration rate-dependent L/P ratio when the transcapillary fluid escape rate and the mesenteric lymph flow were both high was more than 0.87. We concluded that (A) under near-normal physiologic conditions, the mesenteric lymph duct flow is steady, but quite low; (B) under conditions of simulated PD, the mesenteric lymph duct flow increases significantly from the physiologic norm; (C) mesenteric lymph duct flow is sensitive to the peritoneal fill volume; (D) during simulated PD, the fractional visceral peritoneal lymph flow measured indirectly from plasma appearance of intraperitoneal tracer underestimates the directly measured mesenteric duct lymph flow; and (E) the increased transcapillary fluid escape rate is rapidly buffered by augmentation of mesenteric lymph duct output.

Chronic infusion of sterile peritoneal dialysis solution abrogates enhanced peritoneal gene expression responses to chronic peritoneal catheter presence

Chronic exposure to sterile peritoneal dialysis (PD) solutions is associated with microvascular and interstitial changes within the blood-peritoneal barrier (peritoneum). These changes are commonly linked to loss of peritoneal function over time, presumably because of angiogenesis-related increased vascular area. However, the effects on peritoneal microvascular function of chronic peritoneal exposure to PD solutions are unknown. The present study examined peritoneal microvascular function after chronic exposure to sterile PD solution. Six rats underwent permanent catheter insertion under anesthesia. Three rats were treated with approximately 16 mL conventional PD solution daily for 6 weeks; catheter insertion controls received 1 mL saline daily. At 6 weeks, visceral peritoneal microvascular function was assessed in vivo using intravital microscopy. Endothelial cell functions were assessed using messenger RNA (mRNA) gene microarray analysis. In both groups, significant angiogenesis was seen, predominantly in the base of the mesentery. Sensitivity and reactivity of the intestinal visceral peritoneal pre-capillary arterioles (A3 arterioles, 8 - 15 microm in diameter) were decreased in the catheter controls, but not in the chronic PD infusion rats. Chronic catheter presence increased the expression of 18 genes in the controls as compared with 12 genes in the chronic infusion rats. In both groups, expression of fibronectin, integrin-beta, integrin-alpha5, collagen type XVIII-alpha1, and matrix metalloproteinase was enhanced. Endothelial expression of proinflammatory genes (interleukin-1beta, tissue pathway inhibitor, chemokine ligand 2) was enhanced by chronic catheter insertion, but not after chronic PD fluid infusion. Increased expression of genes encoding proteins involved in inflammation and tissue remodeling results from peritoneal catheter-related endothelial cell activation. Chronic exposure of the nonuremic peritoneum to sterile PD solutions overrides the catheter-related endothelial cell proinflammatory phenotype to restore peritoneal microvascular function.

Cellular edema regulates tissue capillary perfusion after hemorrhage resuscitation

BACKGROUND

Hemorrhage-induced activation of endothelial cell Na+/H+ -exchanger results in cellular swelling, which physically impedes capillary filling and compromises gut perfusion. We hypothesized that correction of the vascular volume deficit by conventional resuscitation does not improve capillary filling unless cellular swelling is prevented. Also, we hypothesized that adjunctive direct peritoneal resuscitation (DPR) with topical peritoneal dialysis solution (Delflex; Fresenius USA, Inc., Ogden, Ut) enhances capillary filling and gut perfusion by mechanisms that are independent of the Na+/H+ function.

METHODS

In vivo intravital videomicroscopy and Doppler velocimeter were used by us to measure microvascular diameter and flow, capillary filling (index of functional capillary density, FCD), and endothelial cell function in the terminal ileum of anesthetized rats. Rats were bled to 50% mean arterial pressure for 60 min and resuscitated with the shed blood plus 2 volumes of saline (conventional resuscitation). Prevention of endothelial cell swelling was achieved with topical amiloride (specific Na+/H+ inhibitor) in the tissue bath before hemorrhage or simultaneously with conventional resuscitation. DPR was simulated by instillation of Delflex in the tissue bath as adjunctive to conventional resuscitation. Sham no hemorrhage group and a simulated DPR group that received topical amiloride treatment served as controls.

