Peri- and postnatal changes in reduced nicotinamide adenine dinucleotide phosphate-cytochrome P-450 reductase content in hepatocytes of rats

Summary To study the process of the expression of reduced nicotinamide adenine dinucleotide phosphate-cytochrome P-450 reductase (EC 1.6.2.4) in the liver during development, the amount of enzyme in the cytoplasm of periportal and perivenular hepatocytes in sections cut from livers of male rats was measured during peri- and postnatal growth by quantitative immunohistochemistry with a video image processor. In livers of 19-day-old foetuses, the reductase content in the cytoplasm of periportal and perivenular hepatocytes was 0.16 μM and 0.20 μM, respectively. From the 19th day of gestation to 5 days after birth, the enzyme content increased markedly in the cytoplasm of periportal (288%) and perivenular hepatocytes (301%). Subsequently, the content in the cytoplasm of periportal hepatocytes increased slightly (46%) from 5 to 20 days of age, remained unchanged from 20 to 45 days of age, and increased slightly (15%) from 45 to 90 days of age. However, the content in the cytoplasm of perivenular hepatocytes increased progressively (125%) between 5 and 90 days of age. Thus, the amount of cytochrome P-450 reductase increases markedly in periportal and perivenular hepatocytes during the perinatal period, and subsequently the enzyme content increases gradually in periportal hepatocytes and progressively in perivenular hepatocytes. The present results also suggest that the divergence between cytochrome P-450 expression and the cytochrome P-450-dependent drug metabolic activity in hepatocytes during the perinatal period, found in previous studies, can be attributed to a low cytochrome P-450 reductase density in the membrane of endoplasmic reticulum of periportal and perivenular hepatocytes.     

Intralobular distribution of UDP-glucuronosyltransferase in livers from untreated, 3-methylcholanthrene- and phenobarbital-treated rats

A 3-methylcholanthrene-inducible enzyme form of UDP-glucuronosyltransferase has been localized within the liver lobule both immunohistochemically and enzymatically in microdissected centrilobular and periportal liver tissue. Livers of untreated, 3-methylcholanthrene- and phenobarbital-treated rats have been compared. The enzyme was detected in hepatocytes throughout the liver. However both immunohistochemical determination of the enzyme level and biochemical determination of its activity towards 1-naphthol revealed a heterogeneous distribution of the enzyme. In untreated controls and 3-methylcholanthrene-treated rats both enzyme activity and histochemical staining was highest in centrilobular hepatocytes. However, after phenobarbital-treatment enzyme staining and activity was highest in periportal hepatocytes, suggesting that the differentially inducible enzyme activities may be localized in different zones of the liver lobule. The results demonstrate that the 3-methylcholanthrene-inducible UDP-glucuronosyltransferase is preferentially expressed in centrilobular hepatocytes.     

Quantitative analysis of development of mitochondrial ultrastructure in differentiating mouse hepatocytes during postnatal period

Between birth and 10 days of age, the volume density (volume/unit cytoplasmic volume) of the matrix, and the surface density (area/unit cytoplasmic volume) of the inner membrane and cristae increased in both periportal and perihepatic hepatocytes, and did not differ significantly between the cells of the two zones. After 10 days of age, however, the volume density of the matrix decreased in perihepatic cells and remained unchanged in periportal cells, and, therefore, it became greater in periportal cells than in perihepatic cells in 20-day-old and adult animals. The surface density of the inner membrane and cristae decreased in the cells of both zones. Further, the hepatocyte volume increased markedly, especially in perihepatic zones between 20 days of age and the adult. The results show that, in postnatally differentiating hepatocytes, mitochondria are likely to develop during early postnatal period, then the structural heterogeneity of mitochondria arises, and hepatocyte volume increases markedly during late postnatal period after weaning. Thus, the process of postnatal hepatocyte differentiation includes such several phases of development.     

Liver cell heterogeneity. The distribution of pyruvate kinase and phosphoenolpyruvate carboxykinase (GTP) in the liver lobule of fed and starved rats.

Pyruvate kinase and phosphoenolpyruvate carboxykinase activities were determined in microdissected freeze-dried liver cells from the periportal and pericentral area of the liver lobule. Pyruvate kinase activity was measured by a microfluorimetric procedure adapted to 20-200 ng tissue dry weight. In livers from fed rats, its activity was twice as high in the central zone as in the periportal cells; starvation reduced this gradient by decreasing central activities. Phosphoenolpyruvate carboxykinase activity was measured by a microradiochemical technique in 100-300 ng tissue dry weight. In livers from fed rats, this enzyme was nearly 3 times more active in the periportal cells than in the central area. Starvation increased this enzyme in both zones with a more pronounced change in the central cells. The results indicate a heterogeneous distribution of enzymes of carbohydrate metabolism in the liver lobule. Gluconegenesis seems to be localized preferentially in periportal hepatocytes, whereas the glycolytic enzyme was found to be more active in cells surrounding the pericentral liver cells.     

