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

To investigate the parenchymal units in the liver of the rat three-dimensionally, 15 micrometer cryosections were used for the demonstration of glucose-6-phosphatase (G6Pase) activity to visualize the borders of the individual units. Together with the supplying and draining vessels, they were traced through a sequence of 146 sections and reconstructed. A cone-shaped secondary unit with a height of 2.1 mm and a volume of 3.3 mm3 was reconstructed. It was "covered" by a continuous vascular surface, consisting of portal tracts and vascular septa, connecting the portal venular branches. The secondary unit was subdivided by portal tracts and vascular septa, and by branches of a draining central venular tree into 14 primary units. Most of them were tri- to heptahedral in shape. The height varied between 330 and 840 micrometer, and the volume varied between 0.094 and 0.621 mm3. The branches of the portal venular tree, with diameters from 28 +/- 5 micrometer to 61 +/- 14 micrometer, were oriented preferentially along the vertical axis of the units. Most of the primary units were drained by single branches of the central venular tree, located in the center and oriented along the vertical axis of the units. Vessel diameters ranged from 62 +/- 14 micrometer to 216 +/- 9 micrometer. The average length of the sinusoids was 355 +/- 3 micrometer. From the results of this reconstruction study, it was concluded that the concept of the liver acinus cannot be applied to the liver of the rat.

Purkinje cell lineage and the topographic organization of the cerebellar cortex: a view from X inactivation mosaics.

We utilized a strain of mice, derived from a radiation mutagenesis experiment and carrying an activity-attenuated allele of the X-linked enzyme glucose-6-phosphate dehydrogenase (G6PD), to analyze the development of the cell lineage leading to cerebellar Purkinje neurons. Due to random X inactivation during early embryonic development, X- linked genes can be used to distinguish between clonally related populations of cells in X inactivation mosaics. Following histochemical staining for G6PD activity, the numeric proportions of Purkinje cells expressing either the wild-type or the mutant enzyme and the spatial distribution of these cellular phenotypes and their relation to anatomically and genetically defined cerebellar compartments were analyzed. Our data suggest that cerebellar Purkinje neurons originate from a limited pool of some 129 precursors. The size of this pool is different from the one derived from chimeric mice, allowing us to deduce the relative timing of Purkinje cell lineage restriction. Our data also show that Purkinje neurons of distinct lineage are extensively intermingled within the cerebellar cortex. Together, these findings suggest both a role for cell-cell communication in the development of genetically defined cerebellar compartments and a temporal window during which such cellular interactions may take place.

Glucose levels and succinate and lactate dehydrogenase activity in EMT6/Ro tumor spheroids.

To evaluate the effects of glucose on the development of cell heterogeneity and the occurrence of necrotic areas in the center of tumor spheroids, a procedure (combining microdissection of small tissue samples from frozen-dried cryosections and microchemical analysis) was developed to measure glucose in distinct, concentrically arranged, microregions of tumor spheroids: the outermost area of proliferating cells, the area of nonproliferating cells and 2 central "necrotic" areas, with either abundant or little intercellular space. Since glucose levels, for analytical reasons, had to be expressed on a dry weight basis, and because of the morphological heterogeneity of the microregions of tumor spheroids, it was necessary to measure and take into account the regional differences in cell density (water content), in order to obtain adequate estimates of the glucose levels in the various microregions. At glucose concentrations of 5.5 and 3.6 mM in the culture medium, the glucose levels varied between 3.5 and 1.4 mmoles/kg wet weight and were lowest in those central areas where the cell density was lowest. Histochemical demonstration of the distribution of lactate and succinate dehydrogenase activity indicates a considerably higher capacity of tumor cells for anaerobic than for aerobic energy production.

Distribution of 3-hydroxybutyrate dehydrogenase in primary lobules of rat liver.

In an attempt to establish the functional organization of the hepatic parenchymal unit, we used histo- and microchemical procedures to assess metabolic liver cell heterogeneity at the level of the primary lobule. Because of the close interrelation of glucogenesis and ketone body formation, and in view of the distinct regional differences of the in vivo activity of glucose-6-phosphatase (G6Pase), these techniques were used on livers from male rats to investigate the distribution of the ketogenic enzyme, 3-hydroxybutyrate dehydrogenase (3-HBDH), during the post-resorptive phase. A close reciprocity was found between the general increase in the activity of 3-HBDH and the decrease of the in vivo activity of G6Pase along the sinusoidal axis, and also with regard to enzyme gradients along sinusoids of different origin. The activity of the ketogenic enzyme was higher throughout septal than portal sinusoids, whereas the opposite applied to the glucogenic enzyme. Histo- and microchemical data support the concept of a lobular parenchymal unit composed of "primary lobules," and show also that hepatocyte function varies with cell location along the sinusoidal axis and with the origin of the sinusoids.