RESULTS

Conventional resuscitation from hemorrhagic shock restored and maintained central hemodynamics but caused progressive and persistent intestinal vasoconstriction and hypoperfusion associated with low FCD and endothelial cell dysfunction. Prevention of endothelial cell swelling when combined with conventional resuscitation, preserved endothelial cell function, and restored local intestinal microvascular variables to near-prehemorrhage levels. Simulated adjunctive DPR produced rapid, sustained, and generalized vasodilation associated with restoration of endothelial cell function, and maximum recruitment of FCD independent of the Na+/H+ -exchanger function.

CONCLUSIONS

Paradoxical endothelial cell swelling occurs early during hemorrhagic shock because of activation of the Na+/H+ exchanger. This cellular edema, which is not resolved by correction of the vascular volume deficit, explains the persistent postresuscitation endothelial cell dysfunction and gut hypoperfusion. Simulated adjunctive DPR in this study reversed endothelial cell swelling and enhanced gut perfusion by mechanisms that are independent of the Na+/H+ exchanger activity.

Role of Adenosine Receptor Subtypes in Rat Jejunum in Unfed State Versus Glucose-Induced Hyperemia

BACKGROUND

Adenosine is a key mediator in intestinal absorptive hyperemia. This study examines the role of adenosine receptor subtypes in the intestinal microvasculature at rest (unfed) and during glucose exposure.

MATERIALS AND METHODS

Intravital video microscopy was used to record vascular responses in the rat jejunum in unfed resting states versus active glucose absorption. Two series of experiments were performed: topical adenosine alone and with adenosine receptor antagonists, and topical glucose alone and with adenosine receptor antagonists.

RESULTS

We found that distal premucosal arterioles were more reactive to adenosine than were larger inflow arterioles. The selective A1 adenosine receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) (200 nm), and the A2b receptor antagonist, alloxazine (60 microm), decreased the sensitivity and reactivity of the inflow and premucosal arterioles to adenosine, whereas the selective A2a receptor antagonist 8-(3-chlorostyryl)caffeine (CSC) (200 nm) had no effect on inflow arteriole diameter and only slightly reduced the premucosal arteriolar sensitivity to adenosine. As previously observed, isotonic glucose caused vasodilation (24 +/- 3.4% of the control) in the distal premucosal arterioles. Conversely, premucosal arterioles did not dilate during exposure of the intestine to isotonic mannitol solution that is not actively absorbed. Adenosine A2a RA CSC and A2b RA alloxazine attenuated glucose-induced vasodilation, whereas adenosine A1 RA DPCPX completely abolished glucose-induced dilation.

CONCLUSIONS

These findings suggest that resting tone in premucosal vessels appears to be responsive to adenosine mediation rather than inflow arteriolar tone; the adenosine A1, A2a, and A2b receptors all contribute to adenosine-mediated vasodilation in the intestine, with the greatest attenuation seen with A1 receptor antagonism; and other vasoactive mediators might also contribute to glucose-induced jejunal vasodilation, and interaction might exist between adenosine receptors and other mediators.

Immune-enhancing diet and cytokine expression during chronic sepsis: an immune-enhancing diet containing L-arginine, fish oil, and RNA fragments promotes intestinal cytokine expression during chronic sepsis in rats