Immunohistochemical localization of β1-adrenergic receptors in the liver of male and female F344 rat

The distribution of beta(1)-adrenergic receptors in the liver of Fischer 344 (F344) rat has been examined by an immunohistochemical method. The study was carried out on formalin-fixed and paraffin-embedded livers from young adult, middle-aged, and old female and male F344 rats. An antibody specific for the beta(1)-adrenoreceptor subtype was used. A positive reaction was found in the liver parenchyma of female and male rats from all age groups. Within the liver lobule, a clear zonation is observed, with the beta(1)-adrenoreceptor positivity most evident in pericentral zone hepatocytes and a gradual fading of the immunostaining from pericentral to periportal zone hepatocytes, which may be completely negative. Immunoreactivity is localized on the cell membrane and on the membrane of peripheral cytoplasmic vesicles, and is mostly confined to the cell side facing vascular space. The intensity of immunostaining seems to be slightly higher in the 6- and 10-month-old female rats as compared to the matched male rats and to the senescent female rats. No age-related changes in the intensity of immunostaining are appreciable in male rats. However, no definite conclusion could be drawn about the existence of gender-related differences or age-related changes in the density of beta(1)-adrenoreceptors. A low density of beta1-adrenoreceptor was observed in the spontaneous preneoplastic lesions of the livers from senescent rats.     

Histochemical demonstration of guanase in human liver with guanine in bicine buffer as substrate

Summary Histochemical studies of human guanase (guanine deaminase) have seldom been undertaken, in part because of technical difficulties which result in heavy background staining. In this report, we describe a modified procedure in which the methodological inadequacies have been overcome. The modified technique has been applied to determine the intracellular and lobular distribution of guanase in normal human liver and in cases of primary biliary cirrhosis and alcoholic cirrhosis.Guanase was present within the cytoplasm of hepatocytes throughout the entire lobule. Enzyme activity was stronger on the sinusoidal side of the hepatocytes and in the periportal area. The reaction was weaker in perivenular hepatocytes. Portal components (bile ducts and veins), fibrous tissue and inflammatory cells were non-reactive, and the enzyme was absent from hepatocyte nuclei and membranes. Sections of skeletal muscle contained no guanase. The specificity of the reaction was confirmed by control tests on liver tissue and by the use of a specific inhibitor of guanase.It is concluded that the modified procedure overcomes the disadvantages inherent in the original method for guanase demonstration, allows the examination of fine cellular detail and should become a valuable histochemical tool with which to study diseases of the liver.     

Intralobular heterogeneity of perisinusoidal stellate cells in porcine liver

The aim of the present investigation was to elucidate the intralobular heterogeneity of the perisinusoidal stellate cells (fat-storing cells, lipocytes) in the porcine liver. Their three-dimensional structure, desmin immunoreactivity and vitamin-A storage were studied by use of the Golgi silver, immunocytochemical and gold chloride methods. In order to locate the stellate cells, the hepatic lobules were divided into 10 zones. The stellate cells were readily identified in Golgi preparations by their striking dendritic appearance with branching processes encompassing the sinusoids. The stellate cells in the centrolobular zones were conspicuously dendritic with longer processes in conspicuously dendritic with longer processes in comparison to those emitted by periportal elements. Such arborizations were studded with numerous thorn-like microprojections. Desmin immunoreaction in the periportal zones was stronger than that in the centrolobular zones. Vitamin-A storage in the stellate cells was well developed in zones 2–4, but reduced gradually toward the central region. The perisinusoidal etellate cells display marked heterogeneity in morphology and function based on their zonal location in the hepatic lobule.     

