Three-dimensional reconstruction of parenchymal units in the liver of the rat

Intracellular localization of constitutive and inducible heat shock protein 70 in rat liver after in vivo heat stress

The level and intracellular redistribution of the two nucleo-cytoplasmic members of 70 kDa heat shock protein family (constitutive, Hsc70 or Hsp73, and inducible, Hsp72) were studied in rat liver during a 24-h period after exposure of the animals to 41 degrees C whole body hyperthermic stress. The examined proteins were detected in the liver cytosol and nuclei by Western blotting and immunohistochemical staining of paraffin sections, as well as by immnocytochemical staining of isolated nuclear smears. All three techniques applied were based on the use of monoclonal antibodies recognizing both constitutive and inducible Hsp70 isoforms or only the inducible isoform, and gave consistent results. The exposure of the animals to in vivo heat stress was shown to induce the synthesis of otherwise non-existing Hsp72, rendering Hsc70 level unchanged in comparison to unstressed controls. However, immediately after the stress the intracellular redistribution of Hsc70, i.e. its nuclear accumulation, was observed. The maximal level of Hsp70 both in the cytoplasm and in the nuclei was registered 5 h after the stress, which coincided with the maximal level of Hsp72 induction. The alterations in the level and intracellular distribution of examined proteins were still noticeable 24 h after the stress. The results of this study could shed some more light on, as yet uncertain, differences between cellular functions of these two proteins, as well as on the role of the constitutive form under normal and stress conditions.

In vivo and ex vivo virtual biopsy of the liver with near-infrared, reflectance confocal microscopy

The assessment of liver architecture is an essential part of the understanding of its physiology and pathology. Current fluorescence confocal microscopy methods face numerous drawbacks, such as cytotoxicity, quenching effect, potential negative ino- and chrono-tropic effects and leaking of fluorescent agents through the sinusoid fenestrations. The recently developed, near-infrared reflectance confocal microscopy allows high-resolution optical sectioning through intact tissues, without employing fluorescent stains, while contrast between structures is provided by the natural refractivity of the tissue. The aim of this study is to assess the utility of near-infrared reflectance confocal microscopy in the evaluation of the hepatic microscopic architecture in vivo and ex vivo. Rat livers were noninvasively examined in vivo and ex vivo with near-infrared reflectance confocal microscopy. Two experimental contrast agents were subsequently used to enhance particular structures. Parenchymal and vascular structures are readily identified, as well as some intracellular details. Differences between in vivo and ex vivo states were also observed. The use of contrast agents also highlights certain morphologic structures. In conclusion, near-infrared reflectance confocal microscopy stands as a useful adjunct technique to the study of hepatic parenchyma offering details equivalent to, if not surpassing traditional light microscopy.

Stereological measurement of porto-central gradients in gene expression in mouse liver

The liver is thought to consist of lobules, numerous repeating, randomly oriented units. Within these lobules, genes are expressed in gradients along the porto-central axis, which spans the distance between portal and central veins. We have developed a robust stereological method to map all points in an image to their position on this porto-central axis. This approach is based on the distribution of well-characterized periportal and pericentral enzymes, which are visualized on sections preceding and following the section of interest. Because expression of the model genes phosphoenolpyruvate carboxykinase and ornithine aminotransferase declines gradually with increasing distance from the portal vein and central vein, respectively, these genes can be used to prepare images with topographical information without any assumption about the shape of the hepatic unit, or about the direction or shape of the gradient to be determined. The "relative distance" image is a 2-dimensional image that accurately maps the relative position of hepatocytes on the porto-central axis in 3-dimensional space. It is superimposed on the serial section under investigation to relate local staining density to position on the porto-central axis and obtain the gene expression gradient. The method was used to determine the expression gradient of 2 periportal and 2 pericentral enzymes and their response to fasting. The "total distance" image was used to measure the length of the porto-central axis, which was approximately 210 microm in mice and found to decrease 13% after 1 day of starvation. The method can be applied to any tissue component that can be stained quantitatively.

Acute inhibition of glucose-6-phosphate translocator activity leads to increased de novo lipogenesis and development of hepatic steatosis without affecting VLDL production in rats

Glucose-6-phosphatase (G6Pase) is a key enzyme in hepatic glucose metabolism. Altered G6Pase activity in glycogen storage disease and diabetic states is associated with disturbances in lipid metabolism. We studied the effects of acute inhibition of G6Pase activity on hepatic lipid metabolism in nonanesthetized rats. Rats were infused with an inhibitor of the glucose-6-phosphate (G6P) translocator (S4048, 30 mg. kg(-1). h(-1)) for 8 h. Simultaneously, [1-(13)C]acetate was administered for determination of de novo lipogenesis and fractional cholesterol synthesis rates by mass isotopomer distribution analysis. In a separate group of rats, Triton WR 1339 was injected for determination of hepatic VLDL-triglyceride production. S4048 infusion significantly decreased plasma glucose (-11%) and insulin (-48%) levels and increased hepatic G6P (201%) and glycogen (182%) contents. Hepatic triglyceride contents increased from 5.8 +/- 1.4 micromol/g liver in controls to 20.6 +/- 5.5 micromol/g liver in S4048-treated animals. De novo lipogenesis was increased >10-fold in S4048-treated rats, without changes in cholesterol synthesis rates. Hepatic mRNA levels of acetyl-CoA carboxylase and fatty acid synthase were markedly induced. Plasma triglyceride levels increased fourfold, but no differences in plasma cholesterol levels were seen. Surprisingly, hepatic VLDL-triglyceride secretion was not increased in S4048-treated rats. These studies demonstrate that inhibition of the G6Pase system leads to acute stimulation of fat synthesis and development of hepatic steatosis, without affecting hepatic cholesterol synthesis and VLDL secretion. The results emphasize the strong interactions that exist between hepatic carbohydrate and fat metabolism.

