Hormonal control of glycogenolysis in parenchymal liver cells by Kupffer and endothelial liver cells

Intercellular crosstalk of liver sinusoidal endothelial cells in liver fibrosis, cirrhosis and hepatocellular carcinoma

Intercellular crosstalk among various liver cells plays an important role in liver fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). Capillarization of liver sinusoidal endothelial cells (LSECs) precedes fibrosis and accumulating evidence suggests that the crosstalk between LSECs and other liver cells is critical in the development and progression of liver fibrosis. LSECs dysfunction, a key event in the progression from fibrosis to cirrhosis, and subsequently obstruction of hepatic sinuses and increased intrahepatic vascular resistance (IHVR) contribute to development of portal hypertension (PHT) and cirrhosis. More importantly, immunosuppressive tumor microenvironment (TME), which is closely related to the crosstalk between LSECs and immune liver cells like CD8+ T cells, promotes advances tumorigenesis, especially HCC. However, the connections within the crosstalk between LSECs and other liver cells during the progression from liver fibrosis to cirrhosis to HCC have yet to be discussed. In this review, we first summarize the current knowledge of how different crosstalk between LSECs and other liver cells, including hepatocytes, hepatic stellate cells (HSCs), macrophoges, immune cells in liver and extra cellular matrix (ECM) contribute to the physiological function and the progrssion from liver fibrosis to cirrhosis, or even to HCC. Then we examine current treatment strategies for LSECs crosstalk in liver fibrosis, cirrhosis and HCC.

Early-Phase Alcoholic Liver Disease: An Update on Animal Models, Pathology, and Pathogenesis

Alcoholic liver disease (ALD) remains to be one of the most common etiology of liver disease and is a major cause of morbidity and mortality worldwide. The pathologic stages of ALD comprises of steatosis, steatohepatitis, and fibrosis/cirrhosis. Steatosis and steatohepatitis represents the early phase of ALD and are precursor stages for fibrosis/cirrhosis. Numerous research efforts have been directed at recognizing cofactors interacting with alcohol in the pathogenesis of steatosis and steatohepatitis. This review will elucidate the constellation of complex pathogenesis, available animal models, and microscopic pathologic findings mostly in the early-phase of ALD. The role of endotoxin, reactive oxygen species, alcohol metabolism, and cytokines are discussed. Understanding the mechanisms of early-phase ALD should provide insight into the development of therapeutic strategies and thereby decrease the morbidity and mortality associated with ALD.

Liver sinusoidal endothelial cells link hyperinsulinemia to hepatic insulin resistance

Insulin signaling in vascular endothelial cells (ECs) is critical to maintain endothelial function but also to mediate insulin action on peripheral glucose disposal. However, gene knockout studies have reached disparate conclusions. Thus, insulin receptor inactivation in ECs does not impair insulin action, whereas inactivation of Irs2 does. Previously, we have shown that endothelial ablation of the three Foxo genes protects mice from atherosclerosis. Interestingly, here we show that mice lacking FoxO isoforms in ECs develop hepatic insulin resistance through excessive generation of nitric oxide (NO) that impairs insulin action in hepatocytes via tyrosine nitration of insulin receptors. Coculture experiments demonstrate that NO produced in liver sinusoidal ECs impairs insulin's ability to suppress glucose production in hepatocytes. The effects of liver sinusoidal ECs can be mimicked by NO donors and can be reversed by NO inhibitors in vivo and ex vivo. The findings are consistent with a model in which excessive, rather than reduced, insulin signaling in ECs predisposes to systemic insulin resistance, prompting a reevaluation of current approaches to insulin sensitization.

[Carbohydrate metabolism dysregulation in cirrhosis: pathophysiology, prognostic impact and therapeutic implications]

The liver plays a key-role in carbohydrates metabolism. Glucose intole-rance, overt diabetes mellitus and insulin resistance are characteristic features of patients with cirrhosis. Central hyperinsulinemia and peripheral insulin-resistance are the main explanations for the high prevalence of diabetes in patients with cirrhosis. On the other hand, type 2 diabetes is associated with a wide spectrum of liver diseases ranging from nonalcoholic fatty liver to cirrhosis and hepatocellular carcinoma. Carbohydrate metabolism abnormalities are a major aggravating risk factor in cirrhosis. Diabetes is also an independent negative prognostic factor in cirrhotic patients. This leads to specific diagnostic procedures and therapeutic issues. Patients with diabetes and liver disease frequently need insulin treatment. The presence of liver disease makes the treatment of diabetes complex, and additional research is needed to determine the best treatment strategies in these patients.

Macrophage PPAR gamma is required for normal skeletal muscle and hepatic insulin sensitivity and full antidiabetic effects of thiazolidinediones

PPAR gamma is required for fat cell development and is the molecular target of antidiabetic thiazolidinediones (TZDs), which exert insulin-sensitizing effects in adipose tissue, skeletal muscle, and liver. Unexpectedly, we found that inactivation of PPAR gamma in macrophages results in the development of significant glucose intolerance plus skeletal muscle and hepatic insulin resistance in lean mice fed a normal diet. This phenotype was associated with increased expression of inflammatory markers and impaired insulin signaling in adipose tissue, muscle, and liver. PPAR gamma-deficient macrophages secreted elevated levels of factors that impair insulin responsiveness in muscle cells in a manner that was enhanced by exposure to FFAs. Consistent with this, the relative degree of insulin resistance became more severe in mice lacking macrophage PPAR gamma following high-fat feeding, and these mice were only partially responsive to TZD treatment. These findings reveal an essential role of PPAR gamma in macrophages for the maintenance of whole-body insulin action and in mediating the antidiabetic actions of TZDs.

Diabetes in chronic liver disease: from old concepts to new evidence

The liver is one of the principal organs involved in glucose metabolism together with skeletal muscle and adipose tissue. A link between diabetes and chronic liver disease (CLD) was first observed in the early half of the last century, but to date several questions remain unsolved. Altered glucose tolerance has been well described in alcoholic CLD, non-alcoholic fatty liver disease, chronic hepatitis C and portal hypertension. Moreover, insulin resistance is assuming an ever-growing importance in CLD; chronic hepatitis C has recently been proposed as a metabolic disease and insulin sensitivity as a predictive factor for liver fibrosis.CLD is also complicated by acquired growth hormone (GH) resistance, characterized by low concentrations of insulin-like growth factor-1 (IGF-1) with respect to normal or elevated GH levels. GH resistance in CLD is determined by several factors, including malnutrition, impaired liver function and reduced expression of hepatic GH receptors. We recently described the possible role of tumour necrosis factor-alpha (TNF-alpha) in blunting the hepatic response to GH in patients with chronic hepatitis C. The role of GH in impaired glucose metabolism is well known, and recent evidence suggests a receptor and/or post-receptor modulation of insulin signalling. Moreover, as in other chronic inflammatory conditions, pro-inflammatory cytokines may directly modulate the signal cascade that follows insulin binding to its receptor in the course of CLD. In this review, the proposed links between impaired glucose tolerance and CLD are analysed, special emphasis being focussed on the most recent findings concerning the interplay of chronic inflammation, GH resistance and insulin resistance.