Heterogeneous distribution of glutamine synthetase during rat liver development

Two days before birth, immunohistochemical detection of glutamine synthetase already reveals a heterogeneous distribution pattern related to the vascular architecture of the liver. Only a small number of hepatocytes in the vicinity of the efferent venules show relatively high staining intensity. Before that age, only megakaryocytes show intense staining, while liver parenchyma is only faintly stained. The developmental profile of glutamine synthetase activity shows two periods of increasing enzyme activity: one in the perinatal period and one in the second and third postnatal week. Both periods are correlated with high levels of circulating corticosteroid hormones. Although the relative number of intensely stained hepatocytes increases during the first rise in enzyme activity, the second rise is correlated with a decreasing number of glutamine synthetase-positive hepatocytes which, however, show a considerable increase in staining intensity. Carbamoylphosphate synthetase shows a homogeneous distribution pattern in the perinatal period. Conditions that lead during development to a relatively high level of glutamine synthetase expression in the pericentral compartment apparently originate before the appearance of conditions that lead to a relatively high level of carbamoylphosphate synthetase gene expression in the periportal compartment. Our results indicate that downstream localization of glutamine synthetase in liver acinus is essential from the perinatal period onwards, whereas reciprocal distribution of glutamine synthetase and carbamoylphosphate synthetase gene expression (that is found in adult rat liver) is not.     

Immunofluorescence-microscopic localization of collagen type IV and VI, laminin and nidogen in the livers of Callithrix jacchus during pre- and postnatal development

The distribution of collagen type IV and VI, laminin and nidogen was investigated by immunofluorescence microscopy in the livers of marmosets (Callithrix jacchus) at various stages of development, i.e. on days 93, 111, 116 and 134 of gestation, 1 day postpartum and at the mature stage. Large amounts of collagen type IV could in all cases be demonstrated in the sinus wall and in all basal laminae outside the lobule. After the application of antibodies against collagen type VI the sinus wall showed a weak fluorescence reaction at the early stages and a strong binding towards the end of gestation which persisted up to the adult stage. In the periportal field it was mainly localized at the border between lobule and connective tissue. Laminin also increased gradually but could be demonstrated only until birth. In contrast, nidogen was present during the total prenatal and postnatal period. Therefore, collagen type IV and VI were not very suitable for the demonstration of an increase in matrix components under pathological conditions, because they occur already in large amounts in normal livers. However, the occurrence of laminin that was missing in the adult liver must be interpreted as pathological indication. The different occurrence of laminin and nidogen showed that these two substances were expressed and regulated independently of each other.     

In situ kinetic parameters of glucose-6-phosphatase in the rat liver lobulus.

Glucose-6-phosphatase activity has been determined in periportal and pericentral zones of the rat liver lobule using a quantitative histochemical method. The study was performed on unfixed cryostat sections of livers from fasted and fed female and male rats. Highest activity was found in periportal zones, and starvation caused a 2-3-fold increase of glucose-6-phosphatase activity in periportal and pericentral zones of both sexes. Unexpectedly, KM values were also significantly different in periportal and pericentral zones and were found to increase linearly with Vmax values, irrespective of sex and feeding condition. Because the cryofixation procedure was shown to permeabilize the biomembranes in the tissue sections, it can be concluded that the rise in KM and Vmax values has to be attributed to the catalytic unit of the glucose-6-phosphatase system. It is suggested that the enzyme exists in a high affinity configuration at low enzyme concentrations but that at high enzyme concentrations a hysteretic mechanism, as proposed by Berteloot et al. (Berteloot, A., Vidal, H., and Van de Werve, G. (1991) J. Biol. Chem. 266, 5497-5507), transforms the enzyme from a high to a low affinity configuration. The present study indicates that the concept of functional heterogeneity of liver parenchyma may be more complex than thus far assumed.     

Expression and regulation of glycogen phosphorylase in preneoplastic and neoplastic hepatic lesions in rats

Glycogen phosphorylase (PHO) was demonstrated immunocytochemically and enzyme histochemically in cryostat sections of liver from rats treated for 7 weeks with N-nitrosomorpholine (120 mg/l and 200 mg/l drinking water) and from untreated controls. The activity and distribution of PHO protein were studied in normal liver and correlated with morphologically defined stages of hepatic tumour development. In normal liver the amount of enzyme protein, as visualized by the immunoperoxidase method using antibodies against phosphorylase, showed some heterogeneity within the liver lobule. The intralobular and intracellular distribution of PHO protein was the same as that of glycogen, namely coarse and granular in periportal hepatocytes and very fine in perivenular cells. In glycogen storage foci the amount of PHO protein was increased. In contrast, PHO activity was generally decreased. In other preneoplastic and neoplastic lesions such as mixed cell foci, neoplastic nodules and hepatocellular carcinomas, PHO protein was increased in all glycogen-loaded cells while PHO activity was reduced. In all glycogen-poor and basophilic cells, both PHO protein and PHO activity were decreased or absent. It was concluded that the decrease in PHO activity in glycogen storage foci was not the direct consequence of genetic changes leading to a loss in enzyme protein but was due to a defect in the cascade of phosphorylation processes resulting in active PHO. Alteration in gene expression leading to a loss of PHO protein was a late event in the process of hepatocarcinogenesis.     

