Hepatic Output Research Articles

Metabolic effects of the incretin mimetic exenatide in the treatment of type 2 diabetes.

Interventional studies have demonstrated the impact of hyperglycemia on the development of vascular complications associated with type 2 diabetes, which underscores the importance of safely lowering glucose to as near-normal as possible. Among the current challenges to reducing the risk of vascular disease associated with diabetes is the management of body weight in a predominantly overweight patient population, and in which weight gain is likely with many current therapies. Exenatide is the first in a new class of agents termed incretin mimetics, which replicate several glucoregulatory effects of the endogenous incretin hormone, glucagon-like peptide-1 (GLP-1). Currently approved in the US as an injectable adjunct to metformin and/or sulfonylurea therapy, exenatide improves glycemic control through multiple mechanisms of action including: glucose-dependent enhancement of insulin secretion that potentially reduces the risk of hypoglycemia compared with insulin secretagogues; restoration of first-phase insulin secretion typically deficient in patients with type 2 diabetes; suppression of inappropriately elevated glucagon secretion to reduce postprandial hepatic output; and slowing the rate of gastric emptying to regulate glucose appearance into the circulation. Clinical trials in patients with type 2 diabetes treated with subcutaneous exenatide twice daily demonstrated sustained improvements in glycemic control, evidenced by reductions in postprandial and fasting glycemia and glycosylated hemoglobin (HbA(1c)) levels. Notably, improvements in glycemic control with exenatide were coupled with progressive reductions in body weight, which represents a distinct therapeutic benefit for patients with type 2 diabetes. Acute effects of exenatide on beta-cell responsiveness along with significant reductions in body weight in patients with type 2 diabetes may have a positive impact on disease progression and potentially decrease the risk of associated long-term complications.

Influence of platelet activating factor and its antagonist on portal hypertension associated with liver cirrhosis: an experiment with rats

To investigate the influence of platelet activating factor (PAF) and its antagonist BN52021 on portal hypertension associated with liver cirrhosis. Ten SD rats were injected intraperitoneally with carbon tetrachloride to establish a liver cirrhosis model and 10 rats were injected with olive oil as controls. The concentrations of PAF in the blood and liver was examined by rapid (3)H-PAF scintillation proximity assay and the hepatic PAF binding capacity was examined by receptor saturation binding technique. The pressure of portal vein and pressure of femoral artery were measured by intubation method. BN52021 was infused into the portal vein to observe its influence on the blood pressure. The hepatic PAF levels of the cirrhotic rats was 4.0 ng/g +/- 0.4 ng/g, significantly higher than that of the control rats (2.7 ng/g +/- 0.5 ng/g, P < 0.01). The hepatic efflux PAF level of the cirrhotic rats was 6.3 ng/g +/- 0.6 ng/g, significantly higher than that of the control rats (3.4 ng/g +/- 0.6 ng/g, P < 0.01). The hepatic output PAF levels of the cirrhotic rats was 1.0 ng/g +/- 0.6 ng/g, significantly lower than that of the control rats (0.3 ng/g +/- 0.5 ng/g, P < 0.01). The maximum PAF binding capacity of the cirrhotic rats was 2.8 +/- 0.21 fmol/microg protein, significantly higher than that of the control rats (0.9 +/- 0.06 fmol/microg protein, P < 0.01). However, the receptor affinity was not significantly different between these 2 groups. The portal pressure of the cirrhotic rats was 12.2 mm Hg +/- 0.7 mm Hg, significantly higher than that of the control rats (5.3 mm Hg +/- 0.6 mm Hg, P < 0.01). The femoral arterial pressure of the cirrhotic rats was 82 mm Hg +/- 10 mm Hg, significantly lower than that of the control rats (114 mm Hg +/- 9 mm Hg, P < 0.01). Infusion of PAF via the portal vein increased the portal pressure from 12.1 mm Hg +/- 0.6 mm Hg with an increase of 32% (P < 0.01) in the cirrhotic rats, and from 7.7 mm Hg +/- 0.8 mm Hg with an increase of 23%. The PAF response of the cirrhotic rats was 4.1 mm Hg +/- 1.0 mm Hg (227%), significantly higher than that of the control rats (1.8 mm Hg +/- 0.3 mm Hg, P < 0.01). The femoral artery pressure decreased from 82 mm Hg +/- 10 mm Hg to 48 mm Hg +/- 4 mm Hg (P < 0.01) in the cirrhotic rats, and from 114 mm Hg +/- 9 mm Hg to 52 mm Hg +/- 4 mm Hg (P < 0.01). After portal infusion of BN52021 the portal pressure decreased from 14.6 mm Hg +/- 1.6 mm Hg to 12.3 mm Hg +/- 0.8 mm Hg (P < 0.05) with a decrease of 16%, however, did not significantly influenced the femoral arterial pressure in the cirrhotic rats, and did not significantly influenced the portal pressure and femoral arterial pressure in the control rats. The increased hepatic PAF synthesis in cirrhotic is the major source of elevated circulating PAF It upregulates the hepatic hemodynamics that contributes to portal hypertension. The increased portal pressure by endogenous PAF can be decreased to a certain extent by BN52021 which may be used in treatment of portal hypertension.

