Hepatic microcirculation in fatty liver disease.

Nonalcoholic fatty liver disease (NAFLD), the most common cause of steatosis, is associated with visceral obesity and insulin resistance. With more severe risk factors (obesity, type 2 diabetes [T2D], metabolic syndrome), steatosis may be complicated by hepatocellular injury and liver inflammation (steatohepatitis or NASH). NASH can lead to perisinusoidal fibrosis and cirrhosis. Fat-laden hepatocytes are swollen, and in steatohepatitis, further swelling occurs due to hydropic change (ballooning) of hepatocytes to cause sinusoidal distortion, as visualized by in vivo microscopy, reducing intrasinusoidal volume and microvascular blood flow. Involvement of other cell types (sinusoidal endothelial cells, Kupffer cells, stellate cells) and recruitment of inflammatory cells and platelets lead to dysregulation of microvascular blood flow. In animal models, the net effect of such changes is a marked reduction of sinusoidal space (approximately 50% of control), and a decrease in the number of normally perfused sinusoids. Such microvascular damage could accentuate further liver injury and disease progression in NASH. The fatty liver is also exquisitely sensitive to ischemia-reperfusion injury, at least partly due to the propensity of unsaturated fatty acids to undergo lipid peroxidation in the face of reactive oxygen species (ROS). This has important clinical consequences, particularly limiting the use of fatty donor livers for transplantation. In this review, we discuss available data about the effects of steatosis and steatohepatitis on the hepatic microvascular structure and sinusoidal blood flow, highlighting areas for future investigation.

Serum collagen type VI and XIV and hyaluronic acid as early indicators for altered connective tissue turnover in alcoholic liver disease.

Hepatic fibrosis in alcoholic liver disease often heralds progression to cirrhosis and, therefore, noninvasive parameters are required for early diagnosis and follow-up. Collagens VI and XIV, procollagen-III-N-propeptide, hyaluronic acid, and active transforming growth factor-beta1 (TGF-beta1) were measured in healthy volunteers, patients with alcoholic cirrhosis, and heavy drinkers without cirrhosis. Noncirrhotic alcoholics were assigned to two groups with either normal aspartate aminotransferase or levels > or = 2 normal. Collagens VI and XIV were elevated in all alcoholic patients compared to controls (P < 0.0001, all instances). Procollagen-III-N-propeptide and hyaluronic acid levels were higher in alcoholic patients with elevated liver enzymes and in cirrhotics as compared to controls. Procollagen-III-N-propeptide revealed a significant correlation with serum levels of TGF-beta1 (P < 0.0001). Collagens VI, and XIV, procollagen-III-N-propeptide, and hyaluronic acid appear to be sensitive markers indicating fibrotic transformation in alcoholics. The correlation between procollagen-III-N-propeptide and TGF-beta1 emphasizes its role in hepatic fibrogenesis.

Edward H. Bloch, M.D., Ph.D. Pioneer in the microscopic study of, and the microcirculation of, living tissues and organs.

Edward H. Bloch, M.D., Ph.D., Professor Emeritus of Anatomy, School of Medicine, Case Western Reserve University, died 3 November 2000 in Cleveland, Ohio at the age of 86. Known to his friends as "Maxl," he will be greatly missed by his friends, colleagues and former students.

Endotoxin, endotoxin-neutralizing-capacity, sCD14, sICAM-1, and cytokines in patients with various degrees of alcoholic liver disease.

BACKGROUND: Chronic alcohol ingestion leads to endotoxemia which is believed to play an important role in the pathogenesis of alcoholic liver disease (ALD). The purpose of this study was to determine if chronic ethanol consumption, in addition to affecting plasma endotoxin and cytokines, also affects the endotoxin-neutralizing capacity (ENC), sCD14, and sICAM-1, in patients with ALD. A second aim was to identify correlations between these latter parameters, endotoxin, and cytokines, especially IL-10. METHODS: Hospitalized patients with various degrees of ALD (n = 59), and 20 healthy volunteers were studied. Plasma endotoxin and ENC were determined using our kinetic Limulus amebocyte lysate test. Cytokines, sCD14, and sICAM-1 were measured by enzyme-linked immunosorbent assay. RESULTS: Patients with ALD exhibited a mild endotoxemia (p < 0.01) and a marked decrease in ENC (p < 0.0002). TNF-alpha (p < 0.05), IL-6 (p < 0.0001), sICAM (p < 0.005), and sCD14 (p < 0.0005) were significantly elevated in all patients with ALD, and IL-10 (p < 0.05) in patients with cirrhotic ALD. With the exception of IL-10, the cytokines correlated with each other and with sICAM-1. No correlations occurred between endotoxin, ENC, and sCD14, and between these and the cytokines and sICAM-1. Elevated levels of endotoxin correlate with acute excessive alcohol ingestion. No gender differences were observed. CONCLUSIONS: Acute alcohol intoxication rather than severe ALD results in significant endotoxemia. The limited capacity of plasma to neutralize endotoxin in liver injury seems to be an important factor in ALD which may be responsible for the release of endotoxin-induced mediators, such as cytokines, as well as s-ICAM-1, that are relevant in the pathogenesis of ALD.

