Hepatic glucose metabolism during intraduodenal glucose infusion: impact of infection

Owen P. McGuinness, Joseph Ejiofor, D. Brooks Lacy, and Nancy Schrom

Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232


    ABSTRACT
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

We previously reported that infection decreases hepatic glucose uptake when glucose is given as a constant peripheral glucose infusion (8 mg · kg-1 · min-1). This impairment persisted despite greater hyperinsulinemia in the infected group. In a normal setting, hepatic glucose uptake can be further enhanced if glucose is given gastrointestinally. Thus the aim of this study was to determine whether hepatic glucose uptake is impaired during an infection when glucose is given gastrointestinally. Thirty-six hours before study, a sham (SH, n = 7) or Escherichia coli-containing (2 × 109 organisms/kg; INF; n = 7) fibrin clot was placed in the peritoneal cavity of chronically catheterized dogs. After the 36 h, a glucose bolus (150 mg/kg) followed by a continuous infusion (8 mg · kg-1 · min-1) of glucose was given intraduodenally to conscious dogs for 240 min. Tracer ([3-3H]glucose and [U-14C]glucose) and arterial-venous difference techniques were used to assess hepatic and intestinal glucose metabolism. Infection increased hepatic blood flow (35 ± 5 vs. 47 ± 3 ml · kg-1 · min-1; SH vs. INF) and basal glucose rate of appearance (2.1 ± 0.2 vs. 3.3 ± 0.1 mg · kg-1 · min-1). Arterial insulin concentrations increased similarly in SH and INF during the last hour of glucose infusion (38 ± 8 vs. 46 ± 20 µU/ml), and arterial glucagon concentrations fell (62 ± 14 to 30 ± 3 vs. 624 ± 191 to 208 ± 97 pg/ml). Net intestinal glucose absorption was decreased in INF, attenuating the increase in blood glucose caused by the glucose load. Despite this, net hepatic glucose uptake (1.6 ± 0.8 vs. 2.4 ± 0.9 mg · kg-1 · min-1; SH vs. INF) and consequently tracer-determined glycogen synthesis (1.3 ± 0.3 vs. 1.0 ± 0.3 mg · kg-1 · min-1) were similar between groups. In summary, infection impairs net glucose absorption, but not net hepatic glucose uptake or glycogen deposition, when glucose is given intraduodenally.

alanine; lactate; inflammation; glycogen


    INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

INFECTION LEADS TO MARKED alterations in whole body glucose production and utilization. The increase in glucose production is predominantly caused by acceleration in gluconeogenesis, which is driven by elevated counterregulatory hormones and increased gluconeogenic precursor supply (15). In addition to the increase in glucose flux, whole body energy expenditure is increased (10). To meet the increased caloric requirements, many of these individuals require nutritional support.

Glucose intolerance and insulin resistance are often present during stressful conditions, especially when exogenous glucose must be administered. The hyperglycemia commonly seen in individuals with infections (11, 25) is a result of alterations in both liver and muscle glucose metabolism. Under feeding conditions, the liver is an important site for glucose disposal. We observed during a continuous intravenous infusion of glucose that the liver removed ~30% of the infused glucose in normal dogs (17). The ability of the liver to dispose of the glucose was decreased by infection (17). Net hepatic glucose uptake was decreased because of an attenuated suppression of hepatic glucose production, as well as augmentation of unidirectional hepatic glucose uptake (17). Thus, for the same glucose infusion rate, infection forced insulin-resistant peripheral tissues to dispose of the additional glucose. Failure of the liver to take up glucose predisposes an individual to develop hyperglycemia. In individuals with diabetes (19) who are prone to infections, the severe hyperglycemia can limit the calories that are given.

The impaired liver glucose uptake seen in stressed patients may be improved if glucose is given via the oral route. Previous studies indicate that the route of glucose delivery is important in determining the magnitude of net hepatic glucose uptake. Indeed, oral administration of glucose enhances net hepatic glucose uptake to a greater extent than when the glucose is administered via a peripheral vein (23). If the oral delivery of glucose can overcome the infection-induced impairment in liver glucose uptake, glucose carbon can be diverted to the liver and away from the insulin-resistant tissues in the stressed individual. This, in turn, could limit the hyperglycemia and the insulin required to maintain normoglycemia. Thus the aim of this study was to determine whether the infection-induced impairment in net hepatic glucose uptake seen after peripheral infusion of glucose could be overcome by intraduodenal administration of glucose.