Chronic feeding with enteral immune-enhancing diets (IEDs) provides benefits based on composition of the diet, route of feeding, and timing of feeding in relation to timing of trauma or surgery. Our prior studies of acute feeding in naïve rats demonstrated that IED promotes blood flow and proinflammatory cytokines in the ileum. We hypothesized that chronic feeding with IED would shift gut immune status to an anti-inflammatory state during chronic sepsis, resulting in an altered state of cytokine expression in the gut. Five days prior to feeding, gauze was implanted subcutaneously in the backs of male Sprague-Dawley rats, which were fed for 3 days with either control diet (CD, Boost; Mead-Johnson, Evansville, IL) or IED (Impact; Novartis) and randomly assigned to one of four groups: saline control (NS) + control diet (CD), sepsis (EC) + CD, NS + IED, or EC + IED. EC rats were inoculated with 10(9) CFU Escherichia coli and 10(9) CFU Bacteroides fragilis in 2 ml normal saline into the back sponge while NS rats received 2 mL normal saline alone. After 3 days, animals were anesthetized and gut tissue samples were harvested and frozen at -80 degrees C. Tissue protein was extracted and ELISA was performed for interleukin (IL-1beta, IL-5, IL-6, IL-10, tumor necrosis factor (TNF)-alpha, and interferon (IFN)-gamma. In saline controls, IED feeding decreased IL-1beta, IL-5, IL-6, TNF-alpha, and IFN-gamma and increased IL-10 compared with CD-fed animals. In septic animals, IED feeding increased IL-5 and IL-6, while decreasing IFN-gamma and IL-10 in the distal third of the small intestine compared with CD-fed septic rats, whereas IL-1beta and TNF-alpha levels were unchanged. Chronic IED feeding produced a anti-inflammatory state via decreased IFN-gamma and increased IL-5 and IL-6, which both promote gut IgA class switching, suggesting that the gut is shifted toward humoral immunity during chronic IED feeding in septic rats.

Poor validity of residual volumes as a marker for risk of aspiration in critically ill patients

BACKGROUND AND AIMS

Elevated residual volumes (RV), considered a marker for the risk of aspiration, are used to regulate the delivery of enteral tube feeding. We designed this prospective study to validate such use.

METHODS

Critically ill patients undergoing mechanical ventilation in the medical, coronary, or surgical intensive care units in a university-based tertiary care hospital, placed on intragastric enteral tube feeding through nasogastric or percutaneous endoscopic gastrostomy tubes, were included in this study. Patients were fed Probalance (Nestle USA) to provide 25 kcal/kg per day (to which 10 yellow microscopic beads and 4.5 mL of blue food coloring per 1,500 mL was added). Patients were randomized to one of two groups based on management of RV: cessation of enteral tube feeding for RV >400 mL in study patients or for RV >200 mL in controls. Acute Physiology and Chronic Health Evaluation (APACHE) III, bowel function score, and aspiration risk score were determined. Bedside evaluations were done every 4 hrs for 3 days to measure RV, to detect blue food coloring, to check patient position, and to collect secretions from the trachea and oropharynx. Aspiration/regurgitation events were defined by the detection of yellow color in tracheal/oropharyngeal samples by fluorometry. Analysis was done by analysis of variance, Spearman's correlation, Student's t-test, Tukey's method, and Cochran-Armitage test.

RESULTS

Forty patients (mean age, 44.6 yrs; range, 18-88 yrs; 70% male; mean APACHE III score, 40.9 [range, 12-85]) were evaluated (21 on nasogastric, 19 on percutaneous endoscopic gastrostomy feeds) and entered into the study. Based on 1,118 samples (531 oral, 587 tracheal), the mean frequency of regurgitation per patient was 31.3% (range, 0% to 94%), with a mean RV for all regurgitation events of 35.1 mL (range, 0-700 mL). The mean frequency of aspiration per patient was 22.1% (range, 0% to 94%), with a mean RV for all aspiration events of 30.6 mL (range, 0-700 mL). The median RV for both regurgitation and aspiration events was 5 mL. Over a wide range of RV, increasing from 0 mL to >400 mL, the frequency of regurgitation and aspiration did not change appreciably. Aspiration risk and bowel function scores did not correlate with the incidence of aspiration or regurgitation. Blue food coloring was detected on only three of the 1,118 (0.27%) samples. RV was < or =50 mL on 84.1% and >400 mL on 1.4% of bedside evaluations. Sensitivities for detecting aspiration per designated RV were as follows: 400 mL = 1.5%; 300 mL = 2.3%; 200 mL = 3.0%; and 150 mL = 4.5%. Low RV did not assure the absence of events, because the frequency of aspiration was 23.0% when RV was <150 mL. Raising the designated RV for cessation of enteral tube feeding from 200 mL to 400 mL did not increase the risk, because the frequency of aspiration was no different between controls (21.6%) and study patients (22.6%). The frequency of regurgitation was significantly less for patients with percutaneous endoscopic gastrostomy tubes compared with those with nasogastric tubes (20.3% vs. 40.7%, respectively; p = .046). There was no correlation between the incidence of pneumonia and the frequency of regurgitation or aspiration.

