Increased Intestinal Marker Absorption Due to Regional Permeability Changes and Decreased Intestinal Transit during Sepsis in the Rat Q . WANG, N. PANTZAR, B. JEPPSSON. B. R. WESTROM & B. W. KARLSSON Dept. of Animal Physiology. Lund University, and Dept. of Surgery, Lund University Hospital. Lund. Sweden

Wang Q, Pantzar N , Jeppsson B, Westrom BR, Karlsson BW. Increased intestinal marker absorption due to regional permeability changes and decreased intestinal transit during sepsis in the rat. Scand J Gastroenterol 1994;29:1001-1008.

Background: The intestinal barrier properties are impaired during inflammation and sepsis, but the mechanisms behind this are unknown and were therefore investigated during experimental sepsis in rats. Methoak: The different-sized intestinal absorption markers 51Cr-labeled ethylenediaminetetraacetic acid (EDTA) and ovalbumin were gavaged to rats made septic by intra-abdominal bacterial implantation and to sham-operated rats. Regional tissue permeability was measured in diffusion chambers, and intestinal transit was evaluated by intestinal accumulation of gavaged "Cr-EDTA. Results: In comparison with the sham-operated rats, septic rats had higher "Cr-EDTA levels in blood and urine and showed a prolonged intestinal transit. Septic rats also had a lower tissue permeability to both markers in the small intestines but higher permeability to ovalbumin in the colon. Rats receiving morphine to decrease intestinal motility showed similar changes, with a decreased intestinal transit and increased marker absorption. Conclusions: The results suggest that the increased intestinal absorption during sepsis was due to regional permeability changes and prolonged intestinal transit.

Key words: Diffusion chamber; "Cr-ethylenediaminetetraaacetic acid; intestine; morphine; ovalbumin; permeability; rat; sepsis; transit

Quan Wang, M . D., Depr. of Animal Physiology, Lund University, Helgonavagen 38. S-22362 Lund. Sweden (fax: +46 46 104539)

The gastrointestinal tract contains a large number of poten- tial pathogenic bacteria, bacterial products, and dietary macromolecules that are prevented from teaching the cir- culation by the presence of an effective intestinal mucosal barrier. In spite of this, the mucosal surface is the major barrier through which bacteria initiate disease processes. Several recent studies. both in humans and animal models, have documented an impairment of the gastrointestinal bar- rier function in association with various pathologic insults, including hemorrhagic shock ( l ) , thermal injury (2,3), trauma (4). intestinal ischemia (5,6), sepsis (7), and endo- toxemia (8-10). In these studies the deterioration of the intestinal mucosal barrier was demonstrated either by deter- mining enteric bacterial translocation across the epithelium into mesenteric lymph nodes, other organs, and blood or by measuring the absorption of various marker substances from the lumen into the circulation.

Increased intestinal absorption of both small and large marker molecules has been demonstrated during experi- mentally induced intestinal inflammation (11,12), and the increase was correlated to the degree of inflammation (11). Even a single intravenous injection of Escherichia coli endo- toxin caused increased intestinal absorption in healthy

humans (13), which may reflect the sensitivity of the intestinal mucosa to an inflammatory challenge. A general inflam- mation, such as sepsis and endotoxemia, also causes impair- ment of the intestinal barrier, as shown by an increased bacterial translocation (7, 10). However, no studies have been done on the intestinal permeability during sepsis and the mechanisms behind the changes of the intestinal barrier function.

The purpose of the present study was to investigate changes in the intestinal barrier properties during experimentally induced sepsis in rats by intra-abdominal implantation of bac- teria. To evaluate the factors involved, the studies were per- formed both in vivo, by gavaging two different-sized marker molecules, chromium-51-labeled ethylenediaminetetraacetic acid (5'Cr-EDTA, Mw 358) and ovalbumin (Mw 45,000), to assess the intestinal absorption capacity, and in vitro, byincu- bating different parts of the intestines in Ussing diffusion chambers to evaluate the tissue permeability in different intestinal regions. Since intra-abdominal sepsis caused an increased accumulation of "Cr-EDTA in the intestines, the possible influence of intestinal transit per se on marker absorption was evaluated in a separate experiment using morphine to reduce gastrointestinal motility.