    METHODS
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Animal Preparation

Experiments were carried out on 14 conscious female mongrel dogs (21 ± 1 kg). Before being studied, they received a diet consisting of Kal-Kan meat (Vernon, CA) and Purina dog chow (St. Louis, MO) once daily. The composition of the diet was 52% carbohydrate, 31% protein, 11% fat, and 6% fiber, based on dry weight. The dogs were housed in a facility that met the guidelines of the Association for Assessment and Accreditation of Laboratory Animal Care International. The Vanderbilt University Animal Care and Use Committee approved the experimental protocols.

Surgical Preparation

Fourteen to seventeen days before study, a laparotomy was performed under general anesthesia (isoflurane). Sampling catheters (0.04 inch ID) were inserted into the portal vein and the left common hepatic vein for blood sampling. An infusion catheter was placed into the duodenum. Additional catheters (0.04 inch ID) for blood sampling were inserted into the femoral artery after an incision in the left inguinal area. The catheters were then filled with saline containing heparin (200 U/ml). Doppler flow probes were placed around the portal vein and the hepatic artery after the gastroduodenal vein had been ligated. The portal and hepatic vein sampling catheters, the intraduodenal infusion catheter, and the Doppler flow probe leads were exteriorized and placed in a subcutaneous pocket in the abdominal area. The femoral artery sampling catheter was placed under the skin in the inguinal region (18).

Two weeks after catheter implantation, all animals had 1) a good appetite (consuming the entire daily ration), 2) a normal stool, 3) a hematocrit >35%, and 4) a leukocyte count <18,000 mm-3.

Induction of Infection

The model used is nonlethal (15) and is similar to the model of Fink et al. (7). Approximately two weeks after catheter implantation, a fibrin clot was prepared from a 1% bovine fibrinogen solution (10 ml/kg; Sigma Chemical, St. Louis, MO), which was then filtered through a sterile 0.2-µm filter. On the day before clot implantation, 1 liter of trypticase soy broth (Becton Dickinson, Cockeysville, MD) was inoculated with bacteria and incubated overnight at 37°C. The next day, the bacteria were pelleted by centrifugation, washed with sterile saline, and reconstituted in 20 ml of sterile saline. The dose of bacteria (Escherichia coli; American Type Tissue Culture #25922) was 2 × 109 organisms/kg. The concentration of bacteria was determined by serial dilution of the bacteria followed by plating. The bacteria were mixed with the fibrinogen, and thrombin (1,000 U) was added to initiate clot formation. The sham group received a fibrin clot that did not contain bacteria. After an overnight fast (18 h), dogs were placed under general anesthesia. An abdominal midline laparotomy incision was made at a point below that made 2 wk earlier, and the fibrin clot was placed into the peritoneal cavity. Dogs received 500 ml of saline immediately after clot implantation. An additional 1,000 ml were given the next morning. The dogs were fasted after implantation of the clot.

Experimental Protocol

Thirty-six hours after implantation of the clot, the sampling and infusion catheters and the free ends of the transonic flow probes were removed from the subcutaneous pockets under local anesthesia (2% lidocaine). The dog was then placed in a Pavlov harness, and angiocaths were inserted percutaneously into the right and left cephalic veins. At -120 min, a primed continuous infusion of [3-3H]glucose (50 µCi; 0.4 µCi/min) and a continuous infusion of indocyanine green dye (0.1 mg · m2 · min-1) were begun into the right cephalic vein and were continued for the duration of the study. Hepatic artery and portal vein blood flow were assessed by use of Transonic flow probes (Transonic Systems, Ithaca, NY). After an 80-min tracer and dye equilibration period, blood samples were taken at -40, -20, and 0 min from the three sampling catheters (femoral artery, portal vein, and hepatic vein). After the control period, a glucose bolus (150 mg/kg), followed by a continuous (8 mg · kg-1 · min-1) infusion of glucose containing [U-14C]glucose (~2 µCi/g), was given into the duodenum for 240 min. Blood samples were taken every 30 min from the three sampling catheters for the duration of the study. At the end of the study, each dog was killed with an overdose of pentobarbital sodium. Biopsies of liver were rapidly taken from each of the seven lobes for the determination of glycogen content and tracer incorporation into glycogen. The liver was then removed and weighed.