Biliary obstruction exacerbates the hepatic microvascular inflammatory response to endotoxin.

Gram-negative sepsis is a serious complication for patients with obstructive jaundice. The present study was conducted to elucidate the response of hepatic microcirculation to endotoxin 2 weeks after bile duct ligation (BDL) or sham-operation in rats. Two hours after lipopolysaccharide (LPS) injection (1, 10, or 100 microg/kg, iv.), the hepatic microvasculature was examined using in vivo microscopy. BDL elicited increases in leukocytes adhering to the sinusoidal wall, swelling of sinusoidal endothelial cells as well as phagocytic activity of hepatic macrophages and a decrease in the numbers of perfused sinusoids. LPS (1, 10, 100 microg/kg) further increased leukocyte adhesion and reduced the numbers of perfused sinusoids in a dose-dependent manner. Leukocyte adhesion in response to LPS (1, 10, 100 microg/kg) in BDL rats was increased 6.1-fold, 5.9-fold, and 3.3-fold, respectively when compared with sham-operated rats. The numbers of perfused sinusoids in response to LPS (1, 10, 100 microg/kg) in BDL rats were decreased by 42%, 36%, and 45%. While 1 and 10 microg/kg LPS also elicited an increase in phagocytic activity in BDL rats when compared with sham-operated rats, the response to 100 microg/kg LPS was suppressed. LPS did not affect the numbers of swollen endothelial cell in BDL rats. The present study demonstrated that chronic biliary obstruction enhanced the hepatic microvascular response to low doses of endotoxin. This observation suggests that exaggerated hepatic microcirculatory dysfunction during sepsis contributes to the development of liver injury and a high incidence of morbidity and mortality in biliary obstruction.

Portosystemic shunting and persistent fetal vascular structures in aryl hydrocarbon receptor-deficient mice.

A physiological examination of mice harboring a null allele at the aryl hydrocarbon (Ah) locus revealed that the encoded aryl hydrocarbon receptor plays a role in the resolution of fetal vascular structures during development. Although the aryl hydrocarbon receptor is more commonly studied for its role in regulating xenobiotic metabolism and dioxin toxicity, a developmental role of this protein is supported by the observation that Ah null mice display smaller livers, reduced fecundity, and decreased body weights. Upon investigating the liver phenotype, we found that the decrease in liver size is directly related to a reduction in hepatocyte size. We also found that smaller hepatocyte size is the result of massive portosystemic shunting in null animals. Colloidal carbon uptake and microsphere perfusion studies indicated that 56% of portal blood flow bypasses the liver sinusoids. Latex corrosion casts and angiography demonstrated that shunting is consistent with the existence of a patent ductus venosus in adult animals. Importantly, fetal vascular structures were also observed at other sites. Intravital microscopy demonstrated an immature sinusoidal architecture in the liver and persistent hyaloid arteries in the eyes of adult Ah null mice, whereas corrosion casting experiments described aberrations in kidney vascular patterns.

Blood interleukin-6 and tumor necrosis factor-alpha elevation after intracerebroventricular injection of Escherichia coli endotoxin in the rat is determined by two opposing factors: peripheral induction by LPS transferred from brain to blood and inhibition of peripheral response by a brain-mediated mechanism.

