Endotoxin (LPS) increases mesenteric vascular resistance (MVR) and bacterial translocation (BT)

Bacterial translocation, intestinal ultrastructure and cell membrane permeability early after major liver resection in the rat

The process and route of bacterial translocation from the gut after major liver resection remain unclear. In the present study enteric bacterial translocation, enterocyte ultrastructure in the ileum and colon, the process and route of bacterial invasion and the permeability of the cell membrane system and blood-tissue barrier were evaluated in rats receiving sham operation, and 70 or 90 per cent hepatectomy. The incidence of bacterial translocation to mesenteric lymph nodes was 80-100 per cent in rats 6 h after 70 per cent and 2-4 h after 90 per cent hepatectomy, and 80-100 per cent to the systemic circulation 2-4 h after 90 per cent hepatectomy but only 20 per cent to the portal vein. An increase in bacterial adherence to the intestinal surface, damage to the permeability of the cell membrane system and blood-tissue barrier, and pathological alterations in the ileum and colon developed, correlating with the extent of liver removed and the time that had passed after hepatectomy. Most translocating bacteria appeared in morphologically intact enterocytes with increased membrane permeability, in antigen-presenting cells and in submucosal lymphatics, but some bacteria were also seen within damaged enterocytes 4h after 90 per cent hepatectomy. These results indicate that altered permeability of the cell membrane system may be one of the earliest characteristics of challenged enterocytes, and that enteric bacteria translocate through both morphologically normal and abnormal enterocytes. Translocation occurred mainly into the lymphatics, bacteria either being 'carried' by antigen-presenting cells or entering by active invasion.

Peritonitis impairs intestinal absorption of proline and leucine in the rat

Systemic sepsis is associated with reduced mesenteric blood flow and impairment of metabolic and barrier functions of the small intestine. A study was performed in the rat to investigate the effect of sepsis induced by caecal ligation and double puncture on intestinal absorption of leucine and proline in vivo. Absorption was studied 24 h after caecal ligation and puncture by measuring intestinal disappearance and circulatory appearance of intraluminal 3H-labelled amino acid over a 60-min study period. Peritonitis resulted in a significant increase relative to controls in the mean (s.e.m.) percentage of leucine (67.2(3.6) versus 18.0(3.5), P < 0.001) and proline (64.7(6.0) versus 15.1(3.7), P < 0.001) remaining within the small intestine. There were significant decreases in portal venous and femoral arterial concentrations of leucine and proline in animals with sepsis. Intestinal amino acid absorption is impaired in this model.

The role of the imino transporter protein in sepsis-impaired intestinal proline absorption

Recently, sepsis has been shown to impair intestinal amino acid absorption in addition to gut metabolic and barrier functions. We investigated intestinal proline absorption in a rabbit model of sepsis. Twelve hours after intraperitoneal injection of lipopolysaccharide, proline uptake by everted jejunal sacs prepared from septic animals (480.4 +/- 67.4 nmol per sac per hour) was significantly reduced compared with controls (846.8 +/- 73.5 nmol per sac per hour) (p < .001 by t test). We next investigated whether reduced expression of transporter proteins contributed to the impaired intestinal proline uptake during sepsis. The proline (imino) carrier of rabbit jejunum is covalently bound by fluorescein isothiocyanate (FITC) and/or phenylisothiocyanate with irreversible inhibition of proline uptake. This binding and inhibition is prevented by sodium chloride and L-proline. Single-cell suspensions of rabbit enterocytes were prepared 12 hours after intraperitoneal injection of lipopolysaccharide/saline or saline alone. Enterocytes were incubated for 30 minutes in tris(hydroxymethyl)aminomethane/ethylenediaminetetraacetate (Tris/EDTA) buffer; buffer with 1 mM phenylisothiocyanate; or buffer with 10 mM proline, 100 mM sodium chloride, and 1 mM phenylisothiocyanate. After incubation with 10 microM FITC in Tris/EDTA buffer for 15 minutes, the percent positivity and fluorescent intensity of FITC binding to enterocytes were determined by using flow cytometry. Sepsis significantly reduced the percentage of enterocytes binding FITC and the fluorescent intensity of FITC binding of proline/sodium chloride-pretreated or untreated cells. This suggests that sepsis depresses the expression of imino transporters by rabbit enterocytes, which may explain the reduced intestinal proline absorption.

Intestinal amino acid absorption during sepsis

Sepsis has been shown to cause a decrease in mesenteric blood flow in association with ultrastructural changes in the small intestine and impaired immune, barrier, and metabolic functions of the gut. These impairments in the structure and function of the gastrointestinal tract may have a detrimental effect on the morbidity and mortality of sepsis. Two recent studies have shown that the ability of the small intestine to absorb amino acids is also impaired during sepsis, but the systemic and cellular mechanisms of this impairment are not known. Release of cytokines induced by systemic bacteria or endotoxin may lead to a reduction in the synthesis of transporter proteins by the enterocyte at a time when there is reduced availability of both luminal (because of anorexia) and circulating (because of reduced mesenteric blood flow) substrates. Future research needs to investigate the systemic and local mediation of the sepsis-induced reduction in intestinal amino acid absorption and the possibility of correcting the defect by the administration of enteral nutrients, hormones, or drugs.

