Kupffer Cell Phagocytosis Research Articles

Pertussis toxin-induced redistribution of cortical actomyosin and inhibition of phagocytosis in rat Kupffer cells.

The mechanism of phagocytosis by Kupffer cells has been shown to be related to the Ca(2+)-calmodulin and the actomyosin systems. However the role of the transmembrane signal transmitter, G-protein, is still unknown. In this study, a quantitative evaluation of phagocytosis by Kupffer cells of rats in culture and the effects of pertussis toxin, a G-protein inhibitor, on the phagocytic function and morphology of Kupffer cells were investigated. Pertussis toxin inhibited phagocytosis of Kupffer cells with dysfunction of the actomyosin system. The inhibitory effects of pertussis toxin suggest that G-protein may be involved in the mechanism of transmembrane signalling in phagocytosis by Kupffer cells.

Vitamin A Potentiation of Carbon Tetrachloride Hepatotoxicity: Role of Liver Macrophages and Active Oxygen Species

Pretreatment of rats with large doses of vitamin A (VA) potentiates the hepatotoxicity of CCl 4. Because our previous studies indicate that VA treatment does not enhance CCl 4, metabolism but does enhance CCl 4-induced lipid peroxidation and activates liver Kupffer cells to release increased amounts of oxygen-centered free radicals, the current studies were designed to determine if VA treatment potentiates CCl 4-induced liver injury through increased release of reactive oxygen species. Plasma clearance of colloidal carbon, an index of Kupffer cell phagocytic activity, was enhanced two- to threefold in rats treated for 7 days with VA (retinol, 250,000 IU/kg per day). Accordingly, VA treatment alone caused Kupffer cell activation. To determine if these activated Kupffer cells could potentiate hepatic injury through release of reactive oxygen species upon Cd4 challenge, polyethylene glycol coupled-superoxide dismutase (PEG-SOD, 10,000 IU/kg) or -catalase (PEG-CAT, 40,000 IU/kg) was given iv 2 hr after CCl 4, (0.15 ml/kg, ip) to control or VA-pretreated rats to quench any released reactive oxygen. PEG-SOD and PEG-CAT effectively blocked VA potentiation of CCl 4, liver injury as assessed at 24 hr by change in plasma ALT. Methylpalmitate (MP, 2 g/kg), an inhibitor of Kupffer cell phagocytosis and related oxygen burst, also blocked the potentiation of liver injury when given iv 24 hr before CCI4 to VA-pretreated rats. At the doses used, PEG-SOD or PEG-CAT did not influence CCl 4 toxicity in control rats (at 0.15 or 2 ml CCl 4/kg). Importantly, SOD, CAT, and MP blocked the enhanced lipid peroxidation induced by CCl 4, in VA-pretreated rats. From these findings we conclude that the potentiation of CCl 4, liver injury by VA pretreatment is mediated, at least in part, by active oxygen species released from Kupffer cells and possibly other macrophages that are activated by VA. Supporting this conclusion is the failure of VA pretreatment to increase the release of LDH from suspension of hepatocytes incubated with CCl 4,.

Influence of Kupffer cell phagocytosis blockade on the production of ovalbumin-specific IgE and IgG1 antibodies in an experimental model.

The aim of the present study was to evaluate the influence of Kupffer cell phagocytosis blockade (KCPB) on the production of reaginic (IgE) and non-reaginic (IgG1) ovalbumin antibodies in an experimental animal model. Forty-two female heterozygous Gunn rats were injected with two 100 micrograms doses of ovalbumin separated by 13 days, into jugular vein (Group I, n = 10), portal vein (Group II, n = 10), jugular vein with prior KCPB (Group III, n = 10) and portal vein with prior KCPB (Group IV, n = 12). KCPB was induced with gadolinium chloride (5 mg/kg body weight, 24 hr before each ovalbumin administration). Antibodies were determined by passive cutaneous anaphylaxis in sera obtained 12 days after the first dose of ovalbumin and 8 days after the second one. No antibodies were detected at any time in Group II. The maximum response was observed in Group IV in which, after two doses of ovalbumin, 100% of the animals presented IgG1 and 58% presented detectable IgE antibodies. Differences between group IV and the other groups were statistically significant. This phenomenon does not seem to be due to a systemic effect of gadolinium chloride since humoral response was not increased in Group III with respect to Group I. It is concluded that the liver represents a barrier to IgE and IgG1 sensitization. KCPB not only eliminates this barrier, but also clearly increases antibody production to a protein antigen (ovalbumin) arriving at the liver through the portal vein.