Microsomal electron-transport reductase activities and fatty acid elongation in rat brain. Developmental changes, regional distribution and comparison with liver activity.

Gestational and postnatal changes of microsomal NADH:cytochrome b5 reductase and NADPH:cytochrome c reductase activities were examined in rat brain. The specific activity of NADH:cytochrome b5 reductase was high at 18-19 days of gestational age, decreased to a minimum at 4 to 6 days after birth and increased thereafter. An essentially similar developmental pattern was observed for the specific activity of NADPH:cytochrome c reductase. In contrast, the specific activities of these reductases in liver microsomes were low, did not display a peak during gestation and increased steadily to a maximum at 40-50 days after birth. The rate of incorporation of [2-14C]malonyl-CoA into palmitoyl-CoA in brain microsomes was found to be high in the foetus, sharply decreased to a minimum at the time of birth and increased thereafter. The activity of fatty acid elongation in liver microsomes was much less than that in brain during gestation and increased rapidly after birth to values at 50-60 days 20-fold greater than the foetal activity. NADH and NADPH were equally effective for brain microsomal fatty acid elongation. Regional distribution of cytochrome reductase activities and the activity of fatty acid elongation showed the lowest specific activity in cerebellum. These results suggest that brain microsomal electron transport may be correlated with the developmental alteration in fatty acid elongation.     

Immunohistochemical localization of NADPH-cytochrome c reductase in rat liver.

NADPH-cytochrome $\text{c}$ reductase (NADPH-cytochrome reductase, EC 1.6.2.4), the flavoprotein which is responsible for the NADPH-dependent reduction of cytochromes P-450 in hepatic microsomes, has been localized immunohistochemically at the light microscopic level in rat liver. Localization was achieved through the use of sheep antiserum to rat hepatic microsomal NADPH-cytochrome $\text{c}$ reductase in an unlabeled antibody peroxidase-antiperoxidase technique. Parenchymal cells throughout the liver lobule were found to be stained positively for NADPH-cytochrome $\text{c}$ reductase, although the intensity of immunostaining was slightly greater in the centrilobular regions. Immunostaining for NADPH-cytochrome $\text{c}$ reductase was not detected in Kupffer cells, connective tissue cells, or in cells of the hepatic vasculature.     

A new microphotometric method for measurement of cytochrome P-450 in sections of liver

We developed a new microphotometric method for measuring the amounts of cytochrome P-450 (P-450) in fresh frozen sections of liver. Four serial frozen sections cut from the liver were separately incubated in 50 mM Tris-HCl buffer (pH 8.0) alone, in buffer containing sodium dithionite, in buffer saturated with carbon monoxide (CO), and in buffer saturated with CO and containing sodium dithionite. The difference between absorbance at 450 nm and that at 490 nm was measured in these sections with a simple microphotometer system. This method yielded precise amounts of P-450 in sections by measuring the true extinction of P-450 and by minimizing the effect of contaminating hemoproteins. Livers of adult rats contained large amounts of P-450, which was greater in perivenular hepatocytes than in periportal hepatocytes. In livers of newborn rats, however, small amounts of the enzyme were distributed evenly throughout the lobule.     

Functional heterogeneity of rat hepatocytes: predominance of aryl hydrocarbon hydroxylase activity in perivenular zone

To elucidate the hepatic intralobular distribution of aryl hydrocarbon hydroxylase (AHH) activity biochemically, periportal (PP) and perivenular hepatocytes (PV) from male Sprague-Dawley rats were separated by a fluorescence-activated cell sorter after labeling the PP zone with fluorescein diacetate and the perivenular zone with fluorescein isothiocyanate. AHH activity was higher in PV than in PP. The enzyme activity was induced about 6-fold in hepatocytes of rats pretreated with 3-methyl-cholanthrene, and the induction was more prominent in PP than in PV. Neither phenobarbital pretreatment nor altered lipid content of the diet induced the change in the enzyme activity.     

