Ventral neural tube cells differentiate into hepatocytes in the chick embryo

A population of ventral neural tube cells has recently been shown to migrate out of the hind brain neural tube via the vagus nerve and contribute to the developing gastrointestinal tract. Since liver is also innervated by the vagus nerve, we sought to determine if these cells also migrate into the liver. Ventral neural tube cells in the caudal hindbrain of chick embryos were tagged with a replication-deficient retroviral vector containing the LacZ gene on embryonic day 2. Embryos were processed for detection of labeled cells on embryonic day 5 and 11. Labeled cells were seen in the liver on both days and identified as hepatocytes. Previously, it was believed that all hepatocytes develop from the gut endoderm. Results of the present study show an additional source for the formation of liver cells. Received 25 August 1998; received after revision 5 November 1998; accepted 5 November 1998     

Pressure acclimation of the eel and liver membrane composition

Homeoviscous adaptation of membrane fluidity is known to exist in fish living at great depths. Is this adaptation also present in fish living near the surface but experimentally acclimated to high pressure? The composition of mitochondria-rich fractions extracted from the livers of eels acclimated for 15 days at 101 ATA was determined. The results show that pressure induced a significant increase (+100%) of total phospholipids (PL) and cholesterol without a change in their ratio. The increase of PL content was accompanied by a decrease in phosphatidylcholine in favour of phosphatidyl ethanolamine which, due to its preference for the H₁₁ form, is able to compensate for the loss in fluidity induced by pressure.     

Autophagy and lysosomal proteolysis in the liver

Summary Autophagy is defined as any process whereby cellular macromolecules destined for degradation gain access to the lysosomes. A review is presented on the physiological significance, mechanisms and regulation of autophagy in hepatocytes, concentrating on the issue of regulation. The article ends by discussing techniques available for future research.     

Effects of acetaldehyde and/or ethanol on neutral amino acid transport systems in microvillous brush border membrane vesicles prepared from human placenta

Summary At 20 mM of acetaldehyde, the activities of three transport systems of L-alanine distinguished by the difference in their cation dependence, namely 1) Na⁺-specific, 2) Li⁺-dependent, and 3) Na⁺-independent systems, were significantly reduced in a similar manner. Only the Li⁺-dependent system was selectively inhibited at toxic concentrations of acetaldehyde and ethanol.     

Emerging roles of the oxysterol-binding protein family in metabolism, transport, and signaling

OSBP (oxysterol-binding protein) and ORPs (OSBP-related proteins) constitute an enigmatic eukaryotic protein family that is united by a signature domain that binds oxysterols, sterols, and possibly other hydrophobic ligands. The human genome contains 12 OSBP/ORP family members genes, while that of the budding yeast Saccharomyces cerevisiae encodes seven OSBP homologues (Osh). Of these, Osh4 (also referred to as Kes1) has been the most widely studied to date. Recently, three-dimensional crystal structures of Osh4 with and without sterols bound within the core of the protein were determined. The core consists of 19 anti-parallel β-sheets that form a near-complete β-barrel. Recent work has suggested that Osh proteins facilitate the non-vesicular transport of sterols in vivo and in vitro, while other evidence supports a role for Osh proteins in the regulation of vesicular transport and lipid metabolism.This article will review recent advances in the study of ORP/Osh proteins and will discuss future research issues regarding the ORP/Osh family. Received 17 July 2007; received after revision 14 August 2007; accepted 12 September 2007     

Hormonal control of manganese transport in the mouse thyroid

The present study deals with a possible mechanism controlling the transport of manganese (Mn), an essential trace element, from the circulation to the thyroid. Mice were pretreated with propylthiouracil (PTU) or triiodothyronine (T₃), and a measurement of the thyroid:serum concentration ratio (T/S) of radioactive manganese (⁵⁴Mn) was carried out. The T/S of⁵⁴Mn was greatly enhanced by PTU, but reduced by T₃. Several methods were used to demonstrate that the T/S of⁵⁴Mn depends upon the level of thyroid-stimulating hormone (TSH) in the serum. First, bovine TSH was injected into mice; an increase in the T/S resulted. Secondly, serum thyroxine and T₃ levels measured by radioimmunoassay (RIA) suggested that PTU produced an increase in serum TSH and T₃ a decrease. However, direct measurement of mouse TSH by RIA for rat TSH failed to produce proof of any changes in TSH level, owing to poor cross-reactivity. Taking all the information into account, it is concluded that Mn-transport into the thyroid is controlled by the thyroid state.     

Occurrence of polyploidy and multinuclearity in the differentiating liver of chick embryo

Summary Increase in nuclear size in liver has been used as an index of polyploidy. It has long been considered that the occurrence of polyploidy and multinuclearity are characteristics of mammalian liver. The present study shows the occurrence of these phenomena in the liver of birds, so these features are not confined to mammals. 3 classes of nuclear size groups have been identified. The simultaneous occurrence of polyploidy and binuclearity indicates some sort of interrelationship between them.     

Immunoquantitation of some cytochrome P-450 isozymes in liver microsomes from streptozotocin-diabetic rats

Summary Streptozotocin-diabetes in rats leads to a decrease of cytochrome P-450 UT-A (the major form in control rats) and an increase of cytochrome P-450 PB-B (the major one induced by phenobarbital treatment) in liver microsomes. The increased benzphetamine-N-demethylase activity can be related to the induction of cytochrome P-450 PB-B.     