ETHANOL AND DIET-INDUCED ALTERATIONS IN KUPFFER CELL FUNCTION

The effects of 6 weeks of alcohol feeding on phagocytic, metabolic and secretory functions as well as gene expression of hepatic Kupffer cells were evaluated in vitro using cultured Kupffer cells isolated from male Sprague-Dawley rats. The rats were fed either Teklad pelleted rat chow or the 1982 Lieber-DeCarli liquid diet containing 6% ethanol (36% calories) or the same liquid diet with maltose-dextrin isocalorically substituted for the alcohol. Weight gain was greatest in the chow-fed animals and least in those receiving ethanol. The alcohol-containing diet stimulated Kupffer cell phagocytosis, mitochondrial reduction of MTT, secretion of tumor necrosis factor (TNF) and expression of TNF mRNA. However, each of these cell functions was also enhanced by the control Lieber-DeCarli liquid diet alone and the stimulating effect of the control diet often exceeded that induced by ethanol. The results suggest that early in chronic alcohol consumption, the immune system may be stimulated by ethanol, and that during studies of ethanol-induced changes in immune system function, close attention must be given to potentially confounding effects of the diet.

Perfluorochemical emulsions decrease Kupffer cell phagocytosis

One drawback to using perfluorochemical emulsions as blood substitutes is that perfluorochemical particles are cleared from the blood by the reticuloendothelial system, primarily liver and spleen. We measured the impact of two perfluorochemical emulsions on clearance of colloidal carbon (less than 1 microns) and 51Cr-sheep red blood cells (about 8 microns) by the reticuloendothelial system in vivo and in the isolated perfused liver. Male rats were injected with 2 ml/100 gm body wt of Fluosol-DA or Oxypherol-ET for 4 consecutive days. Carbon (1 ml/100 gm body wt) or sheep red blood cells (0.05 ml of 5% vol/vol/100 gm body wt) were then injected intravenously (in vivo) or added to perfusate. Samples were taken at several time points for 1 hr. In the isolated perfused liver, carbon clearance was depressed by 25% 1 day after treatment. Rates returned to control levels by 12 days in Fluosol-DA-treated rats but remained depressed by 67% in Oxypherol-ET-treated rats. Sheep red blood cell (8 microns) clearance was two to five times slower than carbon clearance and depressed by 40% in livers from Fluosol-DA rats 1 day and 12 days after treatment. Added serum did not improve phagocytosis. In vivo carbon clearance remained normal in Fluosol-DA-treated rats but decreased by 74% in Oxypherol-ET-treated rats 1 day after treatment, returning to normal by 12 days. Clearance rates were similar in control rats in vivo and in the perfused liver. We conclude that the isolated perfused liver is a good model to measure liver clearance function. Although low doses of perfluorochemical emulsions may depress Kupffer cell phagocytosis, general reticuloendothelial system function is not significantly compromised.

A new method to monitor Kupffer cell phagocytosis continuously in perfused rat liver

A new method to monitor Kupffer cell phagocytosis continuously in perfused rat liver

A new method to monitor Kupffer cell phagocytosis continuously in perfused rat liver

A new method was developed to monitor Kupffer cell phagocytosis continuously in perfused liver using a fluorescent probe, rhodamine-gelatin, synthesized from gelatin and rhodamine isothiocyanate. In perfused rat liver, phagocytosis by Kupffer cells was assessed both by uptake of the dye and from fluorescence measured from the liver surface. Uptake of rhodamine-gelatin and surface fluorescence (520----585 nm) increased as perfusate concentrations of rhodamine-gelatin were elevated. Histological examination revealed that fluorescence caused by rhodamine-gelatin was concentrated in cells lining the sinusoid. Furthermore, when hepatic parenchymal, endothelial and Kupffer cells were isolated by centrifugal elutriation after pretreatment in vivo with rhodamine-gelatin, the fluorescent label was detected nearly exclusively in the Kupffer cell fraction. Fluorescence of rhodamine-gelatin from the liver surface was directly proportional to uptake of rhodamine-gelatin, indicating that measurement of surface fluorescence could be used as an index of phagocytic activity of Kupffer cells. Uptake of rhodamine-gelatin and fluorescent labeling of sinusoidal cells were inhibited nearly completely by dextran sulfate, which decreases phagocytic activity, and were increased by about 50% by pretreatment with endotoxin, which stimulates phagocytosis. This new method was combined with standard procedures to monitor parenchymal cell function (e.g., oxygen uptake and release of lactate dehydrogenase), Kupffer cell phagocytic activity and parenchymal cell injury simultaneously during perfusion with the hepatotoxicant allyl alcohol. Activation of phagocytosis by Kupffer cells monitored by rhodamine-gelatin fluorescence occurred within 5 min of addition of allyl alcohol. On the other hand, parenchymal cell injury, assessed from release of lactate dehydrogenase, did not begin until 40 min and reached maximal values at around 90 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of reticuloendothelial blockade on tissue distribution of 99mTc-labeled synthetic liposomes in ehrlich solid tumor-bearing mice.

