Jejunal luminal nitric oxide during severe hypovolemia and sepsis in anesthetized pigs

Influences of Vagotomy on Gut Ischemia-Reperfusion Injury in Mice

BACKGROUND

How vagotomy affects host responses to gut ischemia-reperfusion (I/R) is unclear.

MATERIALS AND METHODS

Experiment 1: male Institute of Cancer Research mice (n = 22) were assigned to the I/R or the vago-I/R group. The I/R mice underwent 45-min superior mesenteric artery (SMA) occlusion. The vago-I/R mice received vagotomy before SMA occlusion. Survival was observed for 48 h.Experiment 2: mice (n = 55) were divided into four groups (Sham, vago, I/R, vago-I/R). Sham and vago groups did not undergo gut I/R. Mice were killed at 3 or 6 h after reperfusion, and cytokine levels in the plasma, jejunum, and ileum were evaluated. In addition, gut histology at 6 h was examined.Experiment 3: mice (n = 24) were divided into four groups as in Experiment 2. The small intestine was harvested at 3 h after reperfusion and the tissue was cultured ex vivo for 3 h. Cytokine levels of the culture supernatant were then measured.

RESULTS

Experiment 1: survival was significantly worse with vago-I/R than I/R.Experiment 2: along with severe gut injury, vago-I/R increased IL-6 and monocyte chemoattractant protein-1 (MCP-1) in plasma, IFN-γ in the jejunum and MCP-1 in the ileum, as compared with I/R. Significant positive correlations were noted between plasma and intestinal levels of pro-inflammatory cytokines (IL-6, MCP-1, and TNF-α).Experiment 3: MCP-1 in the jejunal culture medium was higher in the vago-I/R than in the I/R group.

CONCLUSIONS

Vagotomy worsens survival after gut I/R, together with increases in pro-inflammatory cytokines in both plasma and the gut in association with severe intestinal tissue damage.

Tissue bioenergetics and microvascular perfusion are impaired in rat ileal mucosa in normotensive sepsis

OBJECTIVE

Sepsis is a systemic inflammatory response to a bacterial infection. Inflammation may result in injury to the small bowel and an increase in translocation of bacteria and toxins across the mucosal barrier, which may contribute to the progression of sepsis. Microcirculatory perfusion or cytopathic hypoxia may cause impairment of tissue bioenergetics and injury in sepsis. The objective of this study was to determine if sepsis is associated with microcirculatory hypoperfusion and impaired tissue bioenergetics in the ileal mucosa.

MATERIALS AND METHODS

Sprague-Dawley rats were randomized to cecal ligation and perforation (sepsis group, n = 12) or control group (n = 14) and received arterial and venous catheters and fluid resuscitation. Following 24 h, rats were anesthetized with isoflurane and the ileum was prepared for intravital microscopy. Images of NADH fluorescence, which is an index of tissue bioenergetics, central arterial diameter, red cell velocity, red cell flux, and average intercapillary area, were recorded in 6-9 villi in each rat.

RESULTS

Central arterial red cell flux (control 277 +/- 30 cell/s, sepsis 108 +/- 13 cells/s, p < .05), diameter (control 10.4 +/- 0.4 microm, sepsis 8.2 +/- 0.3 microm, p < .05) and red cell velocity (control 590 +/- 47 microm/s, sepsis 449 +/- 63 microm/s, p < .05) were decreased while average intercapillary area (control 815 +/- 171 microm(2), sepsis 1412 +/- 364 microm(2), p < .05) and NADH fluorescence (control 116 +/- 6 AIU, sepsis 154 +/- 9 AIU, p < .05) were increased at the villus tip in the sepsis group.

CONCLUSION

Sepsis is associated with bioenergetic impairment and capillary hypoperfusion at the villus tip and a decrease in red cell flux in the central arteriole.