Following intracerebroventricular injection of LPS in rats, IL-6 and TNF-alpha appear in peripheral blood. To determine whether these changes are mediated by passage of the injected LPS from the brain to the blood, the time course of appearance in blood of bioactive LPS after intracerebroventricular injection was compared with the time course of appearance of IL-6 and of TNF-alpha in blood. Bioactive LPS was detected 30 min after intracerebroventricular injection, the first time interval tested. TNF-alpha appeared in peripheral blood at 30 min, IL-6 at 60 min and both cytokines as well as LPS achieved highest levels at 120 min. To determine pharmacokinetics of LPS transfer from brain to blood more precisely, radioiodinated LPS was injected intracerebroventricularly. (125)I-LPS was detected in blood as early as 5 min after intracerebroventricular injection, reached peak levels at about 2 h, and was transferred from brain to blood at a rate corresponding to bulk flow (% of brain content per min was 1.40 +/- 0.58 and 1.00 +/- 0.21% in series 1 and 2, respectively). 70.0% of total injected LPS had entered blood by 4 h. However, when administered intravenously (by a programmed pump) at the same rate that it enters the blood after intracerebroventricular injection LPS induced a much greater cytokine response than when given intracerebroventricularly. This paradoxical response was shown in further studies to be due to the simultaneous central inhibitory effect of LPS; coinjection of intracerebroventricular LPS markedly reduced the peripheral cytokine response to intravenous LPS infusion.

Artificial formula induces precocious maturation of the small intestine of artificially reared suckling rats.

BACKGROUND: The artificially reared rat model was used successfully to study the effect of nutrition during the early postnatal period on growth and development of the neonate. Overgrowth and morphologic changes of the gastrointestinal tract are known consequences of artificial rearing. The major goal of our study was to elucidate whether artificial rearing-enhanced gut development is caused by artificial diet or by gastrostomy and the artificial rearing technique itself. METHODS: Suckling rats at day 8 of age underwent intragastric cannulation and were machine fed either a cow's milk-based artificial rat's milk substitute or pooled rat's milk for 4 days. Dam-fed littermates served as a control. RESULTS: Body growth did not differ in the three experimental groups. In rats receiving rat's milk substitute, small intestinal wet weight was approximately 60% greater than in rats fed rat's milk or control rats. Additionally, the entire small intestine was approximately 20% longer in the rat's milk substitute group. Morphologically, rat's milk substitute-fed pups demonstrated significantly greater intestinal villus length and crypt depth compared with rat's milk-fed or control rats. Jejunum and midjejunum of the rat's milk and control groups did not differ in these parameters. Intestinal sucrase activity of rat's milk substitute-fed rats was significantly elevated compared with rat's milk-fed rats or control animals. CONCLUSIONS: These results indicate that cow's milk-based formula, not gastrostomy or artificial feeding technique, is a principal cause of the small intestine overgrowth and precocious maturation of some intestinal functions observed in artificially reared sucklings.

High doses of intravenous immunoglobulin G enhance Kupffer cell phagocytic function during the late phase of sepsis and endotoxemia in rats.

The effect of intravenous immunoglobuln G (ivIG) on the hepatic microvascular inflammatory response during the late phase of sepsis and endotoxemia in rats was studied by using in vivo microscopy. One hour after administration of a clinically relevant dose of ivIG (0.5 g/kg body weight, Sandoglobulin), rats were subjected to polymicrobial sepsis induced by cecal ligation and puncture (CLP) or were injected intravenously with lipopolysaccharide (LPS, 0.1 mg/kg body weight). Twenty-four hours after CLP or LPS, the number of leukocytes adhering to the sinusoidal wall was increased 11.0-fold in CLP-treated animals and 5.6-fold in LPS-treated animals, respectively, compared with the controls. Concomitantly, the numbers of swollen sinusoidal endothelial cells were increased 4.2-fold and 3.2-fold. The number of perfused sinusoids was decreased by 35% and by 24%. These responses were minimized by pretreatment with high doses of ivIG. Kupffer cell phagocytic activity in the periportal sinusoids in CLP-treated animals was decreased by 41%, whereas that in the centrilobular sinusoids in LPS-treated animals was increased by 72%. IvIG significantly elevated this activity in both CLP- and LPS-treated animals and the number of ED2-positive Kupffer cells in tissue sections. The results suggest that ivIG limits the hepatic microvascular inflammatory response during the late phase of sepsis and endotoxemia by affecting Kupffer cell function.

Morphological mechanisms for regulating blood flow through hepatic sinusoids.