Regionality of glucose-6-phosphate hydrolysis in the liver lobule of the rat: metabolic heterogeneity of "portal" and "septal" sinusoids.

To investigate intercellular compartmentation of liver metabolism, we have recently introduced new procedures for quantitative assessment of metabolic liver cell heterogeneity both along sinusoids of portal and septal origins as well as at the level of the parenchymal unit, and also for three-dimensional imaging of enzyme and metabolite distribution. As part of the evaluation of the role of metabolic liver cell heterogeneity for the regulation of net substrate flux in the glucose-6-phosphatase/glucokinase system, and for the reduction of of these antagonistic enzymes, these techniques were used on livers from male rats. They served to obtain distribution data on glucose-6-phosphatase (the hydrolytic component of the glucose-6-phosphatase/glucokinase system) and its substrate, glucose-6-P, during the postresorptive phase (i.e., a metabolic state of net glucose release). Glucose-6-phosphatase (Vmax) and glucose-6-P were shown to decrease along the sinusoidal axis, and values of both parameters were significantly higher along sinusoids of portal than septal origin. Distribution of in vivo rates of glucose-6-P hydrolysis indicates the importance of metabolite distribution for in vivo regulation of liver cell function, insofar as it considerably increases the degree of heterogeneity among hepatocytes over that maximal rates of glucose formation. Histo- and microchemical data support the concept of a "lobular parenchymal unit" composed of "primary lobules," and justify the conclusion that hepatocyte function, in addition to the hormonal and nutritional states of the animal, not only depends upon cell location along the sinusoidal axis, but also on the origin of sinusoids.

A new sample isolation procedure for microchemical analysis of functional liver cell heterogeneity.

In conjunction with the investigation of intercellular compartmentation of liver carbohydrate metabolism, a new procedure for isolation of tissue samples from freeze-dried cryosections was developed. It was designed to permit assessment of functional differences between sinusoids of portal and septal origin, and to extend investigation of liver cell heterogeneity along sinusoids to the level of the structural-functional unit. Application of this procedure, together with microchemical assays of high analytical sensitivity, enabled measurement of 50 individual glucose and glucose-6-P values in a single cross-sectional area of about 0.75 mm2 of a liver unit. Preliminary results on the distribution of glucose and glucose-6-P indicated that, in a state of overall glucose release glucose levels were significantly higher in the center than in the periphery of the unit. Overall glucose release by the liver resulted from both release and uptake of glucose along sinusoids. Glucose-6-P was highest in the periphery and decreased toward the center. Microchemical data, furthermore, indicated possible functional heterogeneity of sinusoids, insofar as both glucose and glucose-6-P gradients were steeper in "portal-central" than in "septal-central" sinusoids.

Use of 3-D-computer graphics for imaging of distribution of hepatic metabolites.

In conjunction with the investigation of intercellular compartmentation of liver metabolism and as a logical further step, following the introduction of a new sample isolation procedure for microchemical analysis of functional liver cell heterogeneity, the possible benefit of computer-assisted three-dimensional imaging procedures for the reconstruction of hepatic metabolite distribution was investigated. In this intent, we elected to access a central computer facility by means of a small microcomputer system which, nevertheless, permitted to take full advantage of a large capacity main-frame computer and a high quality graphics plotter, at comparatively low overall costs. Commercially available software (SAS/GRAPH) was tailored to the specific requirements of this application. The three-dimensional imaging process recombines microchemical data (metabolite or enzyme values) with those of the size and location of samples within a particular cross-sectional area of a liver unit and provides an integrated view of metabolite distributions. The three-dimensional images were then used to define general distribution characteristics, as well as, differences in metabolite distribution along sinusoids of portal and septal origin. Glucose increased, whereas glucose-6-P decreased along sinusoids from the beginning to the end and values of both metabolites were found to be higher along 'portal/central' than along 'septal/central' sinusoids. Co-distribution of glucose-6-phosphatase with its substrate (glucose-6-P) was indicated by histochemical and microchemical results and is anticipated to be of considerable regulatory importance, since it further enhances the differences among hepatocytes at different locations along sinusoids with respect to their ability to produce glucose.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative histochemical assessment of regional differences in hepatic glucose uptake and release.