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Nitric oxide synthase inhibition in sepsis? Lessons learned from large-animal studies

Nitric Oxide (NO) plays a controversial role in the pathophysiology of sepsis and septic shock. Its vasodilatory effects are well known, but it also has pro- and antiinflammatory properties, assumes crucial importance in antimicrobial host defense, may act as an oxidant as well as an antioxidant, and is said to be a "vital poison" for the immune and inflammatory network. Large amounts of NO and peroxynitrite are responsible for hypotension, vasoplegia, cellular suffocation, apoptosis, lactic acidosis, and ultimately multiorgan failure. Therefore, NO synthase (NOS) inhibitors were developed to reverse the deleterious effects of NO. Studies using these compounds have not met with uniform success however, and a trial using the nonselective NOS inhibitor N(G)-methyl-l-arginine hydrochloride was terminated prematurely because of increased mortality in the treatment arm despite improved shock resolution. Thus, the issue of NOS inhibition in sepsis remains a matter of debate. Several publications have emphasized the differences concerning clinical applicability of data obtained from unresuscitated, hypodynamic rodent models using a pretreatment approach versus resuscitated, hyperdynamic models in high-order species using posttreatment approaches. Therefore, the present review focuses on clinically relevant large-animal studies of endotoxin or living bacteria-induced, hyperdynamic models of sepsis that integrate standard day-to-day care resuscitative measures.

Candesartan improves survival following severe hypovolemia in pigs; a role for the angiotensin II type 2 receptor?

OBJECTIVE

To investigate the involvement of intestinal angiotensin II type 2 receptors in the outcome of acute severe hypovolemia as well as systemic and regional mesenteric hemodynamics and intestinal mucosal functions in anesthetized pigs.

DESIGN AND SETTING

Prospective, interventional animal study in a university research laboratory.

SUBJECTS

53 landrace pigs, 28-35 kg.

INTERVENTIONS

30+30% or 20+20% hemorrhage of estimated total blood volume followed by retransfusion performed in untreated controls, in animals treated with the angiotensin II type 1 receptor blocker candesartan or with a combination of candesartan and the angiotensin II type 2 receptor blocker PD123319.

MEASUREMENTS AND RESULTS

Following 30+30% hemorrhage the candesartan-treated animals attained a significantly higher survival rate than controls and animals treated with PD123319 in combination with candesartan. Less pronounced hemorrhage (20+20%) resulted in no mortality and functional variables were assessed. A significantly higher output of jejunal intraluminal nitric oxide occurred during hypovolemia in the candesartan treated group than in controls and animals that received PD123319 in combination with candesartan. Jejunal transmucosal potential difference was significantly better preserved after retransfusion in candesartan-treated animals than in controls. Expression of angiotensin II type 2 receptors in intestinal tissue was significantly higher in animals surviving the 30+30% hemorrhage than in nonsurvivors.

CONCLUSIONS

Lethal circulatory failure is possibly influenced by use of angiotensin receptor ligands, and activation of intestinal angiotensin II type 2 receptors may play a significant role in improving the outcome of severe hypovolemia.

Role of intestine in postsurgical complications: involvement of free radicals

Surgery at any location in the body leads to surgical stress response and alterations in normal body homeostasis. The intestine is extremely sensitive to surgical stress even at remote locations and the gastrointestinal tract plays an important role in the development of postsurgical complications such as sepsis, the systemic immune response syndrome (SIRS), and multiple organ failure syndrome (MOFS). The generation of free radicals and subsequent biochemical alterations at the cellular and subcellular level in the intestine has been suggested to play an important role in this process. These oxidative stress-induced events in the mucosa might act as an initiator of distant organ damage and also facilitate bacterial adherence onto the epithelium and translocation into the systemic circulation. This review attempts to highlight the important role of intestine and oxygen free radicals in initiating post-surgical complications.