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1002 Q. Wangeral.

MATERIALS AND METHODS Animals

Male rats of the Sprague-Dawley strain (Mollegaard, Skensved, Denmark), weighing 300-400 g, were kept in polycarbonate cages on chopped wood bedding a i t h a 12-h day/night rhythm at 20 t 2°C and a relative humidity of SO +- 10%. The rats had free access to a rat chow (R3. Astra- Ewos. Sodertalje, Sweden) and tap water.

Indiiction of sepsis The challenge material for the intra-abdominal sepsis

induction was prepared as previously described (14). In brief. equal volumes of cultures of Bacteroides fragilis (2.5 x 10' colony-forming units (CFU)/ml) and E . coli (1.3 x lo7 CFU/ml). isolated from human abscesses, were mixed and added to an equal volume of adjuvant substance (autoclaved rat colonic content and 2 0 4 barium sulfate). This material was stored frozen at -80°C.

The septic challenge material was thawed immediately before use, put in a gelatin capsule (0.75 8). and placed into the right lower abdomen of the rats through a small midline incision during ether anesthesia in accordance with Hansson et al. (14). As a control, sham operation was carried out by a corresponding laparotomy with implantation of empty gelatin capsules. The bacterial challenge. as reported by Hansson et al. (14), resulted in positive blood cultures of E. coli, early leukopenia, decreased blood pressure at 12 h after challenge, and a mortality of approximately 50% ivithin 72 h of challenge. In this study, the development of sepsis was examined at 0, 10, and 24 h after the challenge by counting the leukocytes in 20pl blood from the tail vein. using a Biirker chamber.

Marker absorption in vivo To enable repeated blood sampling, the jugular vein was

catheterized under ether anesthesia 3 days before the chal- lenge of the rats. Twenty-four hours after challenge or sham operation, the rats were fed, by orogastric tube. a marker solution (20 ml/kg body weight) containing 100 mg/ml of ovalbumin (A-7641, Sigma Chemical Co., St. Louis, Mo., USA) and 30pCi/ml of 51Cr-EDTA (NEN. DuPont, Dreieich, Germany) in 0.9% saline, whereafter they were kept in metabolic cages for up to 24,48, or 72 h. After 1 ,2 , 4,8,24,48, and 72 h 1 mi of blood was withdrawn from the jugular vein catheter and replaced with 2ml sterile 0.9% saline. Urine and feces were collected separately from the cages at 4. 8. 24.48, and 72 h . At the end of the experiment the animals were killed, the abdomen was opened. and the intestine, from pylorus to rectum, was divided into six parts by ligation before cutting: the small intestine in four parts of equal length, the cecum, and the colon.

To affect the gastrointestinal motility and thus the intes- tinal transit time, a separate group of rats received sub- cutaneous injections of morphine (10 mg/kg, Kabi Pharmacia, Uppsala, Sweden) every 8 h . After the first

injection (t = 0) the rats were intragastrically fed a marker solution (20 ml/kg body weight) containing ovalbumin (100 mg/ml) and 'lCr-EDTA (22 pCi/ml) and were kept in metabolic cages for up to 24 h. Five rats, receiving marker solution only, were used as controls. Blood, urine, feces, and intestines were sampled as above.

Intestinal transit measurements Intestinal transit in the differently treated rat groups was

estimated by measuring the amount of 51Cr-EDTA remain- ing in different intestinal regions and discharged via the feces collected in the metabolic cages at different time points after marker gavage.