Processing of Blood Samples

Blood samples were drawn into heparinized syringes and transferred to chilled tubes containing potassium EDTA (15 mg). The collection and immediate processing of blood samples has been previously described (15). 14CO2 in blood was assessed in triplicate by acidifying blood with HCl and trapping the 14CO2 on filter paper saturated with hyamine hydroxide (8). Blood glucose, lactate, glycerol, and alanine were analyzed according to the method of Lloyd et al. (13) on a Monarch 2000 centrifugal analyzer (Lexington, MA). Plasma glucose was assayed immediately with a Beckman Glucose Analyzer II (Beckman Instruments, Fullerton, CA). Immunoreactive plasma insulin (27) was assayed by means of a double antibody technique [Pharmacia Diagnostics, Piscataway, NJ; intra-assay coefficient of variation (CV) of 11%]. Plasma (1 ml) treated with 500 kallikrein inhibitor units of Trasylol (Miles, Kankakee, IL) was assayed for immunoreactive glucagon (1) with a similar procedure as for insulin (intra-assay CV of 8%). Plasma cortisol (5) was assayed with a Clinical Assays Gamma Coat RIA kit (intra-assay CV of 6%). Plasma collected from blood samples that had been immediately treated with EGTA and glutathione were assayed for epinephrine and norepinephrine with HPLC [CV of 14%;(14)]. Hepatic glycogen was assayed according to the method of Chan and Exton (3).

Calculations

Net hepatic glucose uptake was calculated by use of the formula [(Fa × A) + (Fp × P) - H] × HBF, where A, P, and H are the blood glucose concentrations in the femoral artery, portal vein, and hepatic vein, respectively, and Fa and Fp represent the fractional contributions of the hepatic artery and the portal vein, respectively, to total hepatic blood flow (HBF). Hepatic glucose load was calculated by use of the formula [(Fa × A) + (Fp × P)] × HBF. Net hepatic glucose fractional extraction was calculated as the ratio of net hepatic glucose uptake and hepatic glucose load. Plasma glucose concentrations were converted to whole blood concentrations with a correction factor for each vessel and for each animal (21). That equation was used to calculate net hepatic lactate, alanine, and glycerol uptake as well.

The rates of total glucose appearance (Ra) and clearance rates and [14C]glucose appearance rate were calculated according to the method of Wall et al. (26a), as simplified by Debodo et al. (4a). Endogenous glucose production was calculated as the difference between Ra and meal-derived glucose appearance rate. The meal-derived glucose appearance rate was calculated as the total [14C]glucose appearance rate (dpm · kg-1 · min-1) divided by the meal [14C]glucose specific activity (dpm/mg), where dpm is disintegrations per minute. Hepatic glucose oxidation was calculated during the last hour of the experimental period as the ratio of the net hepatic 14CO2 output and the average inflowing [14C]glucose specific activity. Tracer-determined glycogen synthesis (mg · kg-1 · min-1) was calculated as the ratio of hepatic [14C]glycogen content [(14C dpm/g liver × liver wt)/(body wt × 240 min)] and the average inflowing [14C]glucose specific activity (dpm/mg).

Intestinal substrate output was calculated as (P - A) × Fp × HBF. Because the intestine can be both a consumer and a producer of glucose during intraduodenal glucose delivery, we calculated the unidirectional absorption of glucose (Gut Ra) as the sum of meal-derived gut glucose output and unidirectional gut glucose uptake. Because the absorbed glucose contained [14C]glucose, the meal-derived gut glucose output was calculated as the ratio of net gut [14C]glucose output and meal glucose specific activity. Unidirectional gut glucose uptake was calculated as the ratio of net gut [3H]glucose uptake and arterial glucose specific activity. If the site of glucose uptake were common with or distal to the site of glucose absorption, the use of inflowing glucose specific activity would underestimate gut glucose output and, consequently, absorption. In the case of glucose, the fall in [3H]glucose specific activity in the portal vein was small, and therefore, the potential error is small.

Statistics

Hepatic blood flow and substrate flux are expressed as kilograms of body weight. Data are expressed as means ± SE. Data presented for the experimental period are the average of the last 60 min of the experimental period unless otherwise indicated. Statistical comparisons were made by means of analysis of variance (Systat for Windows; Systat, Evanston, IL). A univariate post hoc F-test was used when a significant F ratio was found. Statistical significance was accepted at P < 0.05.


    RESULTS
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Basal Period

Hemodynamic parameters. Infection increased body temperature, heart rate, and hepatic arterial flow; mean arterial blood pressure and portal vein blood flow remained unaltered (Table 1; Fig. 1). Consequently, total hepatic blood flow increased by ~30% (34.9 ± 4.6 vs. 47.2 ± 3.2 ml · kg-1 · min-1, sham vs. infected, respectively; P < 0.05).