CONCLUSIONS

Blue food coloring should not be used as a clinical monitor. Converting nasogastric tubes to percutaneous endoscopic gastrostomy tubes may be a successful strategy to reduce the risk of aspiration. No appropriate designated RV level to identify aspiration could be derived as a result of poor sensitivity over a wide range of RV. Study results do not support the conventional use of RV as a marker for the risk of aspiration.

Intravital intestinal videomicroscopy: Techniques and experiences

Intravital videomicroscopy (IVM) of the gastrointestinal (GI) tract is a sophisticated and powerful technique to directly observe the neurologically intact microvasculature of rats in naive and pathological conditions. We combine IVM with other techniques (i.e., vascular ring tension analysis and colorimetric microsphere determination of whole organ blood flow) to develop a strategy for the systematic analysis of the regulation of GI blood flow in healthy animals and in models of systemic sepsis and resuscitated hemorrhagic shock. We also study the molecular biology of the GI tract (enzyme- or radio-linked immunosorbent assays, fluorescent Greiss assay, and immunoblots) to correlate expression and levels of vascular mediators in tissue and arterial, venous, and portal blood with functional activity of the GI microvascular tree. When combined, these techniques develop a picture of gut pathophysiology at the level of the endothelium, vascular smooth muscle cells, and blood cells in the microcirculation. Our work led us to the general hypothesis that altered microcirculatory function in disease states lies primarily at the level of the interface between vascular and tissue physiology, i.e., the endothelial cell. This review focuses on methods and techniques for studying microvascular function, and concludes with focused reviews of pertinent findings.

Microvascular responses to adenosine help explain functional and pathologic differences between intestinal segments

BACKGROUND

Many physiologic (post-prandial hyperemia), pathologic (inflammatory bowel disease), and clinical (enteral feeding) phenomena involve changes in microvascular blood flow to the intestine. Adenosine (Ado) derived from energy metabolism causes vasodilation and appears to be involved in some of these events. The Ado-mediated control mechanisms appear to vary with the diameter of the microvessels and the function of the tissue. This suggests the possibility that Ado-based microvascular control varies between anatomic intestinal segments and microvascular levels in those intestinal segments.

METHODS

In vivo digital intravital microscopy was used to measure the responses of larger distributing (A1) and smaller premucosal (A3) vessels to Ado in intact neurovascular loops of jejunum and terminal ileum of the rat. Dose-response curves to Ado were determined.

RESULTS

Microvascular dilation and augmented blood flow to Ado were significantly greater in the jejunum than in the terminal ileum. Ado-induced dilation was greater in the smaller A3 than in the larger A1 microvessels.

DISCUSSION

These data indicate (1) different vasodilator mechanisms for the jejunum and the terminal ileum, (2) a greater role for Ado-related microvascular control in the jejunum compared with the ileum, and (3) a greater Ado-related control in the premucosal (A3) vessels. These findings suggest that Ado-mediated microvascular effects could explain why some clinical phenomena vary in intensity in selective intestinal segments, and are likely to involve different microvascular control mechanisms in the different segments. Knowledge of these Ado mechanisms could be beneficial in certain clinical scenarios to control blood flow during pathologic conditions.