Role of intestinal sterol transporters Abcg5, Abcg8, and Npc1l1 in cholesterol absorption in mice: gender and age effects

Recent studies have indicated that intestinal cholesterol absorption is a multistep process, which is regulated by multiple genes at the enterocyte level. However, the molecular mechanisms whereby there are gender differences in intestinal cholesterol absorption efficiency and the efficiency of cholesterol absorption increases with age have not yet been fully understood. To explore whether aging increases cholesterol absorption via intestinal sterol transporters, we studied the higher cholesterol-absorbing C57L/J vs. the lower cholesterol-absorbing AKR/J mice at 8 (young adult), 36 (older adult), and 50 (aged) wk of age. To test the hypothesis that estrogen receptor (ER )alpha plays an important regulatory role in cholesterol absorption, we investigated the gonadectomized mice of both genders treated with 17beta-estradiol-releasing pellets at 0, 3, or 6 mug/day and antiestrogenic ICI 182,780 at 125 microg/day. We found that hepatic outputs of biliary cholesterol were significantly increased with age and in response to high levels of estrogen. Aging significantly enhances cholesterol absorption by suppressing expression of the jejunal and ileal sterol efflux transporters [ATP-binding cassette (Abc)g5 and Abcg8] and upregulating expression of the putative duodenal and jejunal sterol influx transporter Npc1l1. Estrogen significantly augmented cholesterol absorption mostly due to an upregulated expression of intestinal Npc1l1, Abcg5, and Abcg8 via the intestinal ERalpha pathway, which can be fully abolished by the antagonist. We conclude that ERalpha activated by estrogen and aging enhances cholesterol absorption by increasing biliary lipid output and mediating intestinal sterol transporters favoring influx of intraluminal cholesterol molecules across the apical membrane of the enterocyte.

Fetal hepatic and umbilical uptakes of glucogenic substrates during a glucagon-somatostatin infusion.

To test the hypothesis that fetal hepatic glutamate output diverts the products of hepatic amino acid metabolism from hepatic gluconeogenesis, ovine fetal hepatic and umbilical uptakes of glucose and glucogenic substrates were measured before and during fetal glucagon-somatostatin (GS) infusion and during the combined infusion of GS, alanine, glutamine, and arginine. Before the infusions, hepatic uptake of lactate, alanine, glutamine, arginine, and other substrates was accompanied by hepatic output of pyruvate, aspartate, serine, glutamate, and ornithine. The GS infusion induced hepatic output of 1.00 +/- 0.07 mol glucose carbon/mol O(2) uptake, an equivalent reduction in hepatic output of pyruvate and glutamate carbon, a decrease in umbilical glucose uptake and placental uptake of fetal glutamate, an increase in hepatic alanine and arginine clearances, and a decrease in umbilical alanine, glutamine, and arginine uptakes. The latter result suggests that glucagon inhibits umbilical amino acid uptake. We conclude that fetal hepatic pyruvate and glutamate output is part of an adaptation to placental function that requires the fetal liver to maintain both a high rate of catabolism of glucogenic substrates and a low rate of gluconeogenesis.