                              
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Table 1.   Impact of infection on basal hemodynamic and metabolic parameters in chronically catheterized conscious dogs



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Fig. 1.   Hepatic arterial, portal vein, and total hepatic blood flow in infected (n = 7) and sham (n = 7) clot dogs receiving a primed continuous infusion of glucose into the duodenum. Data are expressed as means ± SE (per kg body wt, where applicable).

Metabolic parameters. Arterial plasma glucose concentrations (Table 1) were similar in the two groups, whereas whole body glucose appearance (2.1 ± 0.2 vs. 3.3 ± 0.1 mg · kg-1 · min-1) and clearance (2.2 ± 0.2 vs. 3.7 ± 0.2 ml · kg-1 · min-1) were characteristically increased (P < 0.05) by infection. The liver was a net consumer of lactate (9.5 ± 2.1 vs. 15 ± 2.5 µmol · kg-1 · min-1, sham vs. infected; P < 0.05) and alanine (2.7 ± 0.4 vs. 3.6 ± 0.7 µmol · kg-1 · min-1) in the basal period. Arterial insulin concentrations were similar (8.0 ± 1.6 vs. 8.2 ± 1.5 µU/ml; sham vs. infected), whereas arterial plasma glucagon concentrations were markedly elevated (53 ± 8 vs. 680 ± 207 pg/ml; P < 0.05; Fig. 2). Arterial cortisol concentrations were also elevated (1.3 ± 0.2 vs. 4.2 ± 0.7 µg/dl; P < 0.05). Arterial epinephrine concentrations were not altered (108 ± 30 vs. 124 ± 50 pg/ml), whereas arterial plasma norepinephrine concentrations were elevated (268 ± 69 vs. 430 ± 89 pg/ml; P < 0.05).


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Fig. 2.   Arterial plasma insulin and glucagon concentrations in infected (n = 7) and sham (n = 7) clot dogs receiving a primed continuous infusion of glucose into the duodenum. Data are expressed as means ± SE (per kg body wt, where applicable).

Response to Intraduodenal Glucose Infusion

Hepatic blood flow and pancreatic hormones. Hepatic arterial and portal vein blood flows were not altered by intraduodenal glucose infusion (Fig. 1). Arterial plasma insulin concentration increased to similar concentrations in both groups; however, the initial rise was faster in the sham group (Fig. 2). Arterial plasma glucagon concentrations decreased in both groups (53 ± 8 to 30 ± 2 vs. 680 ± 207 to 269 ± 128 pg/ml; P < 0.05; basal period to average of last 60 min of the experimental period); however, the absolute decrease in glucagon was greater in the infected group (Fig. 2).

Intestinal substrate kinetics. Although arterial glucose concentrations increased rapidly in both groups, the initial rise in glucose was faster in the sham group (Fig. 3). This was paralleled by a faster rise in both net intestinal glucose output and unidirectional intestinal glucose output (P < 0.05). During the last hour of the study, we could account for 75 and 55% of the glucose infused in the sham and infected groups, respectively. The absorption of glucose created a negative arterial-portal blood glucose gradient of 20 ± 4 vs. 13 ± 3 mg/dl (sham vs. infected) during the last hour of the study. Thus the portal vein blood glucose concentrations tended to be lower in the infected group (150 ± 10 vs. 135 ± 7 mg/dl; Fig. 3) during the last hour of the study.


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Fig. 3.   Arterial and portal blood glucose concentrations, net intestine glucose output, and unidirectional intestinal glucose output in infected (n = 7) and sham (n = 7) clot dogs receiving a primed continuous infusion of glucose into the duodenum. Data are expressed as means ± SE (per kg body wt, where applicable).

The production of lactate by the intestine in the basal period was not increased by intraduodenal glucose infusion in either group (Table 2). The net production of alanine by the intestine in the basal period increased (P < 0.05) after intraduodenal glucose infusion in both groups. Net intestinal glycerol uptake was unaltered by intraduodenal glucose infusion.

                              
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Table 2.   Intestinal lactate, alanine, and glycerol output in infected and sham clot dogs receiving a primed continuous infusion of glucose into the duodenum

Hepatic substrate kinetics. The liver switched from being a net producer (net hepatic glucose utpake is negative) to a net consumer of glucose (net hepatic glucose uptake is positive) in both groups (Fig. 4) during glucose infusion. Net hepatic glucose fractional extraction and hepatic glucose load were similar in both groups. Tracer-determined endogenous glucose production decreased in both groups (1.0 ± 0.2 vs. 1.2 ± 0.2 mg · kg-1 · min-1, sham vs. infected).