Involvement of cyclooxygenase-2 in the potentiation of allyl alcohol-induced liver injury by bacterial lipopolysaccharide

Bacterial endotoxin (lipopolysaccharide; LPS) augments the hepatotoxicity of a number of xenobiotics including allyl alcohol. The mechanism for this effect is known to involve the inflammatory response elicited by LPS. Upregulation of cyclooxygenase-2 (COX-2) and production of eicosanoids are important aspects of inflammation, therefore studies were undertaken to investigate the role of COX-2 in LPS-induced enhancement of liver injury from allyl alcohol. Rats were pretreated (iv) with a noninjurious dose of LPS or sterile saline vehicle and 2 h later were treated (ip) with a noninjurious dose of allyl alcohol or saline vehicle. COX-2 mRNA was determined by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR), and liver injury was assessed from activities in serum of alanine and aspartate aminotransferases (ALT and AST, respectively) and from histology. Liver injury was observed only in rats cotreated with LPS and allyl alcohol. Serum ALT activity was increased by 4 h after administration of LPS and continued to increase through 8 h. COX-2 mRNA was detectable at low levels in livers from rats receiving only the vehicles at any time up to 8 h. Expression of COX-2 mRNA was increased by 30 min after administration of LPS and remained elevated through 6 h. Allyl alcohol treatment alone caused an increase in COX-2 mRNA at 4 h (2 h after allyl alcohol) that lasted less than 2 h. In livers from rats cotreated with LPS and allyl alcohol, levels of COX-2 mRNA were greater than levels seen with either LPS or allyl alcohol alone. The increased expression of COX-2 mRNA was accompanied by an increase in the concentration of prostaglandin (PG) D(2) in plasma. Plasma PGD(2) concentration was increased to a greater extent in rats treated with LPS plus allyl alcohol compared to allyl alcohol or LPS alone. Pretreatment with the COX-2 selective inhibitor, NS-398, abolished the increase in plasma PGD(2) and reduced the increase in ALT and AST activities observed in rats cotreated with LPS and allyl alcohol. NS-398 did not affect liver injury from allyl alcohol alone administered at a larger, hepatotoxic dose. In addition, ibuprofen, a nonselective inhibitor of cyclooxygenases, did not protect against liver injury from LPS plus allyl alcohol. In isolated hepatocytes PGD(2), but not PGE(2), reduced the concentration of allyl alcohol required to cause half-maximal cytotoxicity. These results suggest that products of COX-2 play a role in the augmentation of allyl alcohol-induced liver injury by LPS.

Induction by interleukin 6 of G(s)-coupled prostaglandin E(2) receptors in rat hepatocytes mediating a prostaglandin E(2)-dependent inhibition of the hepatocyte's acute phase response

Prostanoids, that are released from nonparenchymal liver cells in response to proinflammatory stimuli, are involved in the regulation of hepatic functions during inflammation. They exert their effects on their target cells via heptahelical receptors in the plasma membrane. For the 5 prostanoids prostaglandin E(2) (PGE(2)), prostaglandin F(2alpha), prostaglandin D(2) (PGD(2)), prostacyclin, and thromboxane A(2) there exist 8 receptors that are coupled to different heterotrimeric G proteins. These receptors are expressed differentially in the 4 principal liver cell types, i.e., hepatocytes, Kupffer cells, sinusoidal endothelial cells, and hepatic stellate cells. It was intriguing, that the messenger RNA (mRNA) of none of the G(s)-coupled prostanoid receptors (DP-R, EP2-R, EP4-R, and IP-R) that can attenuate the inflammatory reaction were present in hepatocytes. The current study shows that the expression of the G(s)-coupled prostanoid receptors EP2-R, EP4-R, and DP-R, but not the IP-R, was efficiently and rapidly up-regulated by treatment of hepatocytes in vitro or rats in vivo with the key acute phase cytokine interleukin 6 (IL-6). In IL-6-treated hepatocytes PGE(2) in turn attenuated the IL-6-induced alpha(2)-macroglobulin formation via a cyclic adenosine monophosphate (cAMP)-dependent signal chain. The data indicate that an IL-6-mediated induction of the previously not expressed EP2-R and EP4-R on hepatocytes might establish a prostanoid-mediated feedback inhibition loop for the attenuation of the acute phase response.

Role of endotoxin in the hypermetabolic state after acute ethanol exposure

This study investigated the role of endotoxin in the hypermetabolic state or swift increase in alcohol metabolism (SIAM) due to acute ethanol exposure. Female Sprague-Dawley rats (100-120 g) were given ethanol (5 g/kg) by gavage. Endotoxin measured in plasma from portal blood was not detectable in saline-treated controls; however, 90 min after ethanol, endotoxin was increased to 85 +/- 14 pg/ml, and endotoxin clearance was diminished by approximately 50%. Oxygen uptake in perfused livers was increased 48% by ethanol, and production of PGE2 by isolated Kupffer cells was increased similarly. These effects were blunted by elimination of gram-negative bacteria and endotoxin with antibiotics before ethanol administration. To reproduce ethanol-induced endotoxemia, endotoxin was infused via the mesenteric vein at a rate of 2 ng. kg-1. h-1. Endotoxin mimicked the effect of ethanol on oxygen uptake. The specific Kupffer cell toxicant GdCl3 completely prevented increases in oxygen uptake due to endotoxin. These findings demonstrate that endotoxin plays a pivotal role in SIAM, most likely by stimulating eicosanoid release from Kupffer cells.

Cyclooxygenase inhibition potentiates the renal vascular response to endothelin-1 in humans

Vascular endothelin-receptor stimulation results in vasoconstriction and concomitant production of the vasodilators prostaglandin I2 and nitric oxide. The vascular effects of cyclooxygenase (COx) blockade (diclofenac intravenously) and the subsequent vasoconstrictor response to endothelin-1 (ET-1) infusion 30 min after diclofenac were studied in healthy men. With COx blockade, cardiac output (7%) and splanchnic (14%) and renal (12%) blood flows fell (all P < 0.001). Splanchnic blood flow returned to basal value within 30 min. Mean arterial blood pressure increased (4%, P < 0.001). Splanchnic glucose output fell (22%, P < 0.01). Subsequent ET-1 infusion caused, compared with previous ET-1 infusion without COx blockade (G. Ahlborg, E. Weitzberg, and J. M. Lundberg. J. Appl. Physiol. 77: 121-126, 1994; E. Weitzberg, G. Ahlborg, and J. M. Lundberg. Biochem. Biophys. Res. Commun. 180: 1298-1303, 1991; E. Weitzberg, G. Ahlborg, and J. M. Lundberg. Clin. Physiol. (Colch.) 13: 653-662, 1993), the same increase in mean arterial blood pressure (4%), decreases in cardiac output (13%) and splanchnic blood flow (38%), but no significant change in splanchnic glucose output. Renal blood flow reduction was potentiated (33 +/- 3 vs. 23 +/- 2%, P < 0.02), with a total reduction corresponding to 43 +/- 3% (P < 0.01 vs. 23 +/- 3%). We conclude that COx inhibition induces renal and splanchnic vasoconstriction. The selectively increased renal vascular responsiveness to ET-1 emphasizes the importance of endogenous arachidonic acid metabolites (i.e., prostaglandin I2) to counteract ET-1-mediated renal vasoconstriction.