Growth,mitosis and morphogenesis of the simple liver acinus in neonatal rats

Radioautography after ³H-thymidine injection, blockage of mitosis due to colchicine and camera lucida drawings were used to study growth, mitosis and morphogenesis in the simple liver acinus of Rappaport in neonatal rats. Hepatic parenchymal cell plates are irregularly arranged and thick from birth to 4 days postpartum. By 10 days the plates begin to assume the adult configuration, irregular and thick in acinar zone 1 (periportal) but straight and thin in acinar zone 3 (pericentral). After a single injection of ³H-thymidine at birth the distribution of labeled nuclei among the hepatic acinar zones was such that zone 1 contained most, zone 3 least, and zone 2 an intermediate amount. This relationship remained constant out to 10 days postpartum. The amount of labeled cells within each zone varied, reaching its highest values at 2 days in zones 1 and 2 but not until 4 days in zone 3. Similar to the distribution of labeled nuclei, frequency of mitosis also exhibited a constant relationship of zone 1 > zone 2 > zone 3, but peaks of cell division within each zone were not always present. All three zones displayed a peak of mitosis at 4 days, whereas a second mitotic peak at 10 days was attained only by cells in zones 1 and 2.Conclusions are: (1) The neonatal liver is an expanding cell population with most of the expansion confined to acinar zones 1 and 2, (2) the period of 4–6 days postpartum is critical and could be the time when acinar metabolic zones are forming, (3) the irregular arrangement of cell plates in the center of the acinus (zone 1) may act to dampen arterial pulsations and allow adequate mixing of arterial and venous blood, (4) immediate postnatal growth of the liver acinus, as shown by an increase in its width, is due primarily to an increase in cell number since individual cell size does not increase.     

Immunohistochemical localization of epoxide hydratase in rat liver

An antibody produced against epoxide hydratase (EC 4.2.1.63) which had been purified to apparent homogeneity from hepatic microsomes of phenobarbital pretreated rats was employed in an unlabeled antibody peroxidase-antiperoxidase technique to localize the enzyme at the light microscopic level in the livers of untreated rats. Immunohistochemical staining for epoxide hydratase was detected in parenchymal cells throughout the liver lobule. Cells within the centrilobular regions, however, were observed to be stained more intensely than were those within the midzonal and periportal regions of the lobule. The results of this immunohistochemical study thus demonstrate that epoxide hydratase does not exhibit a uniform pattern of distribution within the liver lobule in untreated rats.     

Gluconeogenesis predominates in periportal regions of the liver lobule

Rates of gluconeogenesis from lactate were calculated in periportal and pericentral regions of the liver lobule in perfused rat livers from increases in O2 uptake due to lactate. When lactate (0.1-2.0 mM) was infused into livers from fasted rats perfused in either anterograde or the retrograde direction, a good correlation (r = 0.97) between rates of glucose production and extra O2 uptake by the liver was observed as expected. Rates of oxygen uptake were determined subsequently in periportal and pericentral regions of the liver lobule by placing miniature oxygen electrodes on the liver surface and measuring the local change in oxygen concentration when the flow was stopped. Basal rates of oxygen uptake of 142 +/- 11 and 60 +/- 4 mumol X g-1 X h-1 were calculated for periportal and pericentral regions, respectively. Infusion of 2 mM lactate increased oxygen uptake by 71 mumol X g-1 X h-1 in periportal regions and by 29 mumol X g-1 X h-1 in pericentral areas of the liver lobule. Since the stoichiometry between glucose production and extra oxygen uptake is well-established, rates of glucose production in periportal and pericentral regions of the liver lobule were calculated from local changes in rates of oxygen uptake for the first time. Maximal rates of glucose production from lactate (2 mM) were 60 +/- 7 and 25 +/- 4 mumol X g-1 X h-1 in periportal and pericentral zones of the liver lobule, respectively. The lactate concentrations required for half-maximal glucose synthesis were similar (0.4-0.5 mM) in both regions of the liver lobule in the presence or absence of epinephrine (0.1 microM). In the presence of epinephrine, maximal rates of glucose production from lactate were 79 +/- 5 and 59 +/- 3 mumol X g-1 X h-1 in periportal and pericentral regions, respectively. Thus, gluconeogenesis from lactate predominates in periportal areas of the liver lobule during perfusion in the anterograde direction; however, the stimulation by added epinephrine was greatest in pericentral areas. Differences in local rates of glucose synthesis may be due to ATP availability, as a good correlation between basal rates of O2 uptake and rates of gluconeogenesis were observed in both regions of the liver lobule in the presence and absence of epinephrine. In marked contrast, when livers were perfused in the retrograde direction, glucose production was 28 +/- 5 mumol X g-1 X h-1 in periportal areas and 74 +/- 6 mumol X g-1 X h-1 in pericentral regions.(ABSTRACT TRUNCATED AT 400 WORDS)