Gut mucosal damage during endotoxic shock is due to mechanisms other than gut ischemia

Whether the gut alterations seen during sepsis are caused by microcirculatory hypoxia or disturbances in cellular metabolic pathways associated with mitochondrial respiration remains controversial. We hypothesized that hypoperfusion or hypoxia and local production of nitric oxide might play an important role in the development of gut mucosal injury during endotoxic shock and investigated their roles by using differing levels of fluid resuscitation and occlusion of the superior mesenteric artery (SMA). Anesthetized New Zealand rabbits were allocated to group I (sham, n = 8); group II [low-dose endotoxin (LPS, Escherichia coli-055:B5, 150 microg/kg)/fluid resuscitation (12 ml x kg(-1) x h(-1)); n = 8]; group III [high-dose LPS (1 mg/kg)/fluid resuscitation (12 ml x kg(-1) x h(-1)); n = 8]; group IV [high-dose LPS (1 mg/kg)/hypovolemia (4 ml x kg-1 x h(-1) fluids); n = 8]; and group V [SMA ligation/fluid resuscitation (12 ml x kg(-1) x h(-1)); n = 4]. Luminal gut lactate concentrations and PCO2 gap increased in groups IV and V (P < 0.05), reflecting alterations in gut perfusion. Interestingly, significant histological alterations were observed in all LPS groups but not in group V. Blood and luminal gut nitrate/nitrite concentrations increased only in group IV. The mechanism of gut injury in endotoxic shock seems unrelated to hypoxia and release of nitric oxide. Gut dysfunction may occur as a result of so-called "cytopathic hypoxia."

Mesenteric hemodynamic response to circulatory shock

PURPOSE OF REVIEW

The mesenteric hemodynamic response to circulatory shock is substantial and asymmetrical; the vasoconstrictive response disproportionately affects the mesenteric organs. The cardiac output is sustained partially, at no cost in nutrient flow to the mesenteric organs, by vasoconstriction of the mesenteric veins, resulting in the "autotransfusion" of up to 30% of the circulating blood volume into the systemic circulation.

RECENT FINDINGS

Hemorrhagic or cardiogenic shock also results in decreased perfusion pressure, prompting selective vasoconstriction of the mesenteric arterioles to maintain perfusion pressure of the vital organs, here at the selective expense of the mesenteric organs. Septic shock may be associated with increased or decreased mesenteric blood flow but is characterized by increased oxygen consumption, exceeding the capability of mesenteric oxygen delivery.

SUMMARY

The response to any of these conditions can, variably and unpredictably, cause hemorrhagic gastric stress erosions, nonocclusive mesenteric ischemia of the small bowel, ischemic colitis, ischemic hepatitis, acalculous cholecystitis, and/or ischemic pancreatitis. Injury to the mesenteric organs can also initiate the systemic inflammatory response syndrome and, consequently, multiple organ failure.

Effect of estradiol administration on splanchnic perfusion after trauma-hemorrhage and sepsis

PURPOSE OF REVIEW

This review focuses on the latest mechanistic understanding of the effects of estradiol on the splanchnic circulation and the possibility of estradiol treatment as an adjunct for the treatment of trauma-hemorrhage and sepsis.

RECENT FINDINGS

Systemic hypotension induced by shock accompanies marked alterations in blood flow to various organs. Decreased splanchnic perfusion is frequently observed after insults, such as severe hemorrhage or sepsis, which leads to the destruction of the intestinal mucosal barrier and hepatic dysfunction. Studies suggest that estradiol acts as a facilitator of the intestinal blood flow via the increased production of nitric oxide, decreased production of vasoconstrictors, attenuated neutrophil adhesion, and decreased formation of oxygen free radicals.

SUMMARY

Trauma-hemorrhage results in decreased circulating blood volume. In contrast, sepsis is an inflammatory state mainly mediated by bacterial products. However, these divergent insults show similar pathophysiologic alterations in terms of the splanchnic circulation. Because estradiol effectively protects the organs from circulatory failure after various adverse circulatory conditions, many studies are being performed to clarify the molecular mechanism of estradiol action with regard to tissue circulation. Estradiol improves the macro- and microcirculation of the splanchnic organs by multiple mechanisms. Nonetheless, it remains unclear which mechanism plays the most important role in the treatment of trauma-hemorrhage and sepsis. Additional studies are required to elucidate the precise mechanism of estradiol action and to determine the usefulness of estradiol treatment for severe hemorrhage and sepsis in patients.