II. Alcoholic liver injury involves activation of Kupffer cells by endotoxin

It is well known that females show a greater susceptibility to alcohol-induced liver injury than males. Additionally, females who consume alcohol regularly and have been obese for 10 years or more are at greater risk for both hepatitis and cirrhosis. Female rats on an enteral alcohol protocol exhibit injury more quickly than males, with widespread fatty changes over a larger portion of the liver lobule. Levels of plasma endotoxin, intercellular adhesion molecule-1, free radical adducts, infiltrating neutrophils, and nuclear factor-kappaB are increased about twofold more in livers from female than male rats after enteral alcohol treatment. Estrogen treatment in vivo increases the sensitivity of Kupffer cells to endotoxin. Evidence has been presented that Kupffer cells are pivotal in the development of alcohol-induced liver injury. Destruction of Kupffer cells with gadolinium chloride (GdCl3) or reduction of bacterial endotoxin by sterilization of the gut with antibiotics blocks early inflammation due to alcohol. Similar results have been obtained with anti-tumor necrosis factor-alpha antibody. These findings led to the hypothesis that alcohol-induced liver injury involves increases in circulating endotoxin, leading to activation of Kupffer cells, which causes a hypoxia-reoxygenation injury. This idea has been tested using pimonidazole, a nitroimidazole marker, to quantitate hypoxia in downstream pericentral regions of the liver lobule. After chronic enteral alcohol, pimonidazole binding increases twofold. Enteral alcohol also increases free radicals detected with electron spin resonance. Importantly, hepatic hypoxia and radical production detected in bile are decreased by destruction of Kupffer cells with GdCl3. These data are consistent with the hypothesis that Kupffer cells participate in important gender differences in liver injury caused by alcohol.

Stimulation of oxygen uptake by prostaglandin E2 is oxygen dependent in perfused rat liver

The aim of this study was to determine if the effect of prostaglandin E2 (PGE2) on hepatic oxygen uptake was affected by oxygen tension. Livers from fed female Sprague-Dawley rats were perfused at normal or high flow rates (4 or 8 ml . g-1 . min-1) to vary local oxygen tension within the liver lobule. During perfusion at normal flow rates, PGE2 (5 microM) infusion increased oxygen uptake by about 50 micromol . g-1 . h-1; however, when livers were perfused at high flow rates, the increase was nearly twice as large. Simultaneously, glucose output was increased rapidly by about 50%, whereas glycolysis was decreased about 60%. When flow rate was held constant, increases in oxygen uptake due to PGE2 were proportional to oxygen delivery. Infusion of PGE2 into livers perfused at normal flow rates increased state 3 rates of oxygen uptake of subsequently isolated mitochondria by about 25%; however, rates were increased 50-75% in mitochondria isolated from livers perfused at high flow rates. Thus it is concluded that PGE2 stimulates oxygen uptake via mechanisms regulated by oxygen tension in perfused rat liver. High flow rates also increased basal rates of oxygen uptake: this increase was prevented by inactivation of Kupffer cells with GdCl3. In addition, conditioned medium from Kupffer cells incubated at high oxygen tension (75% oxygen) stimulated oxygen uptake of isolated parenchymal cells by >30% and elevated PGE2 production about twofold compared with Kupffer cells exposed to normal air-saturated buffer (21% oxygen). These effects were blocked completely by both indomethacin and nisoldipine. These data support the hypothesis that oxygen stimulates Kupffer cells to release mediators such as PGE2 which elevate oxygen consumption in parenchymal cells, possibly by mechanisms involving cyclooxygenase and calcium channels.

The role of gut-derived bacterial toxins and free radicals in alcohol-induced liver injury

Previous research from this laboratory using a continuous enteral ethanol (EtOH) administration model demonstrated that Kupffer cells are pivotal in the development of EtOH-induced liver injury. When Kupffer cells were destroyed using gadolinium chloride (GdCl₃ ) or the gut was sterilized with polymyxin B and neomycin, early inflammation due to EtOH was blocked. Anti-tumour necrosis factor (TNF)-α antibody markedly decreased EtOH-induced liver injury and increased TNF-mRNA. These findings led to the hypothesis that EtOH-induced liver injury involves increases in circulating endotoxin leading to activation of Kupffer cells. Pimonidazole, a nitro-imidazole marker, was used to detect hypoxia in downstream pericentral regions of the lobule. Following one large dose of EtOH or chronic enteral EtOH for 1 month, pimonidazole binding was increased significantly in pericentral regions of the liver lobule, which was diminished with GdCl₃ . Enteral EtOH increased free radical generation detected with electron spin resonance (ESR). These radical species had coupling constants matching α-hydroxyethyl radical and were shown conclusively to arise from EtOH based on a doubling of the ESR lines when ¹³ C-EtOH was given. α-Hydroxyethyl radical production was also blocked by the destruction of Kupffer cells with GdCl₃ . It is known that females develop more severe EtOH-induced liver injury more rapidly and with less EtOH than males. Female rats on the enteral protocol exhibited more rapid injury and more widespread fatty changes over a larger portion of the liver lobule than males. Plasma endotoxin, ICAM-1, free radical adducts, infiltrating neutrophils and transcription factor NFκB were approximately two-fold greater in livers from females than males after 4 weeks of enteral EtOH treatment. Furthermore, oestrogen treatment increased the sensitivity of Kupffer cells to endotoxin. These data are consistent with the hypothesis that Kupffer cells participate in important gender differences in liver injury caused by ethanol.

Primary role of Kupffer cell-hepatocyte communication in the expression of oxidative stress in the post-ischaemic liver

It has been reported that hepatocyte metabolism and function can be modulated by the activated Kupffer cell through the release of different biomolecules like cytokines, eicosanoids, oxygen free radicals and enzymes. In relation to these paracrine factors involved in circuits of intercellular communication, the existence of a hepatic oxygen sensor located in the Kupffer cell has been postulated. According to this postulate the oxygen metabolism of the liver parenchymal cells could be under the control of the Kupffer cells. In order to study the role of the Kupffer cell in the reperfusion syndrome of the liver, a lobular ischaemia-reperfusion model was performed in rats with or without previous treatment with gadolinium chloride to block Kupffer cell function. Spontaneous chemiluminescence of the liver surface, oxygen uptake by tissue slices and tertbutyl hydroperoxide-initiated chemiluminescence determinations were performed to evaluate the oxygen metabolism and the oxy-radical generation by the liver. The lower basal photoemission, in parallel with a lower basal oxygen uptake registered in the hepatic lobes from the animals pretreated with gadolinium chloride clearly indicates that the gadolinium chloride-dependent functional inhibition of Kupffer cell leads to a downregulation of oxygen metabolism by the liver. Moreover, the intensity of oxidative stress exhibited by the postischaemic lobes appears to be closely linked with the Kupffer cell activity. On the basis of the data obtained we propose that a paracrine circuit between activated Kupffer cell and hepatocytes is an early key event in the induction of postischaemic oxidative stress in the liver. Furthermore the interference with the mitochondrial electron flow by some biomolecules released from the activated Kupffer cell, such as tumour necrosis factor, interleukins, eicosanoids, etc., would increase the rate of generation of reactive oxygen species by the inhibited mitochondrial respiratory chain.