Effect of 6 dietary fatty acids on the postprandial lipid profile, plasma fatty acids, lipoprotein lipase, and cholesterol ester transfer activities in healthy young men

There is increasing evidence that postprandial triacylglycerol-rich lipoproteins may be related to atherogenic risk. The objective was to investigate the effect of individual fatty acid intakes on postprandial plasma lipoprotein triacylglycerol and cholesterol concentrations, plasma fatty acids, and preheparin lipoprotein lipase and cholesterol ester transfer protein (CETP) activities. Six test fats high (approximately 43% by wt) in stearic acid, palmitic acid, palmitic + myristic acid, oleic acid, elaidic acid (trans 18:1), and linoleic acid were produced by interesterification. After having fasted for 12 h, 16 healthy young men were served the individual test fats incorporated into meals (1 g fat/kg body wt) in random order on different days separated by washout periods. Blood samples were drawn before and 2, 4, 6, and 8 h after the meals. Different responses to the test-fat meals were observed for plasma lipoprotein triacylglycerol and cholesterol concentrations, plasma fatty acid concentrations, and lipoprotein lipase and CETP activities (diet x time interaction: 0.001 < P < 0.05). Intake of the long-chain saturated fatty acids stearic and palmitic acids resulted in a relatively lower lipemic response than did intake of the unsaturated fatty acids, probably because the saturated fatty acids were absorbed less and at a lower rate; therefore, the lipemic response took longer to return to postabsorptive values. Fatty acid chain length and degree of saturation appear to affect the extent and duration of lipemia and affect hepatic output indirectly. These effects may not be mediated via effects on lipoprotein lipase and CETP activities.

Enhancement of Jejunal Absorption of Conjugated Bile Acid by Neurotensin in Rats

Release of neurotensin (NT) from intestines is markedly stimulated by ingested fat, and NT may facilitate lipid digestion and absorption through various actions that are not fully understood. Our recent finding that NT stimulates hepatic output of bile acids only when bile delivery to the intestine is maintained has led us to investigate the effects of NT on bile acid absorption in the rat small intestine. We measured the effects of intravenous infusion of NT (3-10 pmol x kg(-1) x min(-1)) on biliary recovery of (3)H-taurocholate ((3)H-TC) and (3)H-cholate administered into proximal and distal intestines or into isolated intestinal segments in situ in biliary fistula rats. To further understand the underlying mechanisms involved, the effects of NT on intestinal absorption of (3)H-D-glucose, (3)H-leucine, (14)C-antipyrine, and (51)Cr-EDTA were investigated by monitoring the absorption of radioactivity into superior mesenteric venous blood. Infusion of NT, at doses that caused near physiologic increases in blood NT levels, increased biliary recovery of (3)H-TC from the jejunum (3.4-fold) and ileum (1.7-fold), but did not enhance absorption of (3)H-cholate. NT also facilitated transcellular uptake of (3)H-glucose and (3)H-leucine and increased paracellular uptake to (51)Cr-EDTA and (3)H-mannitol, but did not alter the absorption rate for (14)C-antipyrine. These results indicate that NT can exert a facilitative effect on intestinal bile acid absorption and return to liver. This effect of NT may involve increases in paracellular absorption and carrier-mediated transport by mechanisms not yet identified.

The glitazones: proceed with caution.

Type 2 diabetes mellitus is characterized by the early onset of insulin resistance. Reduced, responsiveness to normal circulating levels of insulin leads to hyperinsulinemia. When the pancreas is unable to keep up with increased insulin requirements, hyperglycemia ensues. This can influence the development of diabetes mellitus, obesity, hypertension, and dyslipidemia.1,2,3Commonly referred to as “syndrome X,” these complications are associated with an increased risk of coronary heart disease. A new class of drugs, the glitazones, offers the first therapeutic option specifically targeting insulin resistance. The drugs act on tissues such as liver and skeletal muscle, sensitizing them to insulin action, and thereby increasing glucose uptake and decreasing its hepatic output.