A novel method of peritoneal resuscitation improves organ perfusion after hemorrhagic shock

BACKGROUND

After resuscitation from hemorrhagic shock, intestinal microvessels constrict leading to impairment of blood flow. This occurs despite restoration and maintenance of central hemodynamics. Our recent studies have demonstrated that topical and continuous exposure of the gut microvasculature to a clinical solution (Delflex; Fresenius Medical Care), as a technique of direct peritoneal resuscitation (DPR), reverses the postresuscitation vasoconstriction and hypoperfusion to a sustained dilation and hyperperfusion. We hypothesize that initiation of DPR simultaneously with resuscitation from hemorrhagic shock enhance organ blood flow to all tissues surrounding the peritoneal cavity as well as distant organs.

METHODS

Male Sprague-Dawley rats were anesthetized, intubated and cannulated for monitoring of hemodynamics and for withdrawal of blood. Rats were hemorrhaged to 50% of mean blood pressure for 60 minutes prior to resuscitation with shed blood plus 2 volumes of saline. Animals were randomized for intraperitoneal therapy with 30 mL saline (group 1, n = 9), or Delflex (group 2, n = 9). Whole organ blood flow was measured by colorimetric microsphere technique with phantom organ at baseline, after completion of resuscitation, and at 120 minutes postresuscitation. Replenishment of the dwelling intraperitoneal saline or Delflex was performed in (group 3, n = 8), and (group 4, n = 8), respectively at 90 minutes postresuscitation, and a single whole organ blood flow was performed at 120 minutes postresuscitation.

RESULTS

Direct peritoneal resuscitation caused a significant increase in blood flow to the jejunum (35%), ileum (33%), spleen (48%), and pancreas (57%), whereas a marked increase in blood flow was detected in the lung (111%), psoas major muscle (115%), and diaphragm (132%), as compared with the saline treated animals in group 1. At 120 minutes postresuscitation, organ blood flow returned to the prehemorrhagic shock baseline level in all organs irrespective of peritoneal therapy. Replenishment of the intraperitoneal solution in group 3 and 4, enhanced blood flow to the liver, kidneys, and diaphragm.

CONCLUSIONS

Direct peritoneal resuscitation enhanced blood flow to organs incited in the pathogenesis of multiple organ failure that follows hemorrhagic shock.

Adrenomedullin is increased in the portal circulation during chronic sepsis in rats

BACKGROUND

A clinical hallmark of sepsis is an early, hyperdynamic cardiac phase (increased cardiac output) that degrades to a hypodynamic phase, which results in poor gut perfusion and subsequent gastrointestinal (GI) hypoxemia, tissue ischemia, necrosis and loss of gut barrier function. Studies in rat cecal-ligation and puncture suggest that the potent vasodilator adrenomedullin (AM) might initiate or maintain the hypodynamic phase. We hypothesize that AM expression is increased in acute Escherichia coli bacteremia and chronic E coli-Bacteroides fragilis sepsis.

METHODS

Acute bacteremia: male Sprague-Dawley rats were anesthetized (urethane/alpha-chloralose), tracheotomized, and cannulated for monitoring blood pressure (MABP) and heart rate (HR) and for infusion of E coli (10(9) colony-forming units [CFU] E coli per 1 mL normal saline) and blood sampling. Arterial blood was withdrawn for arterial blood gas (ABG) measurements every 60 minutes. After 6 hours, we harvested lung, liver, kidney, spleen, and small intestine tissue samples and drew arterial and portal blood for AM enzyme-linked immunosorbent assay (ELISA). Chronic sepsis: a sterile gauze pad was implanted and animals recovered for 5 days. Twenty-four hours (10(9) CFU E coli and 10(9) CFU B fragilis per 1 mL normal saline; 1 injection) or 72 hours (2 injections) after the inoculation of the back sponge, rats were anesthetized, intubated, and cannulated as above. MABP, HR, and ABG were measured for 1 hour before tissue and serum harvest for AM ELISA.

RESULTS

Sepsis increased HR and MABP in all groups. Acute sepsis caused a respiratory alkalosis and pH was also elevated in chronic sepsis. Serum AM levels were increased in all groups compared with baseline and remained elevated at every time point, but were not different between saline controls and septic animals at any time point, except for the portal serum from the 72-hour chronic sepsis, which was elevated.