Indomethacin stimulates glucose production in adults with uncomplicated falciparum malaria

In healthy subjects, basal hepatic glucose production is (partly) regulated by paracrine intrahepatic factors. It is unknown if these paracrine factors also influence basal glucose production in infectious diseases with increased glucose production. We compared the effects of 150 mg indomethacin (n = 9), a nonendocrine stimulator of glucose production in healthy adults, and placebo (n = 7) on hepatic glucose production in Vietnamese adults with uncomplicated falciparum malaria. Glucose production was measured by primed, continuous infusion of [6,6-2H2]glucose. After indomethacin, the plasma glucose concentration and glucose production increased in all subjects from 5.3 +/- 0.1 mmol/L to a maximum of 7.1 +/- 0.3 mmol/L (P < .05) and from 17.6 +/- 0.8 micromol x kg(-1) x min(-1) to a maximum of 26.2 +/- 2.5 micromol x kg(-1) x min(-1) (P < .05), respectively. In the control group, the plasma glucose concentration and glucose production declined gradually during 4 hours from 5.4 +/- 0.2 mmol/L to 5.1 +/- 0.1 mmol/L (P < .05) and from 17.1 +/- 0.8 micromol x kg(-1) x min(-1) to 15.1 +/- 1.0 micromol x kg(-1) x min(-1) (P < .05), respectively. There were no differences in plasma concentrations of insulin, counterregulatory hormones, or cytokines between the groups. We conclude that indomethacin administration results in a transient increase in glucose production in patients with uncomplicated falciparum malaria in the absence of changes in plasma concentrations of glucoregulatory hormones or cytokines. Thus, this study indicates that in uncomplicated falciparum malaria, the rate of basal hepatic glucose production is also regulated by paracrine intrahepatic factors.

Plasma and metabolic abnormalities in Gaucher's disease

An overview of the most important plasma abnormalities that can be found in Gaucher's disease is presented in this chapter. Attention is focussed on their practical applications and possible clinical relevance. In addition, the result of studies on metabolic alterations in Gaucher's disease are reviewed.

Differential effects of enzyme supplementation therapy on manifestations of type 1 Gaucher disease

BACKGROUND

In type 1 Gaucher disease (GD), the accumulation of glucocerebroside in macrophages, caused by deficient activity of glucocerebrosidase, results in a variety of disease manifestations. In addition to the characteristic features of hepatosplenomegaly, cytopenia, and bone abnormalities, resting energy expenditure (REE) and glucose production are increased. In this study the effects of enzyme supplementation therapy on metabolic parameters in relation to other disease manifestations in type 1 GD patients are investigated.

PATIENTS AND METHODS

In 12 adult type 1 GD patients, measurements of REE (by indirect calorimetry), liver and spleen volume (by spiral computerized axial tomography [CT]) and hemoglobin and platelet count were obtained before and after 6 months of alglucerase therapy (15 U/kg per month). In 7 of the 12 patients hepatic glucose production was measured by infusing 3-3H glucose. For comparison, REE and glucose metabolism were studied in 7 weight- and age-matched healthy subjects.

RESULTS

REE and glucose production were increased in GD patients as compared with controls (REE: 29.8 kcal/kg/24 h +/- 3.6 and 23.1 +/- 2.3 kcal/kg/24 h, respectively, P < 0.05; glucose production: 14.00 mumol/kg/min +/- 0.51 and 10.77 mumol/kg/min +/- 0.26, respectively, P < 0.03). There were no differences in plasma glucose concentrations. Whereas the elevated REE decreased after 6 months of alglucerase therapy from 129% to 120% of predicted values (P < 0.01), the increase in hepatic glucose production did not change. An increase in weight occurred after 6 months of treatment (1.7 +/- 0.8 kg, P < 0.001), which was accounted for by an increase in fat mass of 1.6 +/- 1.5 kg (P < 0.02). Hemoglobin levels increased from 11.2 mg/dL to 12.1 mg/dL (P = 0.05) and platelet counts rose from 84 x 10(9)/L to 113 x 10(9)/L (P < 0.05). Although liver and spleen volumes decreased by approximately 10% and approximately 20%, respectively, there was no correlation between the decrease in organ volumes and the decrease in REE.

CONCLUSIONS

Treatment with alglucerase improves hypermetabolism and organomegaly in GD, whereas the increase in glucose production persists. Therefore, the dose-response effects of alglucerase are variable for the different manifestations of type 1 GD.

Lack of effect of calcitonin gene-related peptide and amylin on major markers of glucose metabolism in hepatocytes

Effects of amylin and calcitonin gene-related peptide on several processes involved in carbohydrate metabolism were investigated in rat hepatocytes, non-parenchymal cells (Kupffer, Ito and endothelial cells) and alveolar macrophages. In hepatocytes, cAMP levels were increased 25-fold by glucagon (10 nM), less than 2-fold by calcitonin gene-related peptide (100 nM) and not at all by amylin (100 nM). In non-parenchymal cells and cultured alveolar macrophages, calcitonin gene-related peptide potently, and amylin weakly, stimulated cAMP levels. In hepatocytes neither amylin nor calcitonin gene-related peptide affected glycogen phosphorylase activity, glucose output, lactate uptake, glycogen synthesis, glycogen mass or tyrosine aminotransferase activity. The density of calcitonin gene-related peptide specific binding sites in parenchymal cells was 10-fold less then seen in non-parenchymal cells. We found no significant evidence of specific amylin binding sites. These results are consistent with the notion that amylin does not exert a direct effect in hepatocytes. However, we do not rule out that amylin may affect hepatic glucose output indirectly through Cori cycling of lactate derived from skeletal muscle or from interactions through non-parenchymal cells.