This review summarizes what is known about the various morphological sites that regulate the distribution of blood flow to and from the sinusoids in the hepatic microvascular system. These sites potentially include the various segments of the afferent portal venules and hepatic arterioles, the sinusoids themselves, and central and hepatic venules. Given the paucity of smooth muscle in the walls of these vessels, various sinusoidal lining cells have been suggested to play a role in regulating the diameters of sinusoids and influencing the distribution and velocity of blood flow in these vessels. While sinusoidal endothelial cells have been demonstrated to be contractile and to exhibit sphincter function, attention has recently focused on the perisinusoidal stellate cell as the cell responsible for controlling the sinusoidal diameter. A very recent study, however, suggested that the principal site of vasoconstriction elicited by ET-1 was the pre-terminal portal venule. This raised the question of whether or not the diameters of sinusoids might decrease due to passive recoil when inflow is reduced or eliminated and intra-sinusoidal pressure falls. In more recent in vivo microscopic studies, clamping of the portal vein dramatically reduced sinusoidal blood flow as well as the diameters of sinusoids. The sinusoidal lumens rapidly returned to their initial diameters upon restoration of portal blood flow suggesting that sinusoidal blood pressure normally distends the sinusoidal wall which can recoil when the pressure drops. Stellate cells may be responsible for this reaction given the nature of their attachment to parenchymal cells by obliquely oriented microprojections from the lateral edges of their subendothelial processes. This suggests that care must be exercised when interpreting the mechanism for the reduction of sinusoidal diameters following drug administration without knowledge of changes occurring to the portal venous and hepatic inflow.

Milk-borne epidermal growth factor modulates intestinal transforming growth factor-alpha levels in neonatal rats.

Epidermal growth factor (EGF) is present in milk from various mammalian species, but its physiologic function in neonatal development remains unclear. Transforming growth factor-alpha (TGF-alpha) is a peptide structurally related to EGF, and its presence is detected in the developing small intestine of rats. The purpose of the present study was to examine the effect of milk-borne EGF on endogenous production of EGF and TGF-alpha in the small intestine of suckling rats. Neonatal rats were fed via gastrostomy either growth factor-free rat milk substitute (RMS) or RMS supplemented with EGF (100 ng/mL of RMS) from 8 to 12 d of age. Artificially reared rats were then compared with their dam-fed littermates. Animals fed the EGF-deficient diet RMS had markedly increased EGF and TGF-alpha mRNA levels in duodenum and ileum compared with dam-fed controls and significantly elevated total intestinal content of TGF-alpha peptide. Intestinal EGF content and EGF serum levels were significantly decreased in the RMS group compared with controls. The addition of EGF to the RMS diet normalized TGF-alpha mRNA levels in the duodenum and ileum, EGF mRNA levels in the ileum, and total intestinal TGF-alpha content and EGF serum levels to the levels measured in dam-fed littermates. Motility studies showed that enteral administration of EGF did not affect stomach emptying and intestinal transit. These studies indicate that exogenous milk-borne EGF modulates endogenous production of TGF-alpha in developing small intestine. It is likely that neither TGF-alpha nor EGF are solely responsible for small intestinal overgrowth of artificially reared neonatal rats.

Characterization of a reproducible rat model of hepatic veno-occlusive disease.

Lack of a reproducible animal model has hampered progress in understanding hepatic veno-occlusive disease (HVOD). This article characterizes a reproducible model of HVOD. Rats gavaged with monocrotaline, 160 mg/kg, were killed between days 1 and 10. Sections were evaluated by light microscopy with a standardized scoring system, by immunoperoxidase staining with ED-1 (monocytes, macrophages) and ED-2 (Kupffer cells) antibodies, and by transmission (TEM) and scanning electron microscopy (SEM). On days 1 and 2, the earliest manifestations were progressive injury to the sinusoidal wall with loss of sinusoidal lining cells, sinusoidal hemorrhage, and mild damage to central vein (CV) endothelium. On days 3 through 5 ("early HVOD"), there was centrilobular coagulative necrosis, severe injury to sinusoids, severe sinusoidal hemorrhage, and severe CV endothelial damage; inflammation with ED-1-positive cells was most marked on these days. Days 6 and 7 ("late HVOD") were characterized by subendothelial and advential fibrosis of CVs, damage of the CV endothelium with subendothelial hemorrhage, and some restoration of the sinusoidal wall. Between days 8 and 10, sections showed interindividual variation ranging from mild, residual fibrosis to severe, late HVOD. From days 1 through 10, ED-2-positive cells were decreased in number, and the number of ED-1-positive cells was increased. Sinusoidal damage is the earliest change in HVOD. Coagulative necrosis follows sinusoidal injury and resolves with improvement in sinusoidal endothelial cell (SEC) morphology. Moderate-to-severe CV fibrosis occurs after reappearance of sinusoidal lining cells and resolution of hepatocyte necrosis. The inflammatory response within the lobule and CVs is a result of recruitment of monocytes, whereas Kupffer cells are decreased in number.

Effect of intravenous immunoglobulin G on the TNFalpha-mediated hepatic microvascular inflammatory response.