As a further step in the investigation of the heterogeneity of liver cells in general and regionality of glucose metabolism in particular, requirements for isolation of appropriate tissue samples were defined and procedures for measurement of the biochemical parameters responsible for glucose uptake and release developed and tested. By using enzymatic cycling for chemical amplification, in conjunction with the oil-well technique, sufficient analytical sensitivity was provided to assay samples averaging 20 ng dry weight. Microchemical data on the distribution of glucokinase and glucose-6-phosphatase and of their substrates, glucose and glucose-6-P, were used to, first calculate in vivo rates of these catalytic steps by means of the Michaelis-Menten equation, and then, to determine the direction and rate of net glucose flux, as well as, the rate of substrate cycling between glucose and glucose-6-P. Calculations from the results indicated a reciprocal distribution of in vivo glucokinase and glucose-6-phosphatase velocities, as well as, sex-specific differences. The distribution of in vivo activities results in a spatial separation of these antagonistic steps. Separation is incomplete, but nevertheless appears to lead to regionally different rates in futile substrate cycling. Glucose gradients permit differentiation between net glucose uptake and release and were, therefore, used as a test of the validity of the calculations of in vivo activities. The observed discrepancies between glucose gradients and calculated in vivo enzyme activities illustrate the power of this approach: it provides a way to compare changes in glucose along the sinusoid with what would be predicted from the levels of enzymes which liberate and tie up glucose and of their respective substrates.

Sex-specific regionality of liver metabolism during starvation; with special reference to the heterogeneity of the lobular periphery.

Staining procedures for glucose-6-phosphatase and 3-hydroxybutyrate dehydrogenase activity and for glycogen were used to investigate adaptive changes in the regionality of hepatic gluconeogenesis and ketogenesis in fasting male and female rats. A reciprocal distribution of gluconeogenic and ketogenic capacities was found in both sexes, but male and female animals were different with respect to: a) the time necessary for full induction of glucose-6-phosphatase activity (24 h in females, 48 h in males); b) the overall activity of 3-hydroxybutyrate dehydrogenase; and c) glycogen content. The activity of the latter enzyme and the glycogen content did increase with time of starvation, but at all times, were higher in males, than in females. Results, thus, indicate that the extent to which ketone bodies replace glucose as major fuel for the brain is larger in males than in females. This may explain the delayed induction of glucose-6-phosphatase activity and the higher glycogen content in the male during starvation. Distributions of enzyme activities and of glycogen, furthermore, revealed the heterogeneity of the lobular periphery, i.e. functional differences among sinusoids dependent upon whether they originate from the portal tract or the vascular septum, and thus confirm the lobular concept proposed by Matsumoto et al. (1979).

Metabolic zonation in thioacetamide-induced liver cirrhosis.

After TAA administration to rats a central part may be distinguished histochemically from a marginal part in most of the cirrhotic nodules. The centre is characterized by a high glycogen content and by high activity of phosphorylase, G6Pase and SDH; the maxima of which are situated around the larger blood vessels. The vasculatory periphery, however, shows moderate G6PDH-activity. The marginal parts of the nodules are poor in glycogen and possess only weak G6Pase and phosphorylase activity, whereas high SDH- and G6PDH-activity can be demonstrated here. This distribution pattern leads to the conclusion that the larger blood vessels in the centre of the nodules are themselves the terminal afferent vessels. Thus the centre of the nodule corresponds to periportal zone 1, while G6PDH-activity marks the area corresponding to zone 3. The fact that the marginal parts of the nodules are marked by high SDH- but weak G6Pase-activity is interpreted as the result of a preferential arterial supply to this parenchymal part. The high G6PDH-activity of the marginal part is seen in context with the regeneration processes. In all animals single nodules could be found with a high glycogen content and extremely high G6PDH-activity. This loss of heterogeneity is interpreted as a first step in the direction of malignancy.

High activity of glucose-6-phosphate dehydrogenase in Kupffer cells isolated from rat liver.

Sinusoidal cells in the rat liver react intensively for G6DPH activity after appropriate incubation (Rieder et al. 1978). After isolation and purification of the sinusoidal Kupffer and endothelial cells, it was demonstrated that Kupffer cells exhibit a 5-8 times higher G6PDH activity on a per cell basis by comparison with endothelial cells, while the specific G6PDH activity was 3-4 times higher in Kupffer cells. The Kupffer cells can be divided into two groups which differ significantly in G6PDH activity calculated on a per cell basis. In histochemical studies, G6PDH can be used as a marker for Kupffer cell identification.

The development of functional heterogeneity in the liver parenchyma of the golden hamster.

Prenatal and postnatal stages of the development of golden hamsters were studied histochemically and biochemically. It was shown that, beginning with the 12th gestational day, the fetal liver starts to store glycogen, and that this process reaches its maximum a birth. Glycogen phosphorylase and glucose-6-phosphatase (G6Pase)-activity increased drastically in the last two days before birth, glycogen phosphorylase preceding G6Pase. As a histochemical characteristic, an even distribution of glycogen, glycogen phosphorylase and G6Pase activity is found in the liver parenchyma at birth. During the first two postnatal weeks typical heterogeneous patterns of distribution developed: glycogen depletion could be demonstrated predominantly in zone 1 of the liver acinus, this being at the same time the area of highest glycogen phosphorylase and G6Pase-activity. The periportal zone 1 thus became characterized as the primary site of glycogenolysis (glycogen phosphorylase) and gluco(neo)genesis (G6Pase). "Metabolic Zonation" is interpreted as the chemomorphological equivalent of the regulatory function of the liver as a glucostat.