Permeabiliiy experiments Twenty-four hours after septic challenge or sham opera-

tion a midline abdominal incision was performed under ether anesthesia. Two 5-cm segments of the proximal small intestine taken 3 cm distal to the Treitz's ligament, two 5-cm segments of the distal small intestine taken 3 cm proxi- mal to the cecum, and a 6- to 7-cm segment of the colon, starting distal to the cecum and divided into two parts, ascending colon and transverse colon, respectively, were removed and immediately immersed in modified Krebs- Ringer buffer (containing 110.0 mmol/l NaCI, 3.0 mmol/l CaCI2, 5.5 mmol/l KCl, 1.4 mmol/l KH2P02, 29.0 mmol/l NaHC03, 5.7 mmol/l Na-pyruvate, 7.0 mrnol/l Na-fumar- ate, 5.7 mmol/l Na-glutamate, and 13.4 mmol/l glucose, pH 7.4) oxygenated with carbogen (95% O2 and 5% COz) at room temperature. Each segment was cut along the mesenteric border, rinsed in the buffer. and mounted in modified Ussing chambers (15) with an exposed area of 1.78 cm?, as previously described (16). Both the mucosal and serosal reservoirs of the chambers were filled with 5ml buffer, which was continuously oxygenated and circulated by gas lift at 37°C throughout the experiments. When all segments had been mounted, within 30min after the rats had been anesthetized, the buffer was exchanged to fresh buffer in the serosal reservoirs and to the marker solution (t = 0)-that is, buffer containing ovalbumin (25 mg/ml) and '*Cr-EDTA (21 pCi/ml)-in the mucosal reservoirs. After 20,40, 60, 80, 100, and 120 min of incubation, 1-ml samples were taken from the serosal reservoirs for marker analysis and were replaced each time by 1 ml fresh buffer solution.

Analysis Quantitation of ovalbumin in the serosal incubation

samples and in blood serum was performed after each com- pleted experiment by electroimmunoassay, using ovalbumin (A-7641, Sigma) as a standard and a specific rabbit antiserum to ovalbumin raised in our laboratory, as described earlier (16). The radioactivity of 51Cr-EDTA in the serosal samples, whole blood, urine, feces, and intestinal samples (intestinal segments with luminal content) was measured during 300 sec with a well-type gamma counter (LKB, Bromma, Sweden).

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Intestinal Permeability in Septic Rats 1003

30 - a 0 20 - z 2 1 0 -

n o 2

Table I. Leukocyte count/] x (mean +- SE) in vein blood at different time points after sham operation and sepsis induction

* - - Septic - Sham *

* X

* I

I I I I I I

Oh 10h 24 h

Sham Septic

12.5 f 3.8 (n = 18) 12.6 +- 3.2 (n = 18)

11.2 2 1.4 (n = 8) 12.1 f 1.7 (n = 18) 2.9 2 1.0 (n = 8)*** 6.5 2 2.3 (n = 18)***

* * * P < 0.001 indicates significant difference between sham-operated and septic rats

Calculations and statistics The apparent permeability coefficients (Pap,) for the dif-

ferent intestinal regions were calculated from the equation: P,,,(cm.sec-l) = dc/dt.V.(A.Co)-l, where dc/dt is the change of the serosal concentration during 60-120 min'(mol/ l/sec), V is the volume in the reservoirs (cm3), Co is the initial marker concentration in the mucosal reservoirs (mol/ l), and A is the exposed intestinal area in the chamber (cm2). Student's t test was used for statistical evaluation of the data.

RESULTS

After implantation of the bacteria-containing capsule in the peritoneal cavity, the rats showed obvious signs of perito- nitis, with formation of cloudy ascitic fluid and adhesions between the intestines and to the peritoneum in the incision area. Furthermore, the distal part of the small intestine was

enlarged, with a stool-like liquid accumulation in the lumen in some rats, indicating intestinal obstruction. The walls of both the small and the large intestines were swollen, congested, and relaxed. The rats subjected to sham opera- tion and implantation of an empty capsule did not show any marked inflammatory reactions. Moreover, the leukocyte counts were significantly lower in the septic rats at 10 and 24 h after challenge, whereas they were unchanged in the sham-operated animals (Table I). All rats survived 72 h after bacterial challenge.