The effect of intravenous immunoglobulin G (ivIG) on the hepatic microvascular inflammatory response elicited by tumor necrosis factor alpha (TNFalpha) in rats was studied by means of in vivo microscopy and histological examination. One hour after the portal infusion of TNFalpha, the average number of leukocytes adhering to the sinusoidal endothelium was increased sevenfold, and the average number of the perfused sinusoids was decreased by 15% when compared with controls. Concomitantly, the expression of intercellular adhesion molecule-1 (ICAM-1) on the hepatic sinusoidal endothelium and that of the central vein was increased. The phagocytic activity of Kupffer cells in centrilobular sinusoids was increased by 54%, as were the number of ED2-positive Kupffer cells in tissue sections. Pretreatment with a clinically relevant high dose of ivIG (1 g/kg body weight, Sandoglobulin) minimized these responses by reducing leukocyte-endothelial interactions and Kupffer cell phagocytic function. The results suggest that high doses of ivIG limit the hepatic microvascular inflammatory response by inhibiting the action of the proinflammatory cytokine TNFalpha.

In vivo and electron microscopic observations of the responses of the hepatic sinusoid to interleukin-1.

Interleukin-1 (IL-1), which is produced by Kupffer cells and sinusoidal endothelial cells, may play an important role in immunological and microvascular responses to a variety of stimuli in the liver. The responses of the hepatic microvasculature including phagocytic activity of sinusoidal lining cells to IL-1 alpha were examined in C57Bl/6 mice in vivo and using electron microscopy. One hour after recombinant mouse IL-1 alpha was injected at doses of 80 U, the low dose group, and 800 U, the high dose group, the phagocytic activity of sinusoidal lining cells showed significant differences between the two treated groups and between the two groups and the controls. In the low dose group, the numbers of sinusoids containing blood flow and of leukocytes adhering to the sinusoidal lining remained unchanged, but the former decreased and the latter increased significantly in the high dose group. Ultrastructurally, Kupffer cells that phagocytosed latex particles appeared to have decreased in number while the sinusoidal endothelial cells became phagocytic. A considerable number of leukocytes were seen adhering to the sinusoidal endothelium. These findings demonstrate that IL-1 alpha not only elicited sticking and plugging by leukocytes in sinusoids but also activated phagocytic functions in the hepatic sinusoidal endothelial cells. These endothelial responses are similar to those seen following FV3 virus infection, chronic administration of ethanol, or a combination of cocaine and ethanol, or during extracorporal perfusion, suggesting that IL-1 may participate in these responses.

Glutathione protects metastatic melanoma cells against oxidative stress in the murine hepatic microvasculature.

Calcein-labeled B16 melanoma (B16M) cells were injected intraportally, and in vivo video microscopy was used to study the distribution and damage of cancer cells arrested in the liver microvasculature over a period of 4 hours. The contribution of glutathione (GSH)-dependent antioxidant machinery to the possible oxidative stress-resistance mechanism of B16M cell was determined by in vitro incubation with the selective inhibitor of GSH synthesis L-buthionine (S,R)-sulphoximine (BSO) before B16M cell injection in untreated and 0.5-mg/kg lipopolysaccharide (LPS)-treated mice. In addition, untreated and LPS-treated isolated syngeneic hepatic sinusoidal endothelial cells (HSE) were used to determine in vitro their specific contribution to B16M cell damage. Trauma inherent to intrasinusoidal lodgement damaged 35% of B16M cells in both normal and LPS-treated mouse liver. The rest of the arrested B16M cells remained intact in normal liver for at least 4 hours, although their damaged cell percentage significantly (P < .05) increased since the second hour in normal mice injected with BSO-treated cells and since the first hour in LPS-treated mice given untreated cells. Recombinant human interleukin-1 receptor antagonist (rHuIL-1-Ra) given to mice 15 minutes before LPS significantly (P < .05) abrogated B16M cell damage. On the other hand, 40% of the B16M cells co-cultured with unstimulated HSE and 70% of the co-cultured with LPS-treated HSE became sensitive to endothelial cell-mediated damage after BSO treatment. These results demonstrate that a high intracellular level of GSH protects B16M cells from possible in vivo and in vitro sinusoidal cell-mediated oxidative stress, contributing to the mechanism of metastatic cell survival within the hepatic microvasculature.

Sphincters of canine hepatic sublobular veins respond to endothelin-1 and 3.