Kupffer cell function in thyroid hormone-induced liver oxidative stress in the rat

The influence of thyroid hormone (L-3, 3', 5-triiodothyronine, T3) on Kupffer cell function was studied in the isolated perfused rat liver by colloidal carbon infusion. Rates of carbon uptake were determined from the influent minus effluent concentration difference and the flow rate, and the respective carbon-induced respiratory activity was calculated by integration of the area under the O2 curves during carbon infusion. In the concentration range of 0.2 to 2.0 mg of carbon/ml, livers from euthyroid rats exhibited a sigmoidal-type kinetics of carbon uptake, with a Vmax of 4.8 mg/g liver/min and a concentration of 0.82 mg/ml for half-maximal rate; carbon-induced O2 uptake presented a hyperbolic-type kinetics, with a Vmax of 4.57 mumol of O2/g liver and a K(m) of 0.74 mg of carbon/ml, which significantly correlates with the carbon uptake rates. Light-microscopy showed that carbon was taken up exclusively by non-parenchymal cells, predominantly by Kupffer cells. Thyroid calorigenesis was found in parallel with increased rates of hepatic O2 consumption and thiobarbituric acid reactive substances (TBARS) formation, glutathione (GSH) depletion, and higher sinusoidal lactate dehydrogenase (LDH) efflux compared to control values. In the concentration range of 0.25 to 0.75 mg/ml, carbon infusion did not modify liver LDH efflux in control rats, while it was significantly enhanced in T3-treated animals. In this latter group, higher carbon concentrations (1 and 1.3 mg/ml) led to loss of viability of the liver. At 0.25 to 0.75 mg of carbon/ml, both the rates of carbon uptake and the associated carbon-induced respiratory activities were significantly increased by T3 treatment, effects that were abolished by pretreatment of the rats with gadolinium chloride (GdCl3). In addition, GdCl3 decreased by 50% the changes induced by T3 in hepatic GSH content and TBARS formation. It is concluded that hyperthyroidism enhances Kupffer cell function, correlated with the increased number of liver macrophages observed histologically, which may represent an alternate source of reactive O2 species to that induced in parenchymal cells, thus contributing to the enhanced oxidative stress status developed.

Modulation of glucose production by indomethacin and pentoxifylline in healthy humans

Indomethacin, an inhibitor of prostaglandin synthesis that modulates cytokine production, increases hepatic glucose output (HGO) in humans. However, prostaglandins stimulate glucose production in vitro. To investigate the mechanism of HGO stimulation by indomethacin, we compared the effect of pentoxifylline, an inhibitor of cytokine production, versus saline (study 1, n = 6) and of indomethacin versus the combination of indomethacin and pentoxifylline (study 2, n = 5) on basal HGO. HGO was measured by primed, continuous infusion of 3-3H-glucose. In study 1, pentoxifylline infusion resulted in an immediate, transient decrease of HGO of approximately 50% (from 12.9 +/- 0.4 to 6.0 +/- 1.7 micromol/kg/min after 15 minutes, P < .03 v control). There were no differences in concentrations of glucoregulatory hormones between the two experiments. In study 2, after indomethacin administration, HGO increased transiently by approximately 84% (from 9.7 +/- 0.7 at baseline to 16.7 +/- 2.4 micromol/kg/min after 135 minutes, P < .05). However, pentoxifylline did not affect the increase in HGO induced by indomethacin. There were no differences in concentrations of glucoregulatory hormones between the two experiments. Therefore, indomethacin stimulates HGO by mechanisms unrelated to glucoregulatory hormones, prostaglandins, or cytokines.

Increase in histamine synthesis by liver macrophages in CCl4-injured mast cell-deficient W/Wv mice

This study set out to examine the possible role of liver macrophages in histamine synthesis in the injured liver. The effects of the hepatotoxins Escherichia coli lipopolysaccharide (LPS) and CCl4 on histamine synthesis in the liver of mice were evaluated. C3H/HeJ mice were resistant to LPS in including histidine decarboxylase (HDC) in the liver compared with C3H/HeN mice and mast cell-deficient W/Wv mice. However, C3H/HeJ mice did respond strongly to another hepatotoxin, CCl4, leading to a significant increase in HDC activity. CCl4 also caused a marked increase in HDC activity and histamine levels in the liver of W/Wv mice. In addition, injection of CCl4 produced a large increase in the activity of HDC in the spleen and lung of W/Wv mice. HDC activity was confined to the nonparenchymal cells, with parenchymal cells expressing essentially no HDC activity. The CCl4-induced increase in HDC activity was confined, at least in part, to the liver macrophages. These results indicate that the macrophages are responsible for the increase in HDC-dependent histamine production in the liver caused by the injection of hepatotoxins. The possible role of histamine in liver regeneration after injury is discussed.

Endotoxin inhibits glucuronidation in the liver. An effect mediated by intercellular communication

Endotoxin [lipopolysaccharide (LPS) 50 micrograms/mL] added to the perfusion medium increased glucose production and inhibited the glucuronidation of p-nitrophenol in perfused mouse liver both in recirculating and non-recirculating systems, while sulfation of p-nitrophenol was unchanged. The effects of endotoxin could be prevented by the addition of cyclooxygenase inhibitors, while PGD2 and PGE2 also caused a decrease in p-nitrophenol glucuronidation in perfused liver. In isolated hepatocytes endotoxin failed to affect p-nitrophenol conjugation, while PGD2 and PGE2 decreased the rate of it. Our results suggest that endotoxin inhibits glucuronidation through an intercellular communication presumably mediated by eicosanoids.

Non-insulin-like action of sodium orthovanadate in the isolated perfused liver of fed, non-diabetic rats

Vanadium compounds exert insulin-like effects on isolated rat adipocytes and skeletal muscle and improve glucose homeostasis in diabetic rats and mice. However, reports on metabolic actions of vanadium in the liver are still contradictory. Thus, the acute effect of sodium orthovanadate infusion on net glucose production was measured in isolated perfused livers of non-fasting, non-diabetic rats. Continuous infusion (0.2 ml/min; 90 min) of vanadate (10-500 mumol/l) rapidly increased hepatic glucose (p < 0.001), but not cyclic AMP output, reaching peak values after 20 min. The cumulative glucose release displayed concentration dependence with a maximal net effect of 394.3 mumol/100 g body weight and an apparent half-maximal effective vanadate concentration of 19.6 mumol/l. The glycogenolytic response to vanadate was almost completely blocked by 100 mU/l insulin (p < 0.005), by 0.1 mmol/l indomethacin (p < 0.05) and in the absence of Ca2+ (p < 0.001). These results indicate that sodium orthovanadate stimulates glycogenolysis in livers of fed, non-diabetic rats by a Ca(2+)-dependent mechanism, which may involve the release of prostaglandins.

Stimulation of glycogen degradation by prostaglandin E2 in primary cultured rat hepatocytes

Hepatocytes isolated from rats by the collagenase perfusion method were cultured as monolayers at concentrations of 0.4-1.1 x 10(6) attached cells/dish (9 cm2) for 1-3 days and the effect of prostaglandins on their glycogenolysis was studied. By use of [14C]glycogen-labeled cells, prostaglandin E2 (PGE2) was found to have a stimulatory effect on glycogen degradation at high cell density (more than 0.8 x 10(6) cells/dish) in 1-day cultures. PGE2 was maximally effective at 10(-7) M, increasing [14C]release from cellular [14C]glycogen to 2-3 times the basal level after 1 h incubation, and to plateau level within 2 h. PGE1, 16,16-dimethyl PGE2 and PGF2 alpha had similar effects, but PGD2 and dinor-PGE1 (a metabolite of PGE1 and PGE2 in hepatocytes) had no effect. This prostaglandin-induced glycogen degradation was observed in 1-day cultures, with a maximum between 20-30 h, but not in 2-day and later cultures. Treatment of hepatocytes with pertussis toxin potentiated PGE2-stimulated glycogen degradation, indicating that the effect involves a different pathway from that for inhibition of glucagon- and epinephrine-stimulated glycogenolysis by E series prostaglandins reported previously.