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Fig. 4.   Hepatic glucose load, net hepatic glucose output, and net hepatic glucose fractional extraction in infected (n = 7) and sham (n = 7) clot dogs receiving a primed continuous infusion of glucose into the duodenum. Data are expressed as means ± SE (per kg body wt, where applicable).

After glucose infusion, the uptake of lactate by the liver decreased (0.5 ± 1.7 vs. 5.6 ± 3.1 µmol · kg-1 · min-1; Fig. 5). By the last hour of the study, the liver was no longer a significant consumer of lactate in the sham group, whereas the liver of the infected group remained a significant consumer of lactate (P < 0.05). The fall in net hepatic lactate uptake occurred despite a concomitant rise in arterial blood lactate concentrations. Arterial blood alanine concentrations (Fig. 6) increased after glucose infusion. Net hepatic alanine uptake was not altered in either group because of a reciprocal fall in net hepatic alanine fractional extraction. Arterial blood glycerol concentrations decreased (P < 0.05) in both groups (90 ± 8 to 54 ± 12 vs. 74 ± 5 to 45 ± 6 µM). A parallel fall (P < 0.05) in net hepatic glycerol uptake also occurred (2.0 ± 0.4 to 1.0 ± 0.2 vs. 2.0 ± 0.2 to 1.0 ± 0.3 µmol · kg-1 · min-1).


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Fig. 5.   Arterial blood lactate concentrations and net hepatic lactate uptake in infected (n = 7) and sham (n = 7) clot dogs receiving a primed continuous infusion of glucose into the duodenum. Data are expressed as means ± SE (per kg body wt, where applicable).



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Fig. 6.   Arterial blood alanine concentrations, net hepatic alanine output, and net hepatic alanine fractional extraction in infected (n = 7) and sham (n = 7) clot dogs receiving a primed continuous infusion of glucose into the duodenum. Data are expressed as means ± SE (per kg body wt, where applicable).

Hepatic glucose oxidation was 0.4 ± 0.1 vs. 0.5 ± 0.1 mg · kg-1 · min-1 during the last hour of the study. From liver biopsies obtained at the end of the study, tracer-determined glycogen synthesis was similar in both groups (1.3 ± 0.3 vs. 1.0 ± 0.3 mg · kg-1 · min-1); however, hepatic glycogen content was lower in the infected group (508 ± 59 vs. 312 ± 54 mg/kg body wt). The sum of tracer-determined hepatic glycogen deposition, lactate release, and glucose oxidation could account for 70 and 55% of the total carbon uptake in the sham and infected groups, respectively.


    DISCUSSION
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

In the present study, infection did not attenuate the increase in net hepatic glucose uptake seen when glucose was administered via the intraduodenal route. On the basis of our previous work, when glucose was infused via the peripheral route, infection decreased net hepatic glucose uptake (17). The normal liver glucose uptake during duodenal glucose infusion is even more surprising, given that infection delayed net intestinal glucose uptake. However, not all aspects of liver metabolism were normalized; the liver of the infected animal remained a net consumer of lactate, whereas the liver of the sham animal was not a consumer of lactate. These studies suggest that, despite infection-induced alterations in intestinal absorption, when glucose is administered via the oral (duodenal) route, the presence of infection does not impair net hepatic glucose uptake.

The infection-induced decrease in intestinal glucose absorption (down-arrow ~25%) after glucose infusion explained the attenuated rise in arterial blood glucose concentration in the infected animals. The decrease in net glucose absorption was caused by an impairment in unidirectional intestinal glucose output rather than by a stimulation of intestinal glucose utilization. The mechanism for this attenuation is unknown. Intestinal glucose absorption requires a sodium-dependent glucose transporter (SGLT1) (6). It is unclear whether the impairment in glucose absorption represents a specific impairment in SGLT1, a nonspecific impairment in sodium-coupled transport, or a more general defect in gut absorption. The latter could be caused by impairments in mucosal mass or mucosal blood flow or to increases in intestinal transit time (6). Although intestinal hyperpermeability to large macromolecules is suspected to occur during systemic infections (22), sepsis can delay the absorption of small molecules such as glucose (12).

Despite the blunted gut glucose absorption, net hepatic glucose uptake was not diminished by infection. The two determinants of liver glucose uptake in the normal setting are hepatic glucose load and net hepatic glucose fractional extraction. Hepatic glucose load is dependent on liver blood flow and glucose concentration. In our previous report (17), liver blood flow was not increased in this model of infection. In the present study, liver blood flow was increased by 30% in the infected group. We do not have an explanation for this difference; however, one possibility is that we used Transonic rather than Doppler flow probes in the present study. The Transonic flow probes are not subject to problems with turbulence and orientation of the probe with respect to the vessel. Regardless of the reason, an underestimation of liver blood flow cannot explain the differences in the two routes of administration. Recalculation of the previous data by use of the mean flow obtained in this study had minimal effects on the calculated net hepatic glucose uptake. This is because the primary contributor to the infection-induced alterations in liver glucose uptake during peripheral glucose infusion (17) was a marked decrease in net hepatic glucose fractional extraction.