CONCLUSIONS

These data suggest that surgical manipulation alone is sufficient to stimulate AM secretion, most probably from endothelial cells. While the AM levels were decreasing at 72 hours compared with 6 hours or 24 hours in the arterial blood and the saline control portal blood, it remained elevated in the septic portal samples, suggesting that the sepsis-induced increase of AM was derived from the gut by a different mechanism than that which elevated arterial serum levels.

Tempol, an antioxidant, restores endothelium-derived hyperpolarizing factor-mediated vasodilation during hypertension

Acetylcholine releases a non-prostanoid endothelium-derived hyperpolarizing factor (EDHF) and nitric oxide from physiological salt solution perfused rat mesenteric arteries. This study reports an impairment in EDHF-mediated vasodilation in deoxycorticosterone acetate (DOCA)-salt hypertensive versus control normotensive rats. Nitric oxide-mediated vasodilation to acetylcholine was not altered in the animals. We hypothesize that free radical species generated as by-products of arachidonic acid metabolism contribute to impaired EDHF-mediated dilation in DOCA-salt hypertension. With or without reduced nicotinamide adenine dinucleotide phosphate (NADPH) as co-factor, arterial microsomes generate free radical species upon incubation with arachidonic acid. The production of free radicals was significantly higher in DOCA-salt versus control rat microsomes, and was totally eliminated by addition of cyclooxygenase-2 inhibitors NS-398 or celecoxib at 30 microM. Treatment of DOCA-salt rats with tempol (an antioxidant; 15 mg/kg, i.p., 21 days) alleviates hypertension; improves acetylcholine-induced EDHF-mediated vasodilation in DOCA-salt rats, and decreases arachidonic acid-driven microsomal free radical production. Serum level of 8-isoprostanes is elevated in DOCA-salt hypertension versus control or sham-salt rats, and the increase was reversed by tempol treatment. These results show that EDHF-mediated dilation of rat mesenteric arteries is impaired in DOCA-salt induced hypertension. Our data also suggest that cyclooxygenase-2 mediates free radical production, and that free radicals modulate the EDHF-mediated vascular response in DOCA-salt induced hypertension.

Intraperitoneal resuscitation improves intestinal blood flow following hemorrhagic shock

OBJECTIVE

To study the effects of peritoneal resuscitation from hemorrhagic shock.

SUMMARY BACKGROUND DATA

Methods for conventional resuscitation (CR) from hemorrhagic shock (HS) often fail to restore adequate intestinal blood flow, and intestinal ischemia has been implicated in the activation of the inflammatory response. There is clinical evidence that intestinal hypoperfusion is a major factor in progressive organ failure following HS. This study presents a novel technique of peritoneal resuscitation (PR) that improves visceral perfusion.

METHODS

Male Sprague-Dawley rats were bled to 50% of baseline mean arterial pressure (MAP) and resuscitated with shed blood plus 2 equal volumes of saline (CR). Groups were 1) sham, 2) HS + CR, and 3) HS + CR + PR with a hyperosmolar dextrose-based solution (Delflex 2.5%). Groups 1 and 2 had normal saline PR. In vivo videomicroscopy and Doppler velocimetry were used to assess terminal ileal microvascular blood flow. Endothelial cell function was assessed by the endothelium-dependent vasodilator acetylcholine.

RESULTS

Despite restored heart rate and MAP to baseline values, CR animals developed a progressive intestinal vasoconstriction and tissue hypoperfusion compared to baseline flow. PR induced an immediate and sustained vasodilation compared to baseline and a marked increase in average intestinal blood flow during the entire 2-hour post-resuscitation period. Endothelial-dependent dilator function was preserved with PR.

CONCLUSIONS

Despite the restoration of MAP with blood and saline infusions, progressive vasoconstriction and compromised intestinal blood flow occurs following HS/CR. Hyperosmolar PR during CR maintains intestinal blood flow and endothelial function. This is thought to be a direct effect of hyperosmolar solutions on the visceral microvessels. The addition of PR to a CR protocol prevents the splanchnic ischemia that initiates systemic inflammation.