Dexfenfluramine treatment influences plasma catecholamines and energy substrate metabolism in rats

The effect of chronic intragastric administration of dexfenfluramine (FFL, 1 mg/kg, twice a day), a drug that increases serotonergic transmission, on peripheral energy substrate metabolism was investigated. Rats were provided with permanent cannulas, allowing stress-free intragastric treatment and blood sampling. Fenfluramine-treated and control animals were submitted to strenuous swimming at days -2, 1, 4, and 7 relative to the onset of FFL treatment at day 0. Blood samples were taken before, during, and after exercise. Thereafter, possible changes in catecholamine sensitivity were investigated during intravenous infusions of norepinephrine (NE) and epinephrine. Finally, energy expenditure, including resting respiratory quotient (RQ), and carbohydrate and fat utilization were measured under baseline conditions. It was found that chronic administration of FFL led to a transient reduction in the exercise-induced increase of blood glucose concentrations. Plasma norepinephrine responses to exercise gradually increased in the FFL-treated animals. Baseline RQ was markedly increased in the FFL-treated animals, indicating an increase of carbohydrate utilization and a decrease of fat combustion. Total energy expenditure remained unchanged. The increased RQ was accompanied by increased sensitivity for NE and significantly decreased baseline concentrations of plasma free fatty acids.

Addition of glucagon to lipid-free total parenteral nutrition reduces production of prostaglandin E2 by stimulated splenic macrophages

Sepsis is a major complication of total parenteral nutrition (TPN). Impaired immunity has been suggested as being responsible for TPN-related sepsis, but it is unknown how the immune system is affected by TPN. We recently found that administration of lipid-free TPN resulted in an increase in prostaglandin E2 (PGE2) release by stimulated splenic macrophages. This observation suggested that TPN may impair immunity through the prominent immunosuppressive effects of PGE2. In the present study, we tested the hypothesis that addition of glucagon to TPN solution may protect against the immunosuppressive effect of TPN by modifying PGE2 secretion. Adult, male Sprague-Dawley rats (n = 18) underwent jugular vein cannulation: group 1 (n = 7) received intravenous saline and chow ad libitum; group 2 (n = 6) received TPN (80 mL/24 h); and group 3 (n = 5) received TPN (80 mL/24 h) plus glucagon (100 micrograms/24 h). After 10 days, spleens were removed and splenic macrophages were isolated and cultured for 24 h in plain M199 medium (nonstimulated) or in medium containing Escherichia coli lipopolysaccharide (5 micrograms/mL) (stimulated). PGE2 release was determined by enzyme-linked immunosorbent assay. There were no differences in PGE2 release between the groups of nonstimulated cells, but when stimulated with lipopolysaccharide, the macrophages from the TPN rats (group 2) released more PGE2 (81.68 +/- 25.99 ng/2.5 x 10(6) cells) than the control group (16.04 +/- 3.26 ng/2.5 x 10(6) cells). The release of PGE2 was normalized in the TPN animals treated with glucagon (15.71 +/- 3.33 ng/2.5 x 10(6) cells). This difference was significant, with p < .05 by Tukey's test after analysis of variance.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of glucose incorporation into glycogen by E-series prostaglandins in cultured rat hepatocytes

In primary cultures of rat hepatocytes, 16,16-dimethylprostaglandin E2 (16,16-dimethyl PGE2), a biologically active analogue of prostaglandin E2 (PGE2), stimulated the basal rate of [14C]glucose incorporation into glycogen. 16,16-Dimethyl PGE2 caused concentration-dependent stimulation (ED50: 10(-8) M) with a maximum 2-3 h after its addition. Prostaglandin E1 (PGE1), PGE2 and prostaglandin F2 alpha (PGF2 alpha) stimulated also the incorporation, but less effectively than 16,16-dimethyl PGE2. However, prostaglandin D2 (PGD2) did not show such effect. Cellular glycogen analysis revealed that PGE2 and 16,16-dimethyl PGE2 increased a net glycogen accumulation time-dependently. Pretreatment of the cultured hepatocytes with pertussis toxin blocked the effects of PGE2 and 16,16-dimethyl PGE2 completely and concentration-dependently. These findings indicate that E-series prostaglandins have significant effects on hepatic glycogenesis via pertussis-toxin-sensitive G protein, in addition to their inhibitory effects on hormone-stimulated glycogenolysis reported previously (Okumura, T., Sago, T. and Saito, K. (1988) Prostaglandins 36, 463-475).

K252a, a potent protein kinase inhibitor, improves endotoxic lethality and glucose dyshomeostasis

To investigate whether the inhibition of protein kinases including protein kinase C can antagonize endotoxicosis, the in vivo effects of K252a, a potent inhibitor of protein kinases, on endotoxin-induced lethality and glucose dyshomeostasis were determined in conscious rats. Sprague-Dawley rats (260-340 g) were divided into the following four groups: Group DS, 2.5% dimethyl sulfoxide (DMSO), 6 ml/kg iv + 0.9% saline, 2 ml/kg iv; group KS, K252a in 2.5% DMSO, 4 mg/kg iv + 0.9% saline; group DE, 2.5% DMSO + endotoxin (E. coli), 15 mg/kg iv; and group KE, K252a in 2.5% DMSO + endotoxin. A quarter of DMSO or K252a solution was continuously infused over a 15 min period before a bolus injection of either saline or endotoxin. The remaining dose was administered over a 180 min period after saline or endotoxin. All animals in the DS and KS groups survived for 24 hrs. K252a significantly improved endotoxic lethality. It attenuated the initial hyperglycemia, and late hypoglycemia, hyperlactacidemia, and base deficit after endotoxin. However, K252a had no influence on the endotoxic alterations of blood pressure, PaCO2 or PaO2. These results suggest that the activations of protein kinases, particularly protein kinase C, are involved in the pathogenesis of lethal endotoxicosis and sepsis.

Prostaglandin E1 (PGE1) attenuates vasoconstriction induced by PGE2, PGD2 and phorbol myristate acetate in the perfused rat liver

It has been shown that prostaglandins (PGs) produced by Kupffer and endothelial cells play an important role in mediating physiological responses to various immunological stimuli. We studied the effect of prostaglandin E1 (PGE1) on the hemodynamic and metabolic changes induced by prostaglandin E2 (PGE2), D2 (PGD2) and phorbol 12-myristate 13-acetate (PMA), a potent inducer of PGs in the isolated rat liver perfused with Krebs-Ringer-bicarbonate (KRB) solution at a constant pressure of 12 cmH2O. The liver was taken from overnight-fasted male Sprague-Dawley rats weighing 260 to 310 g. Both PGE2 and PGD2 significantly decreased hepatic flow when their initial concentration was elevated to micromolar range. Although 1 x 10(-6) M of PGE1 did not have a major effect on hepatic flow, it significantly attenuated the declines of hepatic flow produced by 4 x 10(-6) M of PGE2 and PGD2. However, none of PGs tested influenced glucose and lactate concentrations in the medium. Continuous infusion of PGE1 into the medium at a rate of 5 microg.min(-1) significantly diminished the decreases in hepatic flow and oxygen consumption induced by 2 x 10(-8) M of PMA. These results suggest that administration of PGE1 may preserve hepatic blood flow by modifying the intrahepatic regulatory mechanism involving the activation of Kupffer and endothelial cells.