Infection did not impair net hepatic glucose uptake when glucose was given intraduodenally, because net hepatic glucose fractional extraction was not altered. In the previous study, hepatic glucose uptake was decreased when glucose was given into a peripheral vein, because net hepatic glucose fractional extraction was markedly decreased by infection (17). The mechanism whereby duodenal glucose delivery overcame the defect in net hepatic glucose fractional extraction is unclear. It is well known that oral delivery of glucose enhances net hepatic glucose fractional extraction, and consequently net hepatic glucose uptake, to a greater extent than when the glucose is given into a peripheral vein (23). The enhancement of liver glucose uptake seen with the oral route does not require the gut; bypassing the gut by infusing the glucose directly into the portal vein mimics the response. The ability of portal delivery of glucose to augment liver glucose uptake has been termed the "portal signal" (23). Activation of the portal signal may be capable of overriding the infection-induced impairment in liver uptake and fractional extraction of glucose by the liver. Thus, although the mechanism by which the portal signal enhances liver glucose uptake is unknown, it is clear that some aspect of duodenal glucose delivery (possibly the portal signal) can play a dominant role in facilitating liver glucose uptake during infection.

The effective suppression of hepatic glucose production seen during intraduodenal glucose infusion contributed to the improved hepatic glucose disposal during infection. During a peripheral glucose infusion, the lack of suppression of hepatic glucose production was as important as the lack of stimulation of unidirectional hepatic glucose uptake in limiting net hepatic glucose uptake during infection (17). The inability of a peripheral infusion of exogenous glucose to suppress endogenous glucose production has been observed in stressed humans as well (26). It is unclear how intraduodenal infusion of glucose is more effective than peripheral glucose infusion in suppressing hepatic glucose production during infection.

Although hepatic glucose uptake was not altered by infection, the liver of the infected animal remained a net lactate consumer. In a normal animal, when the liver is a net consumer of glucose, the liver is either releasing lactate or at least is not consuming lactate, indicating that glycolysis is increased and gluconeogenesis from lactate is suppressed. However, during infection, the liver exhibited net lactate consumption, which may reflect a persistent stimulation of gluconeogenesis. In noninfected animals, the switch to lactate production is thought to reflect diversion of a portion of the glucose carbons to glycolysis. Chronic exposure to high cortisol concentrations amplifies glycolysis in the liver, but this can be reversed by excess glucagon (16). Thus hyperglucagonemia, a characteristic response to infection, may explain the maintenance of substantial lactate consumption in the face of normal hepatic glucose uptake.

Tracer-determined hepatic glycogen synthesis was also normal after intraduodenal glucose delivery. After peripheral glucose delivery, tracer-determined glycogen synthesis was decreased, primarily because of a decrease in net hepatic glucose uptake (17). Because liver glucose uptake was not impaired during duodenal glucose delivery, and because glycogen synthesis is a major fate for liver glucose uptake, it is not surprising that glycogen synthesis was normal. Some aspect of duodenal glucose delivery, possibly the portal signal, may have helped facilitate hepatic glycogen synthesis. Diversion of gluconeogenic carbon to glycogen (i.e., indirect glycogen synthesis) can amplify glycogen deposition. Indirect glycogen synthesis is significant even in the normal dog (20), and the tracer method we used does not distinguish between direct and indirect glycogen synthesis. Approximately 60% of the net glucose uptake could be accounted for by tracer-determined glycogen deposition in both groups. In the infected group, the liver remained a net hepatic lactate consumer; thus it is likely that indirect hepatic glycogen synthesis was amplified. Although hepatic glycogen content was greater in the sham group after glucose infusion, this does not mean that net glycogen synthesis was higher in the sham group. Without knowing the glycogen content before glucose infusion, net hepatic glycogen synthesis could not be calculated. However, it is likely that the hepatic glycogen content was lower in the infected group, which may have facilitated hepatic glycogen synthesis (9). Although previous work has demonstrated that glycogen synthesis is impaired by infection during peripheral glucose infusion (4), we found no evidence that it is impaired when glucose is given intraduodenally (2). The mechanism by which the portal signal activates hepatic glucose entry is unknown. It requires an intact hepatic neural supply, and it facilitates hepatic glycogen synthesis and lactate release in the normal animal (23). Thus it likely acts at an early point in the metabolic pathway such as activation of glucokinase (23). Generation of such a signal may be sufficient to normalize hepatic glucose entry during infection.