Sequential changes in the splanchnic circulation during continuous endotoxin infusion in sedated sheep: evidence for a selective increase of hepatic artery blood flow and loss of the hepatic arterial buffer response

On-line recording of the sequential changes in systemic, pulmonary, mesenteric, hepatic and renal circulations during onset of endotoxaemia and at 24 h of established hyperdynamic sepsis were evaluated in seven chronically instrumented and sedated sheep receiving a continuous intravenous infusion of Escherichia coli endotoxin (20 ng min-1 kg-1). A transient and significant (P < 0.05) pulmonary arterial vaso-constriction was noted after 13 +/- 4 min, and was followed immediately by a simultaneous significant decrease of coeliac trunk, superior mesenteric artery, and portal vein blood flow to below 50% of baseline values. The superior mesenteric artery and portal vein blood flows partially recovered pre-endotoxin levels to 69 and 75% of baseline, respectively, after 70 min of endotoxin infusion. In contrast, the coeliac trunk blood flow remained reduced for a more prolonged period of time, but then completely recovered baseline values at 100 min. The response of the hepatic artery was biphasic, and consisted of a transient (5-10 min) vasoconstriction at 40 min followed by transitory increase of hepatic artery blood flow reaching a maximum of 921% of baseline values at 102 min. Contrasting with the early changes observed in mesenteric vascular resistances mostly unrelated to systemic haemodynamics, the response of the renal vasculature appeared to be more dependent on changes of renal perfusion pressure. A follow-up at 24 h revealed that the continuous intravenous infusion of endotoxin reproduced some of the most characteristic features of human sepsis with increased cardiac output and decreased vascular resistances of all vascular beds. We conclude that hepatic artery blood flow is selectively and considerably increased in early endotoxaemia in sheep independently of changes in portal vein blood flow, suggesting a disregulation of the physiologic hepatic arterial buffer response, most probably secondary to an increased liver oxygen demand required for phagocytosis, transport, and digestion of the the sudden overload of bacterial endotoxins.

Sepsis impairs gut amino acid absorption

Sepsis has been shown to adversely affect the barrier and metabolic functions of the small intestine as well as to reduce mesenteric blood flow and cause histologic damage. However, the effect of sepsis on gut absorptive function has been largely ignored. In this study, intestinal absorption of arginine and an amino acid analogue, aminoisobutyric acid, was studied using in vivo and in vitro techniques in an experimental model of sepsis. In vivo studies showed a significant impairment in the absorption of both amino acids from the intestinal lumen 24 and 72 hours after cecal ligation and puncture. Uptake of these amino acids by everted gut sacs prepared from septic animals was also significantly reduced. This reduction in absorptive capacity of the gut may limit the ability of enteral feeding alone to supply nutritional requirements during sepsis and may also contribute to the associated morbidity and mortality.

The effect of surgical trauma on the bacterial translocation from the gut

Bacterial translocation is the passage of viable bacteria from the lumen of the gastrointestinal tract through the intestinal mucosa to other sites. It is believed that bacterial translocation may lead to infection and septicemia. The purpose of this study was to determine what factors in experimental surgical trauma lead to bacterial translocation. Two-month-old Wistar albino rats were divided into five groups: (A) control; (B) anesthesia (ether inhalation); (C) anesthesia and surgery (median laparotomy and transient compression of the intestines); (D) fasting only; and (E) anesthesia, surgery, and fasting. After 48 hours, ileum, mesenteric lymph nodes, and blood were cultured for aerobic and anaerobic organisms. In each group the number of animals with bacteria overgrowth was calculated. The incidence of bacterial translocation to mesenteric lymph nodes and blood in groups B and D were similar to the controls (P greater than .01). There was a significant increase in the number of animals with bacterial translocation in groups C and E (P less than .001). The majority of translocating bacteria were E coli.

Decreased mesenteric blood flow in experimental multiple organ failure

Disorders of mucosal blood flow may contribute to gut barrier dysfunction in multiple organ failure (MOF). We evaluated alterations of mesenteric microcirculation in a rat model of MOF. Male Wistar rats received 1 mg/g body weight of zymosan A in 4 ml of mineral oil by intraperitoneal injection and were studied on Days 1, 3, and 5 following injection. A control group received no zymosan. The experimental group also received a fluid resuscitation regimen of 0.9 N saline subcutaneously equal to 0.1 ml/g body weight on the day of zymosan injection and 0.05 ml/g body weight daily thereafter. Day 1 animals tended toward a statistically significantly lower mean arterial pressure versus controls (86.6 +/- 8 mm Hg versus 106 +/- 5 mm Hg, F = 0.09 by ANOVA). Significant arteriolar vasoconstriction occurred on Days 1 and 3 versus control (70 +/- 4 microns and 57 +/- 8 microns versus 96 +/- 3 microns, F = 0.0002). Laser doppler velocity, indicating red blood cell velocity, expressed as a percentage of control paralleled this vasoconstriction (70 +/- 9 and 72 +/- 7%, respectively). We conclude that mesenteric arteriolar vasoconstriction occurs accompanied by decreased red blood velocity. We believe that this is indicative of decreased mesenteric perfusion in this zymosan model of MOF and that survival to Day 5 is associated with a reversal of these microcirculatory changes.