Immune-enhancing enteral diet increases blood flow and proinflammatory cytokines in the rat ileum

BACKGROUND

Enteral feeding improves outcome following surgery. Benefits depend on timing, route (enteral vs parenteral), and nutrient composition (standard vs immune-enhancing diets; IED). IED augments intestinal immunity and stimulates gut blood flow during absorption in a nutrient-specific manner. We hypothesize that a mechanism for the gut protective effect of IED is augmentation of blood flow to the gut-associated lymphoid tissue (GALT) in the terminal ileum.

METHODS

Male Sprague-Dawley rats (200-230 g) were fed for 5 days either an IED (Impact, Novartis) or an isocaloric, isonitrogenous control diet (CD, Boost, Mead-Johnson) matched to the daily caloric intake (rat chow). Rats were then anesthetized and cannulated for microsphere determination of whole organ blood flow. Blood glucose levels and blood flow to abdominal organs were determined at baseline and 30, 60, 90, and 120 min after gastric gavage (2 ml) with IED or CD. Intestinal tissues were harvested for cytokine levels (ELISA: IL-4, IL-10, IFN-gamma, and IgA).

RESULTS

Chronic IED increased baseline blood flow in the distal third of the small intestine compared to chow-fed and CD. Baseline blood flow was comparable between IED and CD in all other organs. CD and IED produced different blood flow patterns after gavage. CD increased blood flow compared to baseline and IED in antrum, duodenum, and jejunum. Ileal blood flow remained elevated in IED rats for 2 h, perhaps suggesting maximal blood flow. IED increased blood glucose compared to CD. Chronic IED increased IL-4 and decreased IL-10 in the terminal ileum.

CONCLUSIONS

Chronic IED exposure increases and sustains ileal blood flow compared to CD with altered proinflammatory cytokine expression. Our data suggest that a mechanism for the IED effect involves the selective perfusion of the terminal ileum and contiguous GALT during IED nutrient absorption.

Omega-3 fatty acids in immune-enhancing enteral diets selectively increase blood flow to the ileum by a bile acid dependent mechanism

BACKGROUND

The immune-enhancing diet (IED) (Impact, Novartis Corp, Minneapolis, Minn) initiates a delayed and sustained increase in blood flow to the ileum and gut-associated lymphoid tissue. The immune-enhancing benefits of Impact (Novartis Corp) are attributed to the addition of L-arginine, fish oil (FO), and RNA fragments to a standard enteral diet. The sustained increase in blood flow to the gut-associated lymphoid tissue during IED exposure might account for these immune effects. We hypothesized that the increase in ileal blood flow with IED might be a result of ileal omega-3 fatty acid absorption in the ileum by a bile-dependent mechanism.

METHODS

Male Sprague-Dawley rats (200 g-230 g) were anesthetized and cannulated for microsphere measurement of whole organ blood flow. Rats received gastric gavage (2 mL) with either IED, an isocaloric, isonitrogenous control diet (CD) (Boost, Mead-Johnson, Evansville, Ind), CD plus menhaden FO (CD+FO), or CD+FO plus bile duct ligation (BDL). Blood flow was determined at baseline and 30, 60, and 120 minutes after short-term gavage.

RESULTS

Baseline blood flow and central hemodynamics were comparable in all groups. In the ileum, at 120 minutes postgavage, blood flow was increased by IED and CD+FO compared with baseline and CD. BDL prevented the increase in blood flow in the CD+FO+BDL rats. All groups exhibited differences in splanchnic blood flow distribution after gavage: CD and CD+FO+BDL increased blood flow compared with baseline early in the proximal gut and spleen. IED and CD+FO produced a delayed, sustained hyperemia to the distal gut.