Disposition of a Mixed Meal by Conscious Dogs after Seven Days of Treatment with Cyclosporine A and Prednisone

Combination immunosuppressive therapy, that often includes prednisone and cyclosporine A (CyA), is commonly used in the treatment of organ transplant patients. We hypothesized that CyA and prednisone treatment would alter the roles of the liver and peripheral tissues in the disposal of carbohydrates from a meal. Using the arteriovenous difference technique, we examined the disposition of an intragastrically delivered mixed meal in eight 24-hour fasted conscious dogs that had received CyA 15 mg x kg(-1) daily and prednisone 5 mg twice daily for 7 consecutive days before study (CyA-prednisone group). The results were compared with those from a group of 13 dogs (control group) receiving the same meal but no drugs. Neither arterial blood glucose concentrations nor arterial plasma insulin or glucagon concentrations differed significantly between the groups at any time. Cumulative net gut glucose output was equivalent to 43 +/- 9 vs 57% +/- 7% of the glucose in the meal in CyA-prednisone vs control (p = .12). The CyA-prednisone group exhibited greater (p < .05) mean net hepatic glucose uptakes (15.4 +/- 4.6 vs 4.3 +/- 2.2 micromol x kg(-1) x min(-1) and net hepatic fractional extractions of glucose (7.8 +/- 1.6 and 1.5% +/- 1.0%) than the control group. Arterial blood lactate concentrations and net hepatic lactate output were greater in the CyA-prednisone group than the control group (p < .05). Hepatic glycogen content at the end of the study was 2.5-fold greater in the CyA-prednisone group than in the control group (p < .05). The nonhepatic tissues disposed of approximately 91% of the absorbed glucose in the control group but only approximately 26% in the CyA-prednisone group (p < .05). CyA-prednisone treatment caused a marked shift in the carbohydrate disposal from a meal, enhancing the hepatic glucose uptake and decreasing peripheral glucose disposal.

Effect of dexamethasone on fetal hepatic glutamine-glutamate exchange.

Intravenous infusion of dexamethasone (Dex) in the fetal lamb causes a two- to threefold increase in plasma glutamine and other glucogenic amino acids and a decrease of plasma glutamate to approximately one-third of normal. To explore the underlying mechanisms, hepatic amino acid uptake and conversion of L-[1-(13)C]glutamine to L-[1-(13)C]glutamate and (13)CO(2) were measured in six sheep fetuses before and in the last 2 h of a 26-h Dex infusion. Dex decreased hepatic glutamine and alanine uptakes (P < 0.01) and hepatic glutamate output (P < 0.001). Hepatic outputs of the glutamate (R(Glu,Gln)) and CO(2) formed from plasma glutamine decreased to 21 (P < 0.001) and 53% (P = 0.009) of control, respectively. R(Glu,Gln), expressed as a fraction of both outputs, decreased (P < 0.001) from 0.36 +/- 0.02 to 0.18 +/- 0.04. Hepatic glucose output remained virtually zero throughout the experiment. We conclude that Dex decreases fetal hepatic glutamate output by increasing the routing of glutamate carbon into the citric acid cycle and by decreasing the hepatic uptake of glucogenic amino acids.

The importance of rapid insulin secretion: revisited.