The effect of a reticuloendothelial blockade was examined on the tissue distribution of 99mTc-labeled synthetic liposomes prepared from N,N-didodecyl-N alpha-[6-(trimethylammonio)hexanoyl]-L-alaninamide bromide (N+C5Ala2C12) in Ehrlich solid tumor-bearing mice. While a pre-dose of unlabeled phosphatidyl choline liposomes (natural liposomes) hardly influenced the tissue distribution of N+C5Ala2C12 liposomes, the pretreatment of dextran sulfate depressed the uptake in liver accompanied by increasing that in tumor and other tissues except the stomach. However, the extent of liver depression of N+C5Ala2C12 liposomes by dextran sulfate was lower than that of natural liposomes and the pre-dose of unlabeled natural liposomes had a minor effect on the tissue distribution of N+C5Ala2C12 liposomes compared with that of natural liposomes. In the liver uptake of N+C5Ala2C12 liposomes, it was suggested that Kupffer cell phagocytosis was not the main mechanism.

Kupffer cell blockade prevents induction of portal venous tolerance in rat cardiac allograft transplantation

Pretransplant portal venous (pv) administration of donor antigen induces allospecific partial tolerance. Although the involved mechanism has not been defined, antigen presentation by Kupffer cells (KC) in the liver is considered to be critical. We evaluated the effect of KC blockade on this pv tolerance induction in Buffalo (RT1 6) rats receiving Lewis (RT1 1) cardiac heterotopic allografts. Control rats received no treatment, while experimental animals received 25 × 10 8 ultraviolet B-irradiated (12,000 J/m 2) donor spleen cells via either the iv (systemic intravenous) or the pv routes 7 days before transplantation. Gadolinium chloride (GdCl 3), a rare earth metal known to inhibit KC phagocytosis, was given (7 mg/kg) 1 and 2 days before pv preimmunization. Cardiac graft prolongation was obtained by pv (MST = 13.3 ± 1.9 days, n = 6, vs control = 7.3 ± 0.5 days, n = 6; P < 0.001) but not by iv preimmunization (7.7 ± 0.7 days, n = 6, NS vs control). KC blockade abolished the pv tolerance, as indicated by abrogation of graft prolongation (PV + GdCl 3 = 8.0 ± 0.8 days, n = 6, NS vs control). These findings suggest that effective alloantigen uptake by KC in the liver is essential for the induction of pv tolerance in rat cardiac transplantation.

Kupffer Cell Blockade Increases Mortality During Intra-abdominal Sepsis Despite Improving Systemic Immunity

The effect of Kupffer cell (KC) blockade on systemic immunity during intra-abdominal sepsis was evaluated. Gadolinium chloride, a rare earth metal, reduced KC phagocytosis by 75% when it was given to BALB/c mice for 2 days. Thereafter, control mice and mice with KC blockade underwent either a sham operation or a cecal ligation and puncture. As indicators of systemic cell-mediated immunity, delayed-type hypersensitivity responses to soluble antigen and cellular alloantigen were measured 24 hours after the abdominal operations. The activation of KCs was assessed by their in vitro interleukin 1 production. Control septic mice were profoundly immunosuppressed and demonstrated marked KC activation. Septic mice with KC blockade, however, demonstrated less systemic immune hyporesponsiveness and significantly reduced KC activation, but died more rapidly. We concluded that despite apparent improvement in systemic immunity by KC blockade during intra-abdominal sepsis, the resulting impairment in functional phagocytic integrity predisposes to significantly higher mortality.

Alteration of rat Kupffer cell function following mitomycin-C administration.