For the stressed patient, improving liver glucose uptake by delivering glucose via the enteral route may help limit the hyperglycemia associated with nutrient intake. This is most critical in individuals with preexisting glucose intolerance (19). By enhancing liver glucose uptake, the mass of glucose that has to be removed by the insulin-resistant peripheral tissues will be lessened. In turn, whole body insulin requirements may be lessened as well. Although enteral delivery is the preferred route of nutrient delivery, in part because of its trophic effects on the intestinal mucosal barrier (24, 28), the complications of malabsorption in the stressed patient have been an obstacle to its widespread use. The additional benefit of improved hepatic glucose disposal observed in this study further amplifies the need to overcome the complications associated with enteral feeding to achieve the multiple benefits of enteral nutrient delivery on intestine and hepatic function.

In summary, net hepatic glucose uptake is not decreased by infection when glucose is administered via the gastrointestinal route. This occurs despite delayed absorption of glucose by the gut during infection. The infection-induced enhancement in net hepatic lactate uptake persists, however, suggesting that oral glucose delivery cannot override the characteristic augmentation of gluconeogenesis.


    ACKNOWLEDGEMENTS

The authors are grateful for the technical assistance of Pamela Venson and Eric Allen from the hormone core laboratory of the Vanderbilt University Diabetes Research and Training Center.


    FOOTNOTES

This study was supported by National Institute of Diabetes and Digestive and Kidney Diseases Grant DK-43748 (O. P. McGuinness), with support from the Clinical Nutrition Research Center (DK-26657) and Diabetes Research and Training Center Grant P60-DK-20593.

Address for reprint requests and other correspondence: O. P. McGuinness, Dept. of Molecular Physiology and Biophysics, 702 Light Hall, Vanderbilt University, Nashville, TN 37232-0615 (E-mail: owen.mcguinness{at}mcmail.vanderbilt.edu).

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Received 29 November 1999; accepted in final form 2 February 2000.


    REFERENCES
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

1.   Aguilar-Parada, E, Eisentraut AM, and Unger RH. Pancreatic glucagon secretion in normal and diabetic subjects. Am J Med Sci 257: 415-419, 1969[ISI][Medline].

2.   Buday, AZ, Lang CH, Bagby GJ, and Spitzer JJ. Glycogen synthase and phosphorylase activities during glycogen repletion in endotoxemic rats. Circ Shock 19: 149-163, 1986[ISI][Medline].

3.   Chan, TM, and Exton JH. A method for the determination of glycogen content and radioactivity in small quantities of tissues or isolated hepatocytes. Anal Biochem 71: 96-105, 1976[ISI][Medline].

4.   Curnow, RT, Rayfield EJ, George DT, Zenser TV, and DeRubertis FR. Altered hepatic glycogen metabolism and glucoregulatory hormones during sepsis. Am J Physiol 230: 1296-1301, 1976[ISI][Medline].

4a.   Debodo, RC, Steele R, Alszuler N, Dunn A, and Bishop JS. On the hormonal regulation of carbohydrate metabolism: studies with 14C glucose. Recent Prog Horm Res 19: 445-488, 1963[ISI].

5.   Farmer, RW, and Pierce C. Plasma cortisol determination: radioimmunoassay and competitive protein binding compared. Clin Chem 20: 411-414, 1974[Abstract/Free Full Text].

6.   Ferraris, RP, and Diamond J. Regulation of intestinal sugar transport. Physiol Rev 77: 257-302, 1997[Abstract/Free Full Text].

7.   Fink, MP, MacVittie TJ, and Casey LC. Inhibition of prostaglandin synthesis restores normal hemodynamics in canine hyperdynamic sepsis. Ann Surg 200: 619-626, 1984[ISI][Medline].

8.   Fredrickson, DS, and Ono K. An improved technique for assay of 14CO2 in expired air using the liquid scintillation counter. J Lab Clin Med 51: 147-151, 1958[ISI].

9.   Galassetti, P, Hamilton KS, Gibbons FK, Bracy DP, Lacy DB, Cherrington AD, and Wasserman DH. Effect of fast duration on the disposition of an intraduodenal glucose load in the conscious dog. Am J Physiol Endocrinol Metab 276: E543-E552, 1999[Abstract/Free Full Text].