259 IN THE PRECEDING ARTICLE ENTITLED, “Pharmacokinetics, Pharmacodynamics, and DoseDependent Relationship of Repaglinide in Type 2 Diabetes” (page 247), Dr. Strange and associates describe some of the characteristics and advantages of the relatively fast acting, oral beta-cell-stimulant, repaglinide. The study illustrates an important principle of insulin/ glucose kinetics that was well recognized in the early 1970s and is just now becoming clinically applicable. This principle emphasizes that the time of insulin provision can be as important for glucose homeostases as the total insulin provided. Insulin and glucose form a closed loop system, in which glucose stimulates insulin secretion and insulin increases glucose uptake and reduces circulating glucose levels, thereby reducing further secretion. However, the time frames for these two phenomena are significantly different. As shown in early studies using the in vitro perfused pancreas,1 insulin secretion increases within 15 seconds of a rise in glucose levels. In contrast, 8–15 minutes are required for insulin to reach its target tissues and activate sufficient glucose uptake and metabolism in muscle and fat (or decrease hepatic output from the liver) to change the circulating glucose level. Predictably, in such a closed loop system, if insulin secretion is regulated only by the concentration of glucose, insulin release increases with a rising glucose before insulin reaches and becomes effective at its target sites. Even when, in time, tissue insulin is adequate to cause a peaking and partial decline in blood glucose, insulin secretion at these elevated glucose levels continues. When glucose levels reach basal, insulin secretion returns to normal, but tissue insulin levels are excessive. Therefore, if the beta cell only recognizes the concentration of glucose, a resulting delayed hypoglycemia is inevitable. Recognition of the inadequacy of a simple relationship between glucose concentration and insulin secretion was shown clearly 25 years ago with the development of an experimental “Artificial pancreas.”2 (This was not a portable sustainable device but a large bedside apparatus to which the subject was briefly connected by intravenous catheters.) Algorithms containing only a glucose concentration dependency, when providing sufficient insulin to produce a normal rise in glucose, overinsulinized the tissues and could not prevent subsequent hypoglycemia. Only when an algorithm was added with a glucose rate-of-change component could near perfect control be achieved. Most interestingly, when insulin was provided rapidly to meet the rising glucose, only one-tenth the amount of insulin was required to achieve control! Although a reliable closed-loop, portable artificial pancreas is not yet available, it is probable that only minor refinements of the algorithms developed decades ago will be adaptable. To avoid overinsulinization, the normal pancreas also utilizes a form of glucose-rate sensitivity. In 1968,1 it was shown that the pancreas Analysis

Regulation of porcine biliary secretion by secretin.

The importance of physiological plasma levels of secretin in biliary bicarbonate secretion is not known. However, in anaesthetized pigs the substantial hepatic output of bicarbonate into the duodenum in response to low doses of secretin exceeds pancreatic bicarbonate output. The aim was therefore to study the relationship between duodenal acidification, secretin and hepatic biliary bicarbonate output in the conscious pig. Göttingen minipigs (n = 22) were cholecystectomized and the common bile duct catheterized. The biliary bicarbonate secretion in response to intraduodenal HCl, secretin or pentagastrin given intravenously, and to meal was studied. Intraduodenal HCl infusion, secretin and pentagastrin given intravenously augmented hepatic bicarbonate output and plasma secretin concentrations significantly. The secretin response to acidification was sufficient to explain the subsequent increase in biliary bicarbonate secretion. Hepatic bicarbonate secretion and concentrations of CCK and secretin in plasma increased postprandially. Exclusion of bile salts from the duodenum abolished postprandial increase in bile volume and increased release of CCK in fasting and fed pigs whereas secretin release was diminished. The results demonstrate that hepatic bicarbonate secretion is stimulated by endogenous secretin and therefore may have a physiological role in duodenal neutralization.

Metabolic alterations in the fetal hepatic and umbilical circulations during glucocorticoid-induced parturition in sheep.

Fetal hepatic amino acid metabolism has unique features in comparison to postnatal life. Thus, it seemed likely that this metabolism might be changed by the endocrine changes which precede birth. To explore the changes in placental and fetal carbohydrate and amino acid metabolism that occur during parturition, labor was induced in six ewes at 131 +/- 1 d gestation with a fetal infusion of dexamethasone. For purpose of chemical analysis, blood was withdrawn before and approximately 3 and 25 h from the start of the infusion from maternal arterial, uterine venous, umbilical venous, fetal arterial, and left hepatic venous catheters. Fetal oxygenation remained normal. At 25 h, both fetal and maternal arterial plasma glucose concentrations increased (p < 0.01 and p < 0.02, respectively) and umbilical glucose uptake decreased (p < 0.05). Fetal glutamate showed a significant reduction in its hepatic output (p < 0.05) with a concomitant reduction in fetal arterial plasma concentration (p < 0.05) and placental uptake (p < 0.01). Fetal plasma concentrations of several other amino acids were markedly increased. The reduction in placental glutamate uptake was temporally associated with a decline in progesterone release by the pregnant uterus. These data suggest the hypothesis that glutamate plays a role in integrating the complex changes in placental and fetal hepatic metabolism that occur during parturition.