Cancer chemotherapeutic agents modify the human immune system in diverse ways including both immunosuppression and immunostimulation. We evaluated the effects of mitomycin-C on rat Kupffer cell phagocytosis, C3b receptor binding, and lysosomal enzyme activity. Kupffer cell cultures were greater than 95% pure. Phagocytosis of IgG-coated sheep red blood cells was demonstrated by 84% of control cells but by only 25% of cells isolated two weeks following mitomycin-C administration (p less than 0.0005). This depression in phagocytic ability had returned to control levels by four weeks posttreatment. Similarly, C3b receptor binding of IgM and complement coated sheep red blood cells was observed in 88% of control Kupffer cells, but declined to 47% at two weeks after drug administration (p less than 0.005) and returned to normal after four weeks. Lysosomal enzyme activity was not impaired by mitomycin-C. Histologically severe ulceration of the colon of treated animals was seen one and two weeks after drug administration, but healed by four weeks post-mitomycin-C treatment. Depression of macrophage function as a consequence of cancer chemotherapy may have important clinical consequences in host defense against bacteria and tumor metastases.

Effect of Kupffer cell phagocytosis of erythrocytes and erythrocyte ghosts on susceptibility to endotoxemia and bacteremia.

The phagocytosis of erythrocytes by macrophages has previously been shown to depress macrophage function. In this study we compared the effect of the phagocytosis of erythrocytes and erythrocyte ghosts by Kupffer cells on the duration of the depression of complement receptor clearance function and host defense against endotoxemia and bacteremia. Phagocytosis of erythrocytes and erythrocyte ghosts was induced in rats by the injection of rat erythrocytes or erythrocyte ghosts coated with anti-rat erythrocyte immunoglobulin G (EIgG and GIgG, respectively). The hepatic uptake of EIgG and GIgG (17.4 X 10(8)/100 g) occurred during the first 30 min after injection. The digestion of phagocytized EIgG and GIgG, as assessed by electron microscopy, was complete at 24 and 3 h after injection, respectively. The depression of Kupffer cell complement receptor clearance function caused by EIgG and GIgG returned to normal by 6 h after injection of EIgG and by 3 h after injection of GIgG. Phagocytosis of EIgG depressed the survival rate after endotoxemia and bacteremia when endotoxin or bacteria were injected at 30 min after EIgG. The survival rate returned to normal when the endotoxin and bacteria were injected at 12 and 6 h after the EIgG, respectively. Phagocytosis of GIgG did not depress the survival rate after endotoxemia and bacteremia. Thus, compared with erythrocytes, erythrocyte ghosts are more rapidly digested after phagocytosis, depress complement receptor function for a shorter period of time, and cause less depression of host defense. These findings indicate that the contents of erythrocytes play an important role in the impairment of host defense caused by the phagocytosis of erythrocytes by Kupffer cells.

Potential role of activated macrophages in acetaminophen hepatotoxicity: II. Mechanism of macrophage accumulation and activation

Treatment of rats with acetaminophen (1.2 g/kg) results in the accumulation of activated macrophages in the centrilobular regions of the liver. To study the mechanism by which these cells accumulate and become activated, we examined the release of chemotactic and activating factors from cultured hepatocytes treated with acetaminophen (10–100 μ m). We found a dose- and time-related generation of Kupffer cell and monocyte chemotactic activity by acetaminophen-treated hepatocytes. The maximum response was observed with a 25% dilution of medium collected 24 hr following treatment of hepatocytes with acetaminophen. Using a checkerboard assay, the factor in conditioned medium was determined to induced chemotaxis as well as chemokinesis in both Kupffer cells and monocytes. The hepatocyte-derived chemotactic factor was also found to be stable to freeze-thawing but to lose activity following heat or trypsin treatment. These results, together with our findings that chemotactic activity was eluted in the void volume following Sephadex G-25 size exclusion chromatography, suggested that the chemotactic factor released by hepatocytes is a large molecular weight protein. The release of Kupffer cell activating factors by acetaminophen-treated hepatocytes was also examined. Hepatocyte-conditioned medium was found to stimulate Kupffer cell phagocytosis and superoxide anion release, two characteristics of activated macrophages. These effects were maximal with conditioned medium collected from hepatocytes 24 hr following treatment with 50–100 μ m acetaminophen. Acetaminophen alone had no effect on chemotaxis, phagocytosis, or superoxide anion production by Kupffer cells or monocytes. Taken together, these results suggest that macrophage accumulation and activation in the liver following acetaminophen treatment may be mediated, at least in part, by factors released from hepatocytes.