CONCLUSIONS

Gastrointestinal blood flow distribution after feeding is dependent on nutrient composition. These findings suggest that omega-3 fatty acids are the components of the enteral IED, Impact (Novartis Corp), which produce the increased blood flow to the terminal ileum and its contiguous gut-associated lymphoid tissue. Our data suggests that an intact enterohepatic bile pathway is needed for the IED blood flow effect.

Immune-enhancing enteral diet selectively augments ileal blood flow in the rat

BACKGROUND

Clinical studies show that immune-enhancing enteral diets (IED; with L-arginine, fish oil, and RNA fragments) decrease the rate of sepsis and shorten the length of hospital stay after the start of enteral feeding. These beneficial effects are dependent on the route of administration (enteral vs parenteral) and on the nutrient composition (IED vs standard diets). Gut exposure to an IED seems to preserve and/or augment intestinal mucosal immunity. However, nutrient absorption stimulates gut blood flow in a nutrient-specific manner (i.e., postprandial hyperemia). We hypothesized that an IED would initiate a different pattern of whole organ blood flow compared to a standard diet. This suggests that a mechanism for the protective effect of IED might be the preferential augmentation of gut blood flow to gut-associated lymphoid tissue (GALT) or mucosa-associated lymphoid tissue (MALT).

METHODS

Male Sprague-Dawley rats (200-225 g) were anesthetized and cannulated for colorimetric microsphere determination of blood flow distribution (with the phantom organ technique). Animals received gastric gavage (2 ml) of an IED (Impact; Novartis) or an isocaloric, isonitrogenous control diet (Boost; Mead-Johnson). Blood flow to the antrum, duodenum, jejunum, ileum, colon, liver, kidneys, and spleen was determined at baseline and 30, 60, 90, and 120 min after gavage.

RESULTS

Baseline blood flows to the left and right kidneys were within 10%, indicating the technical integrity of the microsphere technique and assay. Control diet augmented blood flow compared to IED in the antrum, duodenum, jejunum, and spleen. Conversely, IED gavage stimulated a delayed and sustained hyperemic response in the ileum. IED also increased hepatic blood flow early (30 min). IED increased blood glucose levels compared to control diet at 30, 60, and 90 min, suggesting enhanced nutrient absorption.

CONCLUSIONS

These data show that blood flow distribution depends on nutrient composition and that IED preferentially augments blood flow to the ileum. Since the terminal jejunum and ileum contain much of the GALT, our data suggest that a mechanism for enterally stimulated mucosal immunity involves selective perfusion of the terminal ileum during IED nutrient absorption.

Hypercoagulability in patients with obstructive sleep apnea

BACKGROUND

Obstructive sleep apnea (OSA) has been linked to cardiovascular complications such as stroke and myocardial infarction. Previous studies demonstrate that OSA patients show elevated fibrinogen levels and increased platelet aggregation that are reversed with 1 night of nasal continuous positive airway pressure treatment (NCPAP). Questioning overall coagulability in OSA, we examined whole blood coagulability in 11 chronically NCPAP treated OSA subjects, 22 previously untreated OSA subjects, and in 16 of these after 1 night of NCPAP treatment.

PATIENTS AND METHODS

During full polysomnography, subjects from each group had blood drawn prior to bedtime (21:00 h) and upon waking in the morning (07:00 h).

RESULTS

Untreated OSA patients had faster P.M. clotting times than chronically treated OSA patients (3.33+/-0.31 versus 6.12+/- 0.66 min, P<0.05 by ANOVA). A.M. values showed similar results (4.31+/- 0.34 min versus 7.08+/-0.52 min, P<0.05 by ANOVA) for the respective groups. One overnight treatment with nasal CPAP did not produce a significant change in A.M. whole blood coagulability (4.35 +/-0.43 to 5.31+/-0.53 min; n=16; P=0.1) in 16 treated subjects.

CONCLUSIONS

These data indicate a relationship between obstructive sleep apnea and blood hypercoagulability status that appears to be reversed by chronic NCPAP treatment. These data suggest that NCPAP might protect against the development of cardiovascular complications in OSA patients.