Absorption experiments in viuo After gavage of the markers the sham-operated rats

showed moderately raised blood levels of 51Cr-EDTA during 4 h, after which the level gradually decreased up to 72 h (Fig. 1A). The septic rats showed significantly increased blood levels after 2 h with an 8-h peak value. The urinary recovery

).

0 30 h U

--m- Morphine - Controls

0 10 20 30 40 50 60 70

Time (h) following gavage

Fig. 1. Appearance of Wr-labeled ethylenediaminetetraacetic acid (EDTA) in blood (percentage of fed dose x mean f SE) from (1A) septic rats (n = 8 at 24 h, n = 5 at 48 h, and n = 2 at 72 h) and sham-operated rats (n = 9 at 24 h, n = 5 at 48 h, and n = 2 at 72 h) and from (1B) morphine-injected (n = 7) and control rats (n = 5 ) at various time points after marker gavage. * P < 0.05, **p < 0.01 represent significant difference between septic and sham-operated rats and tp < 0.05 between morphine- injected and control rats.

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1004 Q. W u n g e t a l .

A Septic

0 Sham

*

T 6

0 - 4 0 - 0 0-24 0-40 0 - 7 2

B

Morphine

E3 Controls

t T

0 - 4 0 - 8 0 - 2 4

Time period (h) following gavage

Fig. 2. Recovery of "Cr-labeled eth) Icnediarninetetraacetic acid (EDTA) (percentage of fed dose. mean 2 SE) in the urine from (2A) septic rats (n = 8 at 24 h. n = 5 at 48 h, and n = 2 at 72 h) and sham- operated rats (n = 9 at 24 h. n = S at 48 h. and n = 2 at 72 h) and from (2B) morphine-injected rats (n = 7) and control rats ( r r = 5 ) at various time periods after gavage. * P < 0.05, **p < 0.01 represent significant difference between septic and sham-operated rats, and tp < 0.05, l'ty .r: 0.01 between morphine-injected and control rats.

of 5iCr-EDTA in the sham-operated rats increased to 2.3% at24 h. whereafter i t remainedconstant (Fig. 2A). The septic rats showed significantly lower urinary recoveries during the first 4 h. which increased thereafter and reached significantly higher levels of 3.9% after 24 h as compared with the sham- operated rats.

The rats receiving morphine showed a rapid appearance of SICr-EDTA in the blood with a 2-h peak value, which then decreased to the level of the control group (Fig. IB). The urinary recovery of SiCr-EDTA in the morphine group increased with time and was significantly higher than in the controls (Fig. 2B).

Intestinal transit measurements In comparison with the sham-operated rats. the septic rats

accumulated more 5'Cr-EDTA in the colon and the cecum and discharged less via the feces during the first 2 1 h after gavage. indicating a decreased intestinal transit. During the next 74 h the septic rats discharged more SiCr-EDTA than the sham-operated ones (Table 11). The rats receiling mor- phine showed changes similar to those in the septic rats and accumulated more in the cecum and the colon and discharged less "Cr-EDTA via feces during 24h than the controls (Table 11).

Pernietibiliry experiments in oitro The time-dependent transmural marker passage was

generally linear in all the intestinal regions for "Cr-EDTA,

whereas the slope of the ovalbumin curve increased slightly, as shown in Fig. 3 for the distal small intestine.