Phagocytosis, an unrecognized property of murine endothelial liver cells.

Impairment of the phagocytic capacities of Kupffer cells, as is found in Frog Virus 3 hepatitis of mice, allows the endothelial liver cells to take up intravenously inoculated latex particles of 1.0 micron diameter. In vitro experiments with cultivated endothelial cells isolated by collagenase perfusion of the liver and purified by centrifugal elutriation demonstrate that uptake occurs via a typical mechanism of phagocytosis involving pseudopodia. Ingestion of latex is inhibited by incubation of the cells at 4 degrees C and by treatment with cytochalasin B, whereas colchicine has no effect. These results demonstrate that: the Kupffer cells are not the only cells of the hepatic sinusoid capable of phagocytosis; and under conditions where the phagocytosis in Kupffer cells is impaired, the endothelial cells may participate in the clearance of large particles from the blood.

Deficient Kupffer cell phagocytosis and lysosomal enzymes in the endotoxin-low-responsive C3H/HeJ mouse.

Various substances, including lysosomal enzymes, are produced by Kupffer cells and other macrophages; their release has been implicated in the toxic response to endotoxins. C3H/HeJ mice exhibit little or no response to doses of endotoxin that are lethal in syngeneic C3HeB/FeJ mice. To explore the nature of this deficient response, the Kupffer cells of these mice were studied using in vivo microscopic as well as histochemical and electron microscopical methods. In vivo, the rate of phagocytosis of single 0.8 micron latex particles was measured in individual Kupffer cells as was the number of phagocytic cells per microscopic field. Frozen sections of livers were stained for a variety of lysosomal enzymes and liver specimens also were processed for electron microscopy. In comparison to the endotoxin-sensitive C3HeB/FeJ mice, the livers of the C3H/HeJ mice contained 60% fewer Kupffer cells that phagocytosed latex. However, the rate of phagocytosis by these cells was not statistically different and ranged from 19-26 sec. The volume density of acid-phosphatase-positive Kupffer cells was 40% less in the C3H/HeJ mice. Similar differences were observed with other lysosomal enzymes including cathepsins B and H and dipeptidyl peptidases I and II. However, light and electron microscopy revealed a relatively normal number of Kupffer cells in livers stained for peroxidase, a nonlysosomal enzyme. The results suggest that the insensitivity of C3H/HeJ mice to endotoxin may be related in part to a lysosomal enzyme deficiency and a paucity of phagocytic Kupffer cells in these animals.

Actin-induced reticuloendothelial phagocytic depression as mediated by its interaction with fibronectin

Circulating fibronectin, also known as opsonic α 2 surface binding glycoprotein or coldinsoluble globulin, modulates phagocytosis of tissue debris, fibrin microaggregates, and gelatin-coated colloids by the reticuloendothelial (RE) system. Opsonically active fibronectin has an actin binding site and a demonstrated in vitro affinity for actin. Since actin potentially released into blood and tissue fluids following tissue injury could complex with fibronectin, the present study evaluated the effect of actin on plasma opsonic activity and Kupffer cell phagocytosis. Intravenous injection of actin did not acutely decrease plasma immunoreactive fibronectin levels although fibronectin levels increased at 6, 12, and 24 hr postinjection. However, intravenous actin injection did depress RE phagocytic activity in vivo as measured by decreased blood clearance of test colloid and impaired hepatic uptake of colloid particles as well as retention of the particles in the circulation. In vitro, preincubation of plasma with actin depressed the opsonic activity of plasma with respect to its ability to support phagocytosis, but such treatment of plasma did not alter the detection of fibronectin by immunoassay. Utilizing purified fibronectin with demonstrated opsonic activity, it was also observed that actin interaction with fibronectin would block its biological ability to enhance phagocytosis. This effect appeared to be mediated at the humoral level, since no direct depressant effect of actin on Kupffer cell function was observed. Thus, actin, if released into the blood following injury, may contribute to bioassayable opsonic fibronectin deficiency and phagocytic dysfunction, but this disturbance would remain undetectable by immunoassay of fibronectin levels.