Calcium-dependent prostaglandin biosynthesis by lipopolysaccharide-stimulated rat Kupffer cells

Isolated rat Kupffer cells produced and released prostaglandin (PG) E2, 6-keto-PGF1 alpha, and thromboxane B2 (TXB2) in response to lipopolysaccharide (LPS) stimulation. This elevation of PGE2, 6-keto-PGF1 alpha and TXB2 in the medium was not observed when cells were cultured in the absence of extracellular calcium or in the presence of an extracellular calcium chelator, EGTA. An intracellular calcium antagonist, TMB-8, also suppressed the production of PGE2, 6-keto-PGF1 alpha and TXB2 in a concentration-dependent manner. The intra-cellular calcium concentration of Kupffer cells elevated early after the addition of LPS determined by the use of fura-2 and a fluorescence microscopy. Moreover, calmodulin inhibitors, W-7 and W-13, apparently inhibited the production of PGF2, 6-keto-PGF1 alpha and TXB2. All these results suggest that LPS-induced PG production by stimulated rat Kupffer cells may be regulated by a calcium-calmodulin pathway.

Enhancement of prostaglandin E2 production by liver macrophages (Kupffer cells) after stimulation with biological response modifiers

PGE2 production by liver macrophages (Kupffer cells) activated by biological response modifiers was examined. Kupffer cells obtained from a normal rat liver possessed cyclooxygenase activity and produced TXB2, PGD2, and PGE2 from (1-14C)arachidonic acid. The major product was PGD2. When Kupffer cells were incubated in the presence of lipo-polysaccharide (LPS), OK-432, or heat-killed Propionibacterium acnes for 24 h, the amount of arachidonate cyclooxygenase products increased and the major product changed from PGD2 to PGE2. When liver macrophages including Kupffer cells were prepared from rats after an injection of LPS, OK-432, or heat-killed P. acnes, it was noticed that the number of cells obtained and PGE2 production increased compared with those of normal rat. These results suggested that PGE2 production by rat liver was induced when they were treated with biological response modifiers.

Endotoxin stimulation of liver parenchymal cell phosphofructokinase activity requires nonparenchymal cells

The rate of carbohydrate flux through phosphofructokinase (measured as the rate of [3-3H]glucose detritiation) was increased fourfold in rat liver parenchymal cells incubated with conditioned medium from lipopolysaccharide-stimulated adherent liver non-parenchymal cells. The rate was not affected in parenchymal cells incubated either with lipopolysaccharide directly or with conditioned medium from non-stimulated non-parenchymal cells. The stimulation of carbohydrate flux through phosphofructokinase by conditioned medium was not duplicated by peptide cytokines known to be released by lipopolysaccharide-activated liver non-parenchymal cells (interleukin-1, interleukin-6, tumor necrosis factor-alpha, and transforming growth factor-beta) or platelet activating factor. Furthermore, formation of the active conditioned medium was not prevented by inclusion of cycloheximide or dexamethasone to inhibit cytokine synthesis, or indomethacin or BW755c to inhibit arachidonic acid metabolism, during lipopolysaccharide-stimulation of the non-parenchymal cells. The results indicate that intercellular communication between lipopolysaccharide-stimulated liver non-parenchymal cells and parenchymal cells by soluble mediators is responsible for the stimulation of liver phosphofructokinase activity during endotoxin-induced shock. Studies to isolate and identify the factor(s) in the conditioned medium are currently in progress.

PAF effects on transmembrane signaling pathways in rat Kupffer cells

Platelet activating factor (PAF) was found to stimulate the metabolism of inositol phospholipids via deacylation and phospholipase C in Kupffer cells, the resident macrophages in liver. PAF-induced phosphoinositide metabolism occurred in two phases. Within seconds after stimulation, in the absence of extracellular Ca++, platelet activating factor caused the phosphodiester hydrolysis of phosphatidylinositol 4,5-bisphosphate and phosphatidylinositol 4-phosphate with the release of inositol 1,4,5-trisphosphate and inositol 1,4-bisphosphate. This was followed by an extracellular Ca(++)-dependent release of glycerophosphoinositol, inositol monophosphates and inositol bisphosphates. Various Ca(++)-mobilizing agonists failed to evoke hydrolysis of phosphoinositides. Platelet activating factor also stimulated the synthesis and release of prostaglandins from these cells. Platelet activating factor-stimulated phosphodiester metabolism of phosphoinositides and prostaglandin synthesis was inhibited by treatment with pertussis toxin and cholera toxin. Pertussis toxin also inhibited platelet activating factor-induced glycerophosphoinositol release. Cholera toxin, in contrast, stimulated platelet activating factor-induced glycerophosphoinositol release and prostaglandin synthesis and synergistically stimulated the effect of platelet activating factor on these processes. The results suggest that platelet activating factor-induced metabolism in the Kupffer cells occurs via specific receptors and may be mediated through the activation of different G-proteins.

Tumor necrosis factor-alpha and interleukin-1 beta production by human fetal Kupffer cells

This study describes the isolation and characterization of human fetal Kupffer cells. We demonstrated that these cells have the potential to respond to cytokines and lipopolysaccharide with an increased production of tumor necrosis factor-alpha and interleukin-1 beta. Kupffer cells were characterized by: (1) morphologic characteristics after adherence to plastic, (2) staining for alpha-naphthyl acetate esterase, (3) immunofluorescence with monoclonal antibodies, and (4) phagocytosis of latex beads. More than 90% of the adherent cells were identified as macrophages. Kupffer cells cultured with lipopolysaccharide were able to produce interleukin-1 beta and tumor necrosis factor-alpha in a time- and dose-dependent fashion and maximal secretion was observed with the use of 10 micrograms of lipopolysaccharide per milliliter within 8 hours of treatment. We have demonstrated mature functional activity of human fetal Kupffer cells at an early gestational age (13 to 19 weeks) and discussed the roles that these cells may play in development and protection of the fetus.

Effect of prostaglandins on glycogenesis and glycogenolysis in primary cultures of rat hepatocytes--a role of prostaglandin D2 in the liver

16,16-Dimethylprostaglandin E2 (dimethylPGE2) increased the incorporation of glucose into glycogen in rat hepatocytes in primary culture and its stimulatory effect was blocked by pretreatment of the cells with pertussis toxin. In contrast, dimethylPGE2, prostaglandin E2 (PGE2) and prostaglandin F2 alpha (PGF2 alpha), but not prostaglandin D2 (PGD2), inhibited glucose incorporation in insulin-induced glycogenesis, and these inhibitory effects were not blocked by pretreatment with pertussis toxin. Prostaglandins and other stimuli (lipopolysaccharide, platelet-activating factor, phorbol ester and zymosan) did not increase the release of [14C]glucose from [14C]glycogen-labeled hepatocytes. On the other hand, under identical conditions except for the presence of glucagon, isoproterenol (beta-adrenergic response) or epinephrine (with propranolol, alpha 1-adrenergic response), dimethylPGE2 and PGE2 inhibited hormone-stimulated glycogenolysis but again PGD2 had no effect.