Inhibition of the sodium pump does not cause a stoichiometric decrease of ATP-production in energy limited fish hepatocytes

In isolated goldfish hepatocytes underaerobic conditions the energy requirement for the sodium pump (calculated from Rb⁺ flux) is closely matched by the ouabain-sensitive fraction of oxygen consumption, whereas during in vitroanoxia (cyanide inhibition of the electron transport chain) the measured ATP demand of the sodium pump clearly exceeds ouabain-sensitive ATP production by anaerobic glycolysis. We conclude that when the energy status of cells is low, part or all of the ATP spared by the inhibition of a particular function may be used for fuelling other ATP-consuming functions.     

Net transport of cholesterol from cells of the human EA.hy 926 endothelial cell line to high density lipoproteins

EA.hy 926 cells, a human endothelial cell line, show characteristics of differentiated endothelial cells. The cells express saturable binding of apo E-free¹²⁵I-high density lipoprotein₃ (HDL₃). B_max increased from 71 to 226 ng HDL₃ bound/mg cell protein after cholesterol loading of the confluent endothelial cells with cationized low density lipoprotein (LDL). The affinity did not change after cholesterol enrichment (K_d was 37 g HDL₃ protein/ml for control cells and 31 g/ml, for loaded cells). Incubation of cholesterol-loaded EA.hy 926 cells with native HDL and LDL had different effects on cellular cholesterol levels. Incubation with HDL decreased both esterified and unesterified cellular cholesteryl, but LDL did not change total cellular cholesterol However, LDL tended to increase cellular cholesteryl esters, with a concomitant decrease of unesterified, cellular cholesterol. Incubation of endothelial cells with both HDL and LDL also resulted in decreased total cellular cholesterol levels. These data show that cationized LDL-loaded human endothelial EA.hy 926 cells can be used to study the net transport of cellular cholesterol to HDL, the first step in reverse cholesterol transport.     

Axonal transport of neurofilaments in normal and disease states

Neurofilaments are among the most abundant organelles in neurones. They are synthesised in cell bodies and then transported into and through axons by a process termed 'slow axonal transport' at a rate that is distinct from that driven by conventional fast motors. Several recent studies have now demonstrated that this slow rate of transport is actually the consequence of conventional fast rates of movement that are interrupted by extended pausing. At any one time, most neurofilaments are thus stationary. Accumulations of neurofilaments are a pathological feature of several human neurodegenerative diseases suggesting that neurofilament transport is disrupted in disease states. Here, we review recent advances in our understanding of neurofilament transport in both normal and disease states. Increasing evidence suggests that phosphorylation of neurofilaments is a mechanism for regulating their transport properties, possibly by promoting their detachment from the motor(s). In some neurodegenerative diseases, signal transduction mechanisms involving neurofilament kinases and phosphatases may be perturbed leading to disruption of transport. Received 11 July 2001; received after revision 30 August 2001; accepted 31 August 2001     

Smooth muscle in the hepatic artery,portal vein and hepatic vein within the liver of the raccoon and guinea pig

Summary The amount and arrangement of smooth muscle in the intrahepatic vessels suggests that the guinea pig would be a good animal model for studying mechanisms controlling intrahepatic portal vein blood flow, while the raccoon would be good for studying hepatic vein mechanisms of control.     

Development and hormonal control of thioredoxin and the thioredoxin-reductase system in the rat liver during the perinatal period

Summary The development and hormonal regulation of thioredoxin and of the thioredoxin-reductase system were investigated during the perinatal period in rat liver. An immunological procedure was developed in order to quantify thioredoxin in fetal and neonatal hepatocytes. Both immunoreactive thioredoxin and thioredoxin-reductase activity appeared on day 16.5 of pregnancy. The level of immunoreactive thioredoxin increased during the late fetal period, and its level was the same 24 h after birth. Moreover, its development was not subjected to hormonal regulation by corticosteroids and glucagon. In contrast, thioredoxin-reductase activity increased 3 times during the late fetal period and presented a marked increase 24 h after birth. In the absence of glucocorticoids there was no increase in the level of thioredoxin reductase, while administration of hydrocortisone acetate and glucagon to fetuses prematurely evoked its activity. This study suggests that if thioredoxin acts physiologically, this activity is related to the state of reduction of the molecule rather than to the total concentration in the liver.     

Combined axonal transport tracing and immunocytochemistry for mapping pathways of peptide-containing nerves in the peripheral nervous system

Summary The various combinations of axonal transport tracing and immunocytochemistry used for mapping pathways of peptide-containing nerves, and in particular those of the peripheral nervous system, are reviewed. The advantages and disadvantages of these methods are discussed. The applications and results presented illustrate the future potential value of this approach.     

Glucose formation from methylglyoxal in hepatocytes from streptozotocin-induced diabetic mice: the effect of insulin

Acetol and methylglyoxal are intermediates of the intrahepatic metabolism of acetone leading to pyruvate formation. In hepatocytes prepared from fasted streptozotocin-induced diabetic mice, net glucose production could be measured from methylglyoxal but not from acetone or acetol. Insulin increased glucose formation from methylglyoxal in a concentration-dependent manner, whereas it was ineffective when pyruvate was used as substrate. Drug oxidation, as evidenced byp-aminophenol formation from aniline, was enhanced by methylglyoxal, and insulin proved to be stimulatory in this case as well. It is concluded that insulin might be involved in the regulation of glucose formation from methylglyoxal, but its mode of action is not yet clear.     

Differences in the numbers of fenestrae between the arterial and venous ends of capillaries in the adrenal cortex

Résumé Dans le cortex adrénal des souris les limbes des capillaries vieneux ont 4.3 fenestrae endothéliales de plus que les limbes artériels. On estime que cette pré-pondérance des fenestraes vieneuses, qui se retrouve ailleurs, et très importante et permet à celles-ci d'enlever du tissu les grandes molécules extravasculaires.