Role of the Liver in Endotoxin–Induced Hyperinsulinemia and Hyperglucagonemia in Rats

The intravenous administration of bacterial endotoxin to fasted rats elicited basal portal and systemic venous hyperinsulinemia and hyperglucagonemia. Enhanced pancreatic secretion of insulin and glucagon was implied by the elevated portal venous hormonal levels. Elevated insulin and glucagon levels were present at 4 hr after a 33 micrograms/100 gm intravenous endotoxin dose despite no fluctuation of the plasma glucose concentration. The role of the liver in the pancreatic hormonal response to endotoxin was investigated by infusing lipopolysaccharide slowly into the portal vein or systemic inferior vena cava. At doses of 33 and 100 micrograms per 100 gm, endotoxin administered via the systemic route stimulated significantly greater insulin and glucagon responses than did portal administration. Furthermore, rats with acute liver injury induced by partial (67%) hepatectomy, which depressed Kupffer cell phagocytosis, did respond to the 33 micrograms per 100 gm intraportal endotoxin dose with significantly greater hyperinsulinemia and hyperglucagonemia. These data suggest that hepatic Kupffer cells normally function to remove lipopolysaccharide from the portal venous blood and that at least at low pharmacological doses the pancreatic hormonal response to endotoxin is mediated by an unknown systemic mechanism.

The effect of reticuloendothelial blockade on the blood clearance and tissue distribution of liposomes

The blood clearance and tissue distribution of liposomes have been studied in mice subjected to reticuloendothelial blockade with dextran sulphate or carbon. The liposomes have been labelled in the lipid membranes with [ 3H]-cholesterol, [ 14C]phosphatidylcholine and/or 99mTc and the content with [ 14C]inulin. Reticuloendothelial blockade has been shown to slow the rate of clearance of neutral, positively and negatively charged liposomes and of both small unilamellar vesicles and large multimellar vesicles. In normal animals, the liver uptake accounted for only 20–55% of the total injected radioactivity, the amount varying with the charge and size of the liposomes. Following blockade, the liver uptake of charged and neutral multilamellar liposomes was depressed. This was also true for negatively charged small unilamellar vesicles. The degree of depression of hepatic uptake was between 25–50%, which contrasts with the 80–90% reduction in uptake of a wholly phagocytosed particle (sheep red cells). This difference suggests that mechanisms other than Kupffer cell phagocytosis are also responsible for the normal uptake of liposomes into the liver. In the case of neutral and positively charged small unilamellar vesicles, delayed clearance due to blockade was not associated with ‘depressed’ hepatic uptake. The site of action of blockading agents for these preparations is not clear. With all preparations of liposomes, blockade produced a slight and variable increase in uptake in the lung and spleen. The alteration of distribution of liposomes by reticuloendothelial blockade is therefore not great and the value of the technique in modifying the tissue distribution of substances within liposomes may be limited.

Kupffer cell phagocytosis in relation to BSP clearance in liver and inflammatory bowel diseases.

Experience using microaggregated human serum albumin for a Kupffer cell phagocytic capacity "stress test" in patients with liver and inflammatory bowel diseases is described. Each result has been related to a 1-hr BSP clearance in order to account for variations in liver blood flow. Kupffer cell clearances are reduced in proportion to BSP clearance in obstructive jaundice and in secondary biliary cirrhosis but are increased in patients with chronic hepatocellular inflmmation. Conversely Kupffer cell phagocytosis is often depressed in patients with alcoholic hepatitis. In Crohn's disease or ulcerative colitis RES function is normal unless patients are receiving corticosteroid suppression.

Mechanisms of acute hyperinsulinemia after Kupffer cell phagocytosis.

Blockade of hepatic Kupffer cells by prior phagocytosis of a variety of particulate materials caused acute hyperinsulinemia in glucose-stimulated fasted rats under pentobarbital anesthesia. At 4-h postblockade a 125-250% increase in peripheral plasma insulin levels occurred due to a combination of enhanced pancreatic insulin secretion and depressed hepatic insulin extraction. Enhanced pancreatic insulin secretion was confirmed by a 36-54% elevation of portal venous insulin levels. Depressed hepatic insulin extraction was indicated by a 37-47% reduction in insulin uptake by in situ perfused livers as well as alterations in portal-hepatic venous insulin differences and intravenous insulin tolerance tests in vivo. All parameters began to return toward control values at 24 and 48 h postblockade. Return was slow after inert carbon phagocytosis and rapid after degradable bacteria phagocytosis. Peripheral plasma insulin levels were very highly correlated with glucose clearance rates in all groups both control and experimental. Mechanisms are proposed to explain these findings based on the release of lysosomal enzymes and endogenous pyrogens by phagocytizing Kupffer cells as well as the presence of insulin receptors on hepatocytes and Kupffer cells.