When the calculated permeability coefficients were com- pared for the different intestinal regions in the sham- operated group, the permeability to 'lCr-EDTA was gen- erally higher in the distal intestine (Fig. 4). The ascending colon showed the highest permeability among the intestinal segments but did not differ significantly from that of the transverse colon. For ovalbumin the permeabilities were similar among the regions except for the transverse colon, which was significantly lower. In the septic rats the large- intestinal regions showed a higher permeability than the small-intestinal regions, to both Wr-EDTA and ovalbumin.

When the intestinal permeability in the septic and the sham-operated rats is compared, the permeability coef- ficients in the small intestines for both 'ICr-EDTA and ovalbumin were significantly lower in septic rats. In the ascending colon, however, the septic animals had signifi- cantly higher permeability to ovalbumin and a tendency for higher permeability to "Cr-EDTA (Fig. 4).

DISCUSSION

Several animal models have been used for the study of experimentally induced sepsis (17-19). In the present study we challenged rats by intra-abdominal implantations of capsules with living bacteria and adjuvant substances, since this model mimics the pathophysiology of abdominal abscess

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Intestinal Permeability in Septic Rats 1005

0.01 0 -

0.005 -

Table 11. The amount of "Cr-labeled ethylenediaminetetraacetic acid (percentage of fed dose, mean 2 SE) found in different intestinal regions and the discharge via feces after marker gavage to sham-operated and septic rats or control and morphine-injected rats

Q 1.0-

1

4 a h

a 0.5-

t9

0.0 -I

24 h 48 h 72 h 24 h

Small intestine Sham 0.1 2 0.04 ( n = 5) 0.4 2 0.5 ( n = 3) t Control 0.7 2 0.9 ( n = 5) Septic 1.0 2 0.5 (n = 5) 0.5 2 0.4 ( n = 3) t Morphine 0.6 2 0.4 ( n = 5)

Colon Sham 5.9 2 2.2 ( n = 5) 0.7 2 0.9 (n = 3) 4 Control 2.4 ? 1.4 ( n = 5 ) Septic 10.0 2 2.4 (n = 5) 7.1 2 2.6 ( n = 3): t Morphine 8.5 2 1.5 ( n = 6)t

Cecum Sham 16.4 2 5.5 (n = 5) 2.6 2 2.2 ( n = 3) t Control 5.5 2 2.1 ( n = 5) Septic 33.6 2 5.8 (n = 5)* 18.4 2 7.1 (n = 3)* 4 Morphine 20.8 2 2.6 ( n = 6 ) t t

0-24 h 24-48 h 48-72 h ~ ~~

0-24 h

Feces Sham 39.8 2 5.1 ( n = 10) 14.1 -C 10.7 ( n = 5) 2.0 2 0.1 (n = 2) Control 79.1 2 6.8 ( n = 5 ) Septic 16.5 2 5.2 ( n = lo)** 32.3 2 12.5 ( n = 5)* 4.3 2 2.3 (n = 2) Morphine 30.5 +- 5.1 ( n = 6 ) t t t

* P < 0.05 and * * P < 0.01 indicate significant differences between sham-operated and septic rats. t P < 0.05, tt P < 0.01, and t f f P < 0.001 indicate significant differences between morphine-injected and control rats $ Not done.

formation and sepsis development in man. Furthermore, the host defense mechanisms are able to be fully expressed in this model as compared with models with intravenous or intraperitoneal injections of endotoxin or bacteria. The bacteria used, E. coli and B . fragilis, are the most common and essential bacteria in the pathogenesis of clinical intra- abdominal abscess formation and sepsis. In this study a well-developed sepsis was achieved, as evident from the leukopenia. However, there were no deaths during the 72-h experimental period, in contrast to the original report of the model (14). An explanation for this might be a decreased bacterial virulence with storage time or a batch different from the original one.