Pituitary and adrenals are required for hyperglycemic reflex initiated by stimulation of CBR with cyanide.

We have previously shown that stimulation of carotid body receptors (CBR) with sodium cyanide (NaCN) elicits a rapid hyperglycemic reflex. Here we explore whether the pituitary and adrenals, two glands involved in glucose homeostasis, are necessary for this reflex. Experiments were performed on anesthetized rats that were artificially ventilated. Measurements of hepatic venous-arterial glucose difference indicated that CBR stimulation with a bolus of 5 micrograms/100 g NaCN produced an immediate increase in the output of glucose by the liver. The same dose of NaCN failed to increase hepatic output of glucose in rats with bilateral adrenalectomy or in rats 1 wk after surgical removal of neurohypophysis. Reflex glucose output by the liver was maintained after adenohypophysectomy or in adrenalectomized rats after adrenal autotransplantation to epiploon. Measurements of epinephrine in plasma and in the grafted adrenal tissue showed that the adrenal autograft can store and secrete catecholamines Immunocytochemical observations indicated that the grafted adrenals retain medullary cells. These results indicate that neurohypophysis and adrenals are necessary for the hyperglycemic reflex initiated by CBR stimulation with NaCN and that the participation of these two organs in this reflex is probably humoral.

Neural and pancreatic influences on net hepatic glucose uptake and glycogen synthesis.

The role of the liver nerves in the disposition of peripherally administered glucose was examined in seven hepatic innervated (HI) and nine hepatic denervated (HD) 42-h-fasted conscious dogs. After a 40-min basal period, there was a 4-h experimental period during which the hepatic glucose load was increased twofold via peripheral glucose infusion. Somatostatin was infused to suppress pancreatic endocrine secretion, and insulin and glucagon were infused intraportally to produce a fourfold increase in insulin and a gradual decrease (approximately 25%) in glucagon. The area under the curve of net hepatic glucose uptake (NHGU) during the glucose infusion period totaled 483 +/- 82 and 335 +/- 32 mg/kg in HD and HI, respectively (P < 0.05). The area under the curve of the hepatic fractional extraction of glucose was 27% greater in HD (P < 0.05). Net hepatic lactate output was similar in the two groups, and net hepatic glycogen synthesis was 3.8 +/- 0.8 vs. 2.7 +/- 0.5 mg.kg dog wt-1.min-1 in HD and HI, respectively (P = 0.13). The direct pathway of glycogen synthesis was responsible for 54-58% of net hepatic glycogen synthesis in both HI and HD (n = 6 for both). In summary 1) NHGU in response to peripheral glucose infusion was approximately 44% greater in HD than in HI, 2) net hepatic glycogen synthesis was enhanced by 41% in HD although the probability of this change was 0.13, and 3) the contribution of the direct pathway to glycogen synthesis was the same in HD and HI. These data are consistent with a role for the liver nerves in regulating the magnitude of NHGU in response to glucose administration. They also indicate that the absence of liver nerves may reduce glycogen turnover during glucose infusion.

Role of insulin and proinsulin in diabetic vascular disease

Associations between loss of glucose tolerance, insulin resistance, and ischemic heart disease (IHD) are of great current concern. Considerable controversy and uncertainty relates to the mechanism(s) that underlies these associations. Whilst there is some evidence in prospective studies of an association between hyperinsulinemia and future IHD, it is by no means strong or consistent between different studies. Hypertriglyceridemia is another possible factor involved in the linkage between glucose intolerance and IHD. There is good evidence for an affect of plasma nonesterified fatty acids (NEFA) to increase hepatic output of VLDL. Insulin, contrary to some suggestions, acts to lower plasma VLDL by actions directly on hepatic output and activation of adipose tissue lipoprotein lipase, and indirectly via the hormones affect of lowering plasma NEFA. Glycosylation and oxidation of lipoproteins may enhance their atherogenic potential. It is highly probable that procoagulant changes are also important processes predisposing to IHD. Associations between plasminogen activator inhibitor-1 and insulin, intact and 32,33 split proinsulin hypertriglyceridemia, and insulin resistance have been reported, but a unifying hypothesis explaining these links remains elusive. Epidemiological studies now repeated in a number of centers have shown links between infant mortality and birth weight and risk of IHD, and between birth weight and risk of impaired glucose tolerance and non-insulin-dependent diabetes mellitus (NIDDM). It has been proposed, therefore, that impairment of fetal and infant growth may underlie the associations between loss of glucose tolerance and risk of IHD. Animal models form the basis of much current research to test this concept.