The dog has been used repeatedly as a model in liver transplantation research. The microcirculation and its regulatory mechanisms play a crucial role during ischemia and reperfusion. Little is known about the role of venous sphincters in regulating blood flow in the dog liver. Hence, we performed this study to elucidate their potential role in regulating local blood flow. In 14 dogs mean systemic (MSP) and mean portal venous pressure (MPP) were measured. Light and electron microscopy (scanning and transmission) of tissue sections and vascular corrosion casts were used to elucidate the microvascular morphology. Immunocytochemistry was applied to identify smooth muscle cells and the innervation of venous sphincters. Endothelins 1 and 3 were injected to find whether the hepatic venous sphincters are sensitive to these vasoactive agents. Tufts of smooth muscle cells were found in the sublobular veins (SLV; 100 to 250 microm in diameter), that reduced the luminal diameters of veins by 34%. Nerve endings were not observed close to these venous sphincters. The MSP and MPP were 75.3+/-2.4 mmHg and 8.9+/-0.95 mmHg, respectively. Treatment with 1.0 microg/kg of endothelin-1 (ET-1) significantly increased the MSP, the MPP and the percentage of focal venous sphincter contraction by 39% (105+/-4.7 mmHg), 43% (12.8+/-1.7 mmHg) and 57% (53.5+/-4.7), respectively (P <0.01). Treatment with ET-3 caused a significant (P <0.01) decrease in the MSP, the MPP and the percentage of sphincter contraction by 19% (61.0+/-2.2 mmHg), 39% (5.8+/-2.9 mmHg) and 38% (20.9%+/-3.15). Sinusoids did not contain sphincters. Hepatic arterioles and central veins were not affected by ET-treatment. The contraction of SLV sphincters correlated with increases in MPP (r=0.81, P <0.01) and was related to the MSP (r=0.67, P <0.01). These data show that the smooth muscle sphincters in SLV of the dog liver are involved in the local regulation of blood flow and that these sphincters are stimulated by non-neurogenic mechanisms. These sphincters contract in response to ET-1 and relax in response to ET-3. Since ET-1 is released during and/or causes inflammation, e.g., during ischemia and reperfusion, its antagonists might be of benefit during transplantation reperfusion of liver.

In vivo microscopy of the exocrine pancreas.

Light microscopic studies of the living acinar pancreas, although limited in number, have revealed valuable information concerning dynamic aspects of microvascular and parenchymal structure and function. For example, it has been found that: 1) the living organ in anesthetized animals can be imaged with a resolution approaching the limit of the light microscope; 2) blood flow through individual capillaries in the exocrine pancreas is intermittent; 3) blood flow through these capillaries is regulated locally by smooth muscle precapillary sphincters and within individual capillaries by endothelial cells which are spontaneously contractile as well as responsive to vasoactive substances; and 4) the formation and release of zymogen granules occurs within 45-90 minutes in acinar cells stimulated with pancreozymin. This paper reviews these studies and some of the methods used to obtain them.

Modulation of Kupffer cell and peripheral blood monocyte activity by in vivo treatment of rats with all-trans-retinol.

Previous studies have shown that large doses of vitamin A potentiate chemical-induced liver injury and that the Kupffer cell is directly involved in this potentiation. Therefore, these studies were designed to determine if Kupffer cells isolated from vitamin A treated male Sprague-Dawley rats (75 mg/kg/day for 3-7 days as all- trans-retinol) had altered activity and function. Respiratory activity of Kupffer cells isolated from rats treated with vitamin A for 3 to 7 days markedly increased. Similarly, phagocytic activity was significantly elevated (up to 9-fold) after exposure to vitamin A for 3 to 7 days. Production of reactive oxygen species, measured by luminol-enhanced chemiluminescence of Kupffer cells isolated after 7 days of vitamin A exposure, was significantly higher than that of control cells when stimulated with opsonized zymosan. Also, the release of superoxide anion by individual Kupffer cells isolated from vitamin A treated rats was nearly three times greater than that of control cells. Basal production of tumor necrosis factor-alpha (TNF-alpha) and prostaglandin E2 (PGE2) production were significantly elevated in Kupffer cells isolated from rats treated with vitamin A. Lastly, peripheral blood monocytes (PBMC) isolated from rats treated with vitamin A for 7 days had a significantly greater respiratory activity, as well as TNF-alpha and PGE2 production, than PBMC isolated from control rats. Our data suggest that large doses of vitamin A enhance both Kupffer cell and PBMC function. Upregulation of the activity by these phagocytic cells may play a role in the vitamin A potentiation of chemical-induced liver injury.