10.   Goldstein, SA, and Elwyn DH. The effects of injury and sepsis on fuel utilization. Annu Rev Nutr 9: 445-473, 1989[ISI][Medline].

11.   Gump, FE, Long C, and Killian P. Studies of glucose intolerance in septic injured patients. J Trauma 14: 378-388, 1974[ISI][Medline].

12.   Johnston, JD, Harvey CJ, Menzies IS, and Treacher D. Gastrointestinal permeability and absorptive capacity in sepsis. Crit Care Med 24: 1144-1149, 1996[ISI][Medline].

13.   Lloyd, B, Burrin J, Smythe P, and Alberti KGMM Enzymatic fluorometric continuous flow assays for blood glucose, lactate, pyruvate, alanine, glycerol and 3-hydroxybutyrate. Clin Chem 24: 1724-1729, 1978[Abstract/Free Full Text].

14.   Macdonald, IA, and Lake DM. An improved technique for extracting catecholamines from body fluids. J Neurosci Methods 13: 239-248, 1985[ISI][Medline].

15.   McGuinness, OP. The impact of infection on gluconeogenesis in the conscious dog. Shock 2: 336-343, 1994[ISI][Medline].

16.   McGuinness, OP, Burgin K, Moran C, Bracy D, and Cherrington AD. Role of glucagon in the metabolic response to stress hormone infusion in the conscious dog. Am J Physiol Endocrinol Metab 266: E438-E447, 1994[Abstract/Free Full Text].

17.   McGuinness, OP, Jacobs J, Moran C, and Lacy DB. Impact of infection on hepatic disposal of a peripheral glucose infusion in the conscious dog. Am J Physiol Endocrinol Metab 269: E199-E207, 1995[Abstract/Free Full Text].

18.   McGuinness, OP, Lacy DB, and Anderson J. Effect of acute glucagon removal on metabolic response to infection in conscious dog. Am J Physiol Endocrinol Metab 268: E92-E99, 1995[Abstract/Free Full Text].

19.   McMahon, MM, and Rizza RA. Nutrition support in hospitalized patients with diabetes mellitus. Mayo Clin Proc 71: 587-594, 1996[ISI][Medline].

20.   Moore, MC, Cherrington AD, Cline G, Pagliassotti MJ, Jones EM, Neal DW, Badet C, and Shulman GI. Sources of carbon for hepatic glycogen synthesis in the conscious dog. J Clin Invest 88: 578-587, 1991[ISI][Medline].

21.   Myers, SR, McGuinness OP, Neal DW, and Cherrington AD. Intraportal glucose delivery alters the relationship between net hepatic glucose uptake and the insulin concentration. J Clin Invest 87: 930-939, 1991[ISI][Medline].

22.   O'Dwyer, ST, Michie HR, Zeigler TR, Revhaug A, Smith RJ, and Wilmore DW. A single dose of endotoxin increases intestinal permeability in healthy humans. Arch Surg 123: 1459-1464, 1988[Abstract].

23.   Pagliassotti, MJ, and Cherrington AD. Regulation of net hepatic glucose uptake in vivo. Annu Rev Physiol 54: 847-860, 1992[ISI][Medline].

24.   Saito, H, Trocki O, Alexander JW, Kopcha R, Heyd T, and Joffe SN. The effect of route of nutrient administration on the nutritional state, catabolic hormone secretion, and gut mucosal integrity after burn injury. J Parenter Enteral Nutr 11: 1-7, 1987[Abstract].

25.   Shaw, JHF, Klein S, and Wolfe RR. Assessment of alanine, urea and glucose interrelationships in normal subjects and in patients with sepsis with stable isotopes. Surgery 97: 557-567, 1985[ISI][Medline].

26.   Shaw, JH, and Wolfe RR. Response to glucose and lipid infusions in sepsis: a kinetic analysis. Metabolism 34: 442-449, 1985[ISI][Medline].

26a.   Wall, JS, Steele R, Debodo RC, and Altszuler N. Effect of insulin on utilization and production of circulating glucose. Am J Physiol 189: 43-50, 1957[ISI].

27.   Wide, L, and Porath J. Radioimmunoassay of proteins with the use of Sephadex-coupled antibodies. Biochem Biophys Acta 130: 257-260, 1966[ISI].

28.   Ziegler, TR, Gatzen C, and Wilmore DW. Strategies for attenuating protein-catabolic responses in the critically ill. Annu Rev Med 45: 459-480, 1994[ISI][Medline].


Am J Physiol Endocrinol Metab 279(1):E108-E115
0193-1849/00 $5.00 Copyright © 2000 the American Physiological Society




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