1-51

(A) 5 1Cr-EDTA * * * - - septic - Sham

* u. ii/ /

Several investigations have shown bacterial translocation or increased intestinal permeability after sepsis and endo- toxicosis (10, 20-22). The suggested causes of the impaired intestinal barrier function have been a decreased mesenteric blood flow, which may result in mucosal hypoxia (23), and luminal bacterial overgrowth with subsequent effects of their toxic products, which may either directly alter the structure and function of the intestinal epithelium (9) or activate cells, such as neutrophils, able to cause damage by the release of oxygen radicals, proteolytic enzymes, and inflammatory mediators (24). However, impaired intestinal barrier proper- ties have also been found in the intestines without direct evidence of mucosal damage after histologic examination

(B) Ovalbumin * 0.015 1 *

O.OO0 1 0 20 40 60 00 100 120 0 20 40 60 00 100 120

Time (min) of incubation

Fig. 3. Time-dependent mucosal to serosal passage in percentage (mean 2 SE) of 51Cr-labeled ethylene- diaminetetraacetic acid (EDTA) (3A) and ovalbumin (3B) through distal small-intestinal tissue from septic (n = 13) and sham-operated rats (n = 14) mounted in diffusion chambers. **P < 0.01 and ***p < 0.001 represent significant difference between the septic and sham-operated rats.

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1006 Q. Wang et al.

a

E *z a 5

e

z

(D > 0 k

h

'4

X

2 0 W

a 4 a

0 septic 0 Sham

811 Septic Li3 Sham

*'O 1 * T

1.5

1 .o

0.5

0.0 J e j u n u m Ileum Ascending Transverse

colon colon (n=16) (n=16) (n=7) (n=7)

Fig. 4. Apparent permeability coctfcients (cm sec-' X mean & SE) of "0-labeled ethylene- diaminetetraacetic acid (EDTA) and ovalbumin in different parts of the intestine from septic and sham- operated rats, calculated from the passage curves between 60 and 120min in diffusion chambers. " P < 0.05 and * * p < 0.01 represent hignificant difference.

(25,26), implying that the relationship between the seventy of mucosal barrier damage and intestinal permeability needs to be further investigated.

In accordance with previous human studies and studies on animal models (11. 13.23). we found an increased absorp- tion into blood and an increased urinary recovery of 51Cr- EDTA in septic rats as compared with the sham-operated rats. Unfortunately. the blood levels of the macromolecular marker ovalbumin were too low in vivo to enable adequate quantitation with electroimrnunoassay, but Ramage et al. (27) reported a correlation between intestinal absorption of the low-molecular marker 51Cr-EDTA and ovalbumin during intestinal inflammation.

The most important result of the present study was the elucidation of the mechanisms behind the impaired intestinal barrier properties during septic conditions. In addition to the increased intestinal marker absorption, the septic rats showed luminal accumulation of "Cr-EDTA together with a decreased elimination via feces. indicating that intestinal transit had been prolonged. These results raised the question of whether a prolonged intestinal transit time per se could influence marker absorption across the intestinal barrier. This question was further studied in rats receiving morphine, since studies have shown that morphine increased the intes- tinal transit time in a dose-dependent manner, although the mechanisms of this prolonged transit via the reduction in

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Intestinal Permeability in Septic Rats 1007

contractile frequency or increase of non-propulsive con- traction in the small intestine are contradictory (28,29).

Our results showed that rats receiving morphine accumu- lated more 51Cr-EDTA in the intestines and had a decreased elimination via feces than the controls, thus indicating a prolonged intestinal transit. In parallel to this, the morphine- injected rats also showed an increased? qrinary recovery of 'lCr-EDTA, demonstrating the cone intestinal transit and total marker absorption. This finding is supported by another study in which an increased intestinal transit, obtained after ingestion of a poorly absorbed lactulose solution, reduced the intestinal absorption of marker molecules (30). Moreover, recent studies (31,32) showed that an increased intestinal transit time after mor- phine administration promoted bacterial translocation across the intestines. However, morphine administration may also have other effects on the gastrointestinal tract affecting the total absorption of marker molecules. For example, vasodilation, induced by morphine via peripheral histamine release (33,34). could influence mesenteric blood flow, and morphine may also act directly on mucosal epithelial cell secretion (35) and/or absorption. These latter possibilities need to be further investigated.