Homeostatic regulation of hepatocyte nuclear transcription factor 1 expression in cultured hepatoma cells.

Serum colloid osmotic pressure is believed to control the hepatic output of plasma proteins, including albumin. The present study was aimed at identifying the molecular basis for feedback control of albumin gene expression in highly differentiated hepatoma cells. The steady-state level of albumin mRNA and the activity of a 282-bp albumin promoter-chloramphenicol acetyltransferase reporter gene in cells incubated in the presence of increasing amounts of serum albumin or dextran were significantly and selectively decreased. When nuclear extracts from cells exposed to 5% (wt/vol) serum albumin were tested in a gel-retardation assay with six oligonucleotide probes containing DNA elements of the albumin promoter, only the element B-retarded band, which contains the nucleotide recognition sequence for hepatocyte nuclear transcription factor 1 alpha (HNF-1 alpha), was consistently decreased as compared to nuclear extract from cells not exposed to serum albumin. Moreover, the activity of a reporter gene with a basal TATA-promoter driven by multiple HNF-1 alpha recognition elements was selectively inhibited in cells incubated in the presence of 5% serum albumin. A reduction of HNF-1 alpha mRNA appears to be responsible for this response to a change in the level of macromolecules in the incubation medium. These results indicate that activity of a dominant liver transcription factor, HNF-1 alpha, controlling the transcription of several liver-specific genes, is modulated by a fluctuation in the level of oncotically active macromolecules.

Effect of ursodeoxycholic acid on hepatic cholesterol metabolism.

Oral administration of ursodeoxycholic acid (UDCA) renders bile unsaturated with cholesterol by reducing the hepatic output of cholesterol. Theoretically, several mechanisms may be of importance. In the present overview, the effect of treatment with UDCA on hepatic cholesterol metabolism is evaluated, in particular the influence on hepatic cholesterol synthesis, 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase activity, bile acid synthesis, 7 alpha-hydroxylation of cholesterol, and esterification of cholesterol--acyl coenzyme A: cholesterol acetyltransferase (ACAT) activity. It is apparent that UDCA treatment does not inhibit the hepatic HMG CoA reductase activity. Neither is ACAT activity or the cholesteryl ester content changed by UDCA. The catabolism of cholesterol to bile acids is unaffected or slightly increased during administration of UDCA. It is concluded that a stimulated degradation of cholesterol to bile acids may partly explain the decrease in hepatic secretion of cholesterol obtained during UDCA administration. It is suggested that the reduction in cholesterol absorption from the intestine seen during UDCA therapy may also be of importance.

Tumor necrosis factor-alpha produces hepatocellular dysfunction despite normal cardiac output and hepatic microcirculation

Although plasma levels of tumor necrosis factor (TNF) are elevated and hepatocellular dysfunction occurs even in the early hyperdynamic stage of sepsis, the precise mechanism responsible for this dysfunction remains unknown. Although TNF at high doses produces circulatory failure, it is not known whether the dose of TNF that does not adversely affect hemodynamics alters hepatocellular function. To study this, recombinant murine TNF-alpha was infused intravenously (0.05 or 0.25 mg/kg) over 30 min in normal rats. At 1 and 4 h after infusion of TNF-alpha or an equivalent volume of saline, hepatocellular function [i.e., maximum velocity (Vmax) and Michaelis constant (Km)] was assessed using in vivo indocyanine green clearance without blood sampling. Additional parameters measured were as follows: cardiac output by dye dilution, hepatic microcirculation by laser Doppler flowmetry and colloidal carbon infusion, plasma TNF and interleukin-6 (IL-6) by cytokine-dependent cellular assays, and plasma glucose enzymatically. The results indicate that although infusion of 0.05 mg/kg TNF-alpha did not affect Vmax and Km, its infusion at 0.25 mg/kg produced a significant depression of hepatocellular function and markedly increased the synthesis and/or release of IL-6. TNF-alpha-induced hepatocellular dysfunction was not associated with any significant changes in hepatic microcirculation, plasma glucose, cardiac output, and other measured hemodynamic parameters. Thus hepatocellular dysfunction observed after TNF infusion may be due to the direct effect of this cytokine alone or in combination with IL-6.