Fine structure and function of Kupffer cells

Kupffer cells are macrophages that are attached to the luminal surface or inserted in the endothelial lining of hepatic sinusoids. In this site, Kupffer cells play a key role in host defense by removing foreign, toxic and infective substances from the portal blood and by releasing beneficial mediators. Under some conditions, toxic and vasoactive substances also are released from Kupffer cells which are thought to play a role in a variety of liver diseases. Many of these activities may be modulated by the levels of gut derived endotoxin normally present in the portal blood. The ultrastructural aspects of Kupffer cell structure function in situ are best studied using perfused-fixed livers. In fixed livers, transmission and scanning electron microscopy reveal Kupffer cells during health to be irregular in shape with their exposed surfaces presenting numerous microvilli, filopodia, and lamellopodia. Long filopodia penetrate endothelial fenestrae to secure Kupffer cells to the sinusoid lining. Specific membrane invaginations known as worm-like bodies or vermiform processes are seen in the cytoplasm of Kupffer cells as are numerous endocytotic vesicles and lysosomes which vary in density, shape and size. Sometimes, annulate lamellae connected to the rough endoplasmic reticulum also are found. The principal endocytic mechanisms of Kupffer cells are phagocytosis of particulates and cells, and bristle-coated micropinocytosis for fluid-phase endocytosis of smaller substances. Many of these events are mediated by specific receptors. In some species, Kupffer cells can be distinguished from other sinusoidal lining cells and monocytes by specific cytoplasmic staining or monoclonal antibodies. Kupffer cells have been shown to be of monocytic origin as well as having the capacity for self-replication.

Difference in sensitivity to glucagon action in three different rat liver systems

We compared sensitivity to glucagon in three different rat liver systems. In perfused liver, half-maximal response of glycogenolysis was obtained by 5 x 10(-11) mol/L glucagon. In contrast, half-maximal response was obtained by 10(-9) mol/L glucagon in batch incubation of isolated hepatocytes. In perifusion system using the same isolated hepatocytes, 9 x 10(-11) mol/L glucagon induced half-maximal response. In both perfused liver and perifusion system, dose response relationships for glucagon-induced cyclic adenosine monophosphate (cAMP) output were identical. In batch incubation of isolated hepatocytes, again much higher concentration of glucagon was needed to increase cAMP output. Inhibitors of glucagon degradation did not increase the sensitivity of hepatocytes in batch incubation system. When the liver was perfused in recirculation system, glycogenolytic response to glucagon was significantly less than when it was perfused in flow-through system. Also, when extract of lipophilic substances in conditioned medium of batch incubation system was included in perfusate, the glycogenolytic response to glucagon was diminished in perfused liver system. In contrast to the action of glucagon, sensitivities of hepatocytes to calcium mobilizing hormones, phenylephrine, and angiotensin II, in three systems were nearly identical. These results suggest that the diminished sensitivity of hepatocytes to glucagon observed in batch incubation system is due, at least in part, to a substance (or substances) released from hepatocytes.

Hepatic circulation: potential for therapeutic intervention

In recent years, knowledge of the physiology and pharmacology of hepatic circulation has grown rapidly. Liver microcirculation has a unique design that allows very efficient exchange processes between plasma and liver cells, even when severe constraints are imposed upon the system, i.e. in stressful situations. Furthermore, it has been recognized recently that sinusoids and their associated cells can no longer be considered only as passive structures ensuring the dispersion of molecules in the liver, but represent a very sophisticated network that protects and regulates parenchymal cells through a variety of mediators. Finally, vascular abnormalities are a prominent feature of a number of liver pathological processes, including cirrhosis and liver cell necrosis whether induced by alcohol, ischemia, endotoxins, virus or chemicals. Although it is not clear whether vascular lesions can be the primary events that lead to hepatocyte injury, the main interest of these findings is that liver microcirculation could represent a potential target for drug action in these conditions.

Increased liver lipase activity in rats with essential fatty acid deficiency

Liver lipase activity was measured in EFA-deficient rats (long-term) and in control rats and rats fed an EFA-deficient diet for two weeks (short-term). Liver lipase activity was significantly enhanced by EFA deficiency, both in long-term and short-term experiments. The enhanced liver lipase activity could be normalized by feeding these rats normal laboratory chow for 14 days. Since during EFA deficiency prostaglandin synthesis is impaired, the possible involvement of prostaglandins in the observed changes in liver lipase activity during EFA deficiency was studied. Administration of the prostaglandin synthesis inhibitor indomethacin (5 mg/kg body weight, i.p.) to normally fed rats for two days led to an increase of liver lipase activity. Prostaglandin E2 was found to inhibit the secretion of liver lipase activity by freshly isolated parenchymal liver cells in vitro. These results indicate that the increase in liver lipase activity during EFA deficiency may be due to an impairment of the prostaglandin synthesis.

[Regulation of liver functions by autonomic hepatic nerves]

The liver is the glucose reservoir of the organism and moreover an important blood reservoir, which takes up or releases glucose and blood depending on demand. Activation of the sympathetic nerves increases glucose release, shifts lactate uptake to output and reduces a.o. oxygen uptake. Moreover, it elicits a reduction of blood flow, and, by closing of sinusoids, an intrahepatic redistribution as well as a mobilization of blood. Activation of parasympathetic nerves enhances glucose utilization and causes a re-opening of closed sinusoids. The actions of sympathetic nerves can be modulated by hormones. Extracellular calcium as well as the mediators noradrenaline and probably also prostaglandins are involved in the signal chain. Intracellularly the signal chain is propagated by an increase of cytosolic calcium.

Direct activation by prostaglandin F2 alpha but not thromboxane A2 of glycogenolysis via an increase in inositol 1,4,5-trisphosphate in rat hepatocytes

In rat liver prostaglandin F2 alpha (PGF2 alpha) and thromboxane A2 (TXA2), released from non-parenchymal cells, have been implicated as mediators of the enhancement of glucose and lactate output from parenchymal cells caused by sympathetic nerve stimulation [Iwai, M. et al. (1988) Eur. J. Biochem. 175, 45-50]. In isolated rat hepatocytes PGF2 alpha, of which 75% were degraded within 10 min, but not the TXA2 analogue U46619 increased inositol 1,4,5-trisphosphate (IP3), glycogen phosphorylase a activity and glucose output like noradrenaline and vasopressin; cyclic AMP remained unaltered. The maximal increase in IP3 was reached within 20 s and in phosphorylase activity as well as glucose release within 1 min. The results indicate that only PGF2 alpha but not TXA2 can play a role as a direct mediator of the sympathetic metabolic nerve actions in rat liver and that hepatocytes contain also stimulatory prostaglandin receptors linked to phospholipase C in addition to the inhibitory receptors linked to adenylate cyclase known thus far.