Nevertheless, the septic rats in the present study showed changes similar to those of the morphine-injected rats, sug- gesting that the increased absorption of %3-EDTA after septic challenge was a result not only of the changed mucosal barrier function per se but also of the prolonged intestinal transit. A prolonged intestinal transit time may also affect luminal bacterial overgrowth, which could aggravate the barrier damage. Therefore, intestinal transit is an important factor for the total absorption of markers over the gut, probably by influencing the contact time between the marker molecules and the intestinal mucosa. Possible changes of the intestinal transit time in vivo during various pathologic conditions is seldom taken into consideration in intestinal absorption measurements, although they may play a role for the interpretation of the results in such studies.

To obtain information about the regional intestinal barrier properties during sepsis, intestinal segments were incubated in diffusion chambers with the same markers as used in vivo. The results obtained showed evident regional differences with a generally increasing permeability in the proximal to distal direction of the gut. The septic rats showed a decreased permeability to both markers in the small intestines, whereas the ascending colon instead had a significantly increased permeability to ovalbumin and a tendency of increase for 51Cr-EDTA. These changes in permeability in the different intestinal regions were consistent with the in vivo results. The septic rats showed delayed blood peak values and lower urinary recoveries after 4 h than the sham-operated rats, consistent with the decreased small-intestinal permeability, but higher urinary recoveries at 24 h, consistent with the increased colon permeability. These results thus indicate that the experimentally induced sepsis results in regional

#:-:

permeability changes affecting the intestinal barrier func- tion.

The reason for the observed reduced permeability in the small intestines of the septic rats is not clear. Some septic rats showed obvious signs of intestinal obstruction, mainly in the small intestines; however, it has been shown that intestinal obstruction rather causes an increased bacterial translocation (36). The decreased permeability of the small intestines in septic rats could alternatively be explained by edema of the intestinal wall, which would increase the diffusion distance for the markers and thereby decrease the permeability. Furthermore, an increase in local host defense in the small intestines may also be of importance. Increased elimination of the markers by infiltrating leukocytes in the inflamed small intestines (12) may result in an apparent decreased permeability.

Hansson (37) showed a decrease in blood flow, to 50% of the control, in the large intestine during sepsis but no change in the small intestines, which suggests that ischemia in the large intestine could contribute to the impaired barrier function in this region during experimentally induced sepsis. This is supported by a general sensitivity of the bowel mucosa to ischemia (6,24,38) and the importance of mesenteric hypoperfusion as an etiologic factor contributing to derange- ment of the barrier function in experimental endotoxicosis (23). Thus, there are alternative explanations of the different changes in permeability between the small and large intes- tines during experimentally induced sepsis, which need to be further studied. Anyhow, the increased permeability in the large intestine during sepsis may have clinical signifi- cance, since this region contains large amounts of bacteria and their toxic products, which could reach the circulation and aggravate the pathologic condition.

The results of the present study have shown an increased permeation of marker molecules across the intestinal wall during experimentally induced sepsis, due to both regional permeability changes with increases in the large intestine and prolonged intestinal transit. These findings are of potential interest from a therapeutic point of view. They point to the intestinal transit time as an important factor for the total absorption in the gut. The study also gives some support to undertake measures aimed at reducing or altering the colonic bacterial flora to diminish any harmful effects of bacterial translocation in abdominal sepsis.

ACKNOWLEDGEMENTS

The authors thank Inger Mattsson for expert technical assist- ance. The study was supported by grants from the Swedish Natural Sciences Research Council, the Royal Physio- graphical Society of Sweden, the Craaford Foundation, the Ekhaga Foundation, and a World Health Organisation fel- lowship to Q. Wang.

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1008 Q. Wang etal.

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