Acetaldehyde adducts and autoantibodies against VLDL and LDL in alcoholics

Alcohol consumption markedly increases the hepatic output of very low density lipoprotein (VLDL), whereas it decreases the resulting low density lipoprotein (LDL) levels and apolipoprotein B. As ethylation of apoB-lysine renders LDL immunogenic and accelerates their clearance, and as alcoholics develop antibodies against acetaldehyde-protein adducts, we searched for antibodies against lipoproteins. We measured serum IgG, IgA, and IgM titers against VLDL, LDL and high density lipoprotein (HDL) in 10 non-alcoholics and 35 recently drinking alcoholics by ELISA assay. Alcoholics had higher IgG titers than non-alcoholics against VLDL and LDL; these were higher with VLDL than LDL or HDL. Using VLDL and LDL (but not HDL) from alcoholics gave the greatest response. There was no difference in IgA and IgM reactivity. To search for acetaldehyde adducts, we measured the reactivity of VLDL, LDL, HDL, and residual serum proteins against a rabbit anti P4502E1-acetaldehyde adduct IgG, which recognizes the adducts but not the unmodified proteins (except for P4502E1). ApoB-containing lipoproteins from alcoholics (and to a lesser extent non-lipoprotein proteins) reacted with anti-adduct IgG more strongly than those of non-alcoholics. The difference was striking for VLDL, less for LDL, and not detectable for HDL. This suggests that acetaldehyde reacts with apoB prior to its secretion from the liver and that the altered VLDL are partially removed prior to their conversion to LDL. In conclusion, alcoholics develop acetaldehyde adducts in apoB-containing lipoproteins, particularly VLDL. The immune response to these neoantigens could result in accelerated clearance of VLDL and LDL and decreased conversion of VLDL to LDL.

Neural modulation of canine duodenal bile acid delivery in the interdigestive and postprandial periods

The neural modulation of gallbladder filling-emptying and duodenal delivery of canine hepatic biliary output was studied in conscious dogs using transient cold blockade or transection of the cervical vagosympathetic nerves previously isolated in skin loops on either side of the neck. Gallbladder filling-emptying was defined as the algebraic difference between a steady-state rate of hepatic secretion [established by a continuous intravenous infusion of [14C]taurocholic acid (TCA)] and the duodenal rate of delivery of [14C]TCA (measured by duodenal marker perfusion). Duodenal motility was recorded manometrically. Experiments in the fasted and fed state were performed under control conditions, during cold blockade, and after transection of the cervical vagosympathetic nerves. Under control conditions: 1) during fasting, the majority of hepatic [14C]TCA output was stored in the gallbladder during the first half of the migrating myoelectric complex (MMC). An increased rate of duodenal delivery and partial gallbladder emptying occurred before phase III of the MMC. 2) Feeding induced an immediate increase in duodenal bile acid delivery and gallbladder emptying. After cold blockade or transection: 1) partial gallbladder emptying before phase III of the MMC was abolished. 2) The immediate postprandial increase in duodenal bile acid delivery and gallbladder emptying was abolished even when the animal received a continuous duodenal infusion of the duodenal aspirate of another fed animal (to control for the effect of impaired gastric emptying after cold blockade). In addition, cold blockade significantly reduced the effect of an exogenous infusion of cholecystokinin octapeptide on gallbladder emptying. These results suggest that neurons in the canine cervical vagosympathetic nerves play a major role in the regulation of rhythmic partial emptying of the gallbladder in the interdigestive period, coordinate a cephalic phase of postprandial gallbladder emptying, and are important in mediating the effects of cholecystokinin on the gallbladder during the gastric and enteric phases of postprandial gallbladder emptying.