Histochemical studies on carbohydrate metabolism in rat liver after galactosamine administration.

The development of hepatitis, induced in 48 rats by the administration of galactosamine (GalN) in varying doses, was studied with the use of substrate and enzyme histochemical techniques. The so-called atypical glycogen, which is at first highly resistant to diastase, was shown to be digestible after deamination. The increasing accumulation of atypical glycogen during the course of GalN-hepatitis conceals the loss of normal glycogen when the PAS-reaction is used. Nevertheless glycogenolysis could also be demonstrated by the increasing activity of phosphorylase. The acid phosphatase activity was progressively diminished, which was interpreted as signifying early lysosomal damage. G6Pase activity remained nearly constant but SDH showed a decrease in activity after 12 h. These histochemical results are considered to provide deeper insight into the pathological mechanism of GalN-hepatitis.

NADP-dependent dehydrogenases in rat liver parenchyma. II. Comparison of qualitative and quantitative G6PDH distribution patterns with particular reference to sex differences.

Qualitative histochemical G6PDH distribution patterns obtained in the liver acinus of adult male and female rats with an improved method (Rieder et al., 1978) served as a basis for the isolation by microdissection of tissue samples of defined zonal affiliation. G6PDH activity was assayed quantitatively in tissue samples of zones 1 and 3 by a microfluorometric method, using the oil well technique and enzymatic cycling (Burch et al., 1963; Lowry and Passonneau, 1972). With the use of a correlation system further evidence could be presented for the validity of the recently described qualitative distribution patterns. From a total of 50 analyzed tissue samples the following G6PDH activities were calculated: 4.25 +/- 1.56 U/g dry weight in zone 1 and 2.08 +/- 0.46 U/g dry weight in zone 3 of male and 7.21 +/- 1.03 U/g dry weight in zone 1 and 11.10 +/- 2.56 U/g dry weight in zone 3 of female rats. These data were corrected for interference from the G6PDH activity of the Kupffer cells within zone 1 samples (approximately 80 U/g dry weight), so that the actual relative values for the parenchymal activity could be estimated for the first time: 2 U/g dry weight in zones 1 and 3 of male animals, 5 U/g dry weight in zone 1 and 11 U/g dry weight in zone 3 of female animals. In female livers G6PDH activity in zone 1 is therefore 2.5 times higher, and in zone 3 5 times higher than in the male. These zonal as well as sex-differences are clearly indicative of a heterogeneous functional organization of the liver acinus in terms of capacity for NADPH production, mainly in connection with reductive reactions in fatty acid synthesis.

Identification of G6PDH-active sinusoidal cells as Kupffer cells in the rat liver.

The aim of this study was to identify the G6PDH-active sinusoidal cells in the rat liver described by Rieder et al. (1978). Because of their number and distribution in the liver parenchyma, endothelial cells and pit cells could be excluded. Fat-storing cells were specifically marked by vital staining with vitamin A and identified by fluorescence microscopy. Kupffer cells could be detected after vital staining with carmine. Both staining methods allowed a subsequent incubation for the demonstration of G6PDH activity in the same unfixed cryostat section. Whereas more than 80% of the fluorescent particles were found outside the enzyme-positive cells, all G6PDH-active cells contained carmine particles. After counting the G6PDH-active cells, an estimation of 0.217 x 10(8) cells/g liver tissue was obtained. The results indicate that high G6PDH activity is common to all Kupffer cells, and is therefore a highly specific marker enzyme for this class of sinusoidal liver cells.

Quantitative determination of G6Pase activity in histochemically defined zones of the liver acinus.

Qualitative histochemical G6Pase distribution patterns obtained with an improved method (Teutsch, 1978) served as the basis for a zonal microdissection of the liver acinus. G6Pase activity was determined quantitatively in tissue samples of zones 1 and 3 by a microfluorometric method (Burch et al., 1978). Using a correlation system it could be demonstrated that the histochemical distribution pattern obtained with the improved method was in better agreement with quantitatively estimated zonal differences of G6Pase activity, both in fed and starved female rats, than with the Wachstein and Meisel medium (1956). From a total of 50 tissue samples analyzed the following average G6Pase activities were calculated: in fed animals 15.36 +/- 3.48 U/g dry weight in zone 1, and 9.28 +/- 2.15 U/g dry weight in zone 3; in starved female rats 42.50 +/- 8.20 U/g dry weight in zone 1, and 29.25 +/- 5.68 U/g dry weight in zone 3. The qualitative histochemical as well as quantitative zonal differences of G6Pase activities are taken as further support for the hypothesis of metabolic zonation of liver parenchyma.