Alfa and beta estrogen receptors and the biliary tree.

This manuscript summarizes recent data showing that estrogens and their receptors play an important role in modulating cholangiocyte proliferation. We have recently demonstrated that rat cholangiocytes express both estrogen receptors (ER)-alpha and -beta subtypes, while hepatocytes only express ER-alpha. ER and especially the ER-beta subtype, are overexpressed in cholangiocytes proliferating after bile duct ligation (BDL) in the rat, in association with enlarged bile duct mass and with enhanced estradiol serum levels. Cholangiocyte proliferation, during BDL, is impaired by estrogen antagonists (tamoxifen, ICI 182,780) which furthermore, induce the overexpression of Fas antigen and activate apoptosis of proliferating cholangiocytes. 17beta-estradiol stimulates, in vitro cholangiocyte proliferation, and this effect is individually blocked by tamoxifen or ICI 182,780. Cholangiocyte proliferation during BDL was associated with an enhanced protein expression of phosphorylated extracellular regulated kinases (ERK)1/2 which is, in contrast, negatively modulated by tamoxifen in association with its antiproliferative effect. This indicates a major involvement of the ERK system in the estrogen modulation of cholangiocyte proliferation.

Retinal microcirculation as revealed by SEM corrosion casts in the rat.

The morphology of the retinal microcirculation has been extensively studied by different techniques. Nevertheless, some problems concerning the capillary bed lamination and pre- and postcapillary patterns have not yet been clarified. In the present study the SEM corrosion cast technique was employed to study the three-dimensional relationships of rat retinal vessels and to follow the smallest vascular branches. Rat retina is considered a useful experimental model for a number of pathologies which affect the microvascular bed deeply. Two precapillary patterns have been observed. Precapillary arterioles gave rise to capillaries both as terminal branches or as collaterals. The former pattern of ramification allows only a regulation of flow in a whole group of capillaries downstream, the latter pattern could provide a finer regulation of blood flow. SEM corrosion casts have shown very well the lamination of the capillary bed: one can easily realize this by seeing the overlapped meshes of the two different planes, vessels in between the two capillary laminae can always be followed from one meshwork to the other. This three-dimensional organization is an interesting model for retinal circulation because it shows many features in common with the retina of humans and primates.

[MDR (multidrug resistance) in hepatocarcinoma clinical-therapeutic implications]. / MDR (multidrug resistance) nell'epatocarcinoma: implicazioni clinico-terapeutiche.

Our purpose was to summarize current knowledge on "multidrug resistance", or MDR, an intrinsic or acquired cross resistance to a variety of structurally and functionally unrelated drugs, still representing one of the major problems in the therapy of cancer and other diseases. MDR depends on various mechanisms, the best known being the activity of ABC transport proteins, mainly Pgp, MDR1 gene product,and MRPs; but also other transporters can cause resistance, for example TAP, a peptide transporter, CFTR, cystic fibrosis transmembrane regulator, ABCG2, or breast cancer resistance protein (BCRP) and LRP, lung resistance protein. MDR has been detected in nearly all types of cancer, because it affects many organs and can occur against a wide number of drugs; it is frequent even in other diseases, such as epilepsy and HIV. We focused on MDR phenomenon in HCC, one of the commonest tumors in the world, and one of the most resistant to pharmacological treatment. This characteristic might be partly determined by a link between MDR and angiogenic phenotypes. The relationship between MDR in hepatocellular carcinoma and the effectiveness of therapeutic treatments has been particularly examined. Finally, the importance to overcome the strong chemoresistance of hepatocellular carcinoma with methods alternative to drugs, namely gene therapy, which makes use of antisense oligonucleotides and anti-MDR1 ribozymes, has been pointed out.