Validation of confocal laser scanning microscopy for detecting intracellular calcium heterogeneity in liver slices

To investigate changes in the intracellular Ca(2+) ([Ca(2+)]i) in liver lobules under aerobic and hypoxic conditions, we measured [Ca(2+)]i in liver slices using a confocal laser scanning microscope (CLSM). The liver lobule is divided into 3 equal parts between the central vein and portal area, Zones 1, 2, and 3 from the portal side. [Ca(2+)]i in each zone of cultured rat liver lobules was measured by CLSM and a fluorescent Ca(2+) indicator (Rhod 2 AM). After the culture solution was changed to an Na(+)-free solution under aerobic conditions, the percentage of cells showing an increase in [Ca(2+)]i was 66.0+/-9.7% in Zone 1, 70.0+/-10.5% in Zone 2, and 94.0+/-9.7% in Zone 3. The percentage was significantly higher in Zone 3 than in Zones 1 and 2 (P< .01). Under hypoxic conditions, the percentage of cells showing an increase in [Ca(2+)]i was 6.0+/-9.7% in Zone 1, 8.0+/-10.3% in Zone 2, and 10.0+/-10.5% in Zone 3. There were no differences among the 3 zones. In all zones, the percentage was higher under aerobic conditions than under hypoxic conditions (P< .01). These results indicated that the increase in [Ca(2+)]i in liver lobules was heterogeneous. Measurement of [Ca(2+)]i in liver slices by CLSM was considered useful for studying heterogeneity between liver lobules, as well as between liver cells.

Three-dimensional observations of spatial arrangement of hepatic zonation and vein system in mice and house musk shrews

The three-dimensional (3D) relationship among the hepatic domains and the efferent central and afferent portal veins was investigated by macroscopy, microscopy, and computer-aided 3D reconstruction methods. To clearly distinguish the pericentral domain from the periportal, we used CCl(4)-treated mice and diabetic house musk shrews, which show typical pericentral necrosis and deposition of fat, respectively. The 3D findings obtained were verified against normal control animals using advantages of our unique observations by light and fluorescent microscopy, which made it possible to differentiate the two domains well. The pericentral domains in the mice and shrews appeared three-dimensionally as continuous branched columns, and the periportal domains exist in a sponge-like network that fills the parenchymal space among the columnar pericentral domains. The efferent central veins were concentrically surrounded by the pericentral domain, and segments of the central veins flowed into large sublobular and lobar veins. The walls of these large veins faced the pericentral domain at the confluence with the central veins; the remaining portions of the walls faced the periportal domain. The afferent portal veins were placed at the two-dimensional center of the network of the periportal domain and gave off smaller portal branches radially at the intersections of the network. Three types of liver lobules-classic, portal, and acinar-have been discussed repeatedly at the (2D) level. At the 3D level, it is reasonable to consider that the liver parenchyma consists of the two continuous domains corresponding to the distribution of the vessels that we found.

Lobular distribution pattern of lactate dehydrogenase and 6-phosphogluconate dehydrogenase activity in rat liver

Lactate dehydrogenase (LDH) and 6-phosphogluconate dehydrogenase (6-PGDH) activities were measured in lobular areas expanding between 3 portal tracts and an efferent central vein in the livers of male Wistar rats, using a Lowry technique. The maximum of LDH activity was found in a nearly uniform broad area in the lobular periphery. From that area values decreased along periportal/septal-->perivenous gradients, but only slightly within that area along the periportal-->septal axis of the vascular septum. Maximum values of 6-PGDH activity were present in an intermediate area close to the central vein demonstrating a rather inhomogeneous distribution pattern without a clear definition of zonal limits. Our data on the distribution pattern of LDH are in agreement with the concept of the metabolic lobulus and are supported by a recent evaluation of the vascular architecture in rat liver. The lobular distribution pattern of 6-PGDH cannot be interpreted without doubt in accordance with that concept.

Expression pattern of glutamine synthetase marks transition from collecting into conducting hepatic veins

The expression of glutamine synthetase (GS) is confined to a rim of hepatocytes surrounding the efferent hepatic veins in all mammalian species investigated. In rat liver, a two- to three-cell thick layer of GS-positive (GS(+)) hepatocytes uniformly surrounds the two to four terminal branching generations of the hepatic vein that collect blood from sinusoids (central veins). With increasing diameter of the efferent vessel, this multilayered rim of GS(+) hepatocytes becomes confined to patches surrounding the decreasing number of central vein outlets. The remaining part of the wall of these sublobar hepatic veins is bordered by a one-cell thick layer of GS(+) hepatocytes. Around still larger veins, this single-cell layer of GS(+) hepatocytes gradually disappears. The expression pattern of GS is therefore a convenient biological parameter to delimit sinusoidal draining ("collecting") from nondraining ("conducting") surfaces in the wall of the efferent hepatic vessels. The hepatocytes surrounding a single tree of central veins together form a compound liver lobule. (J Histochem Cytochem 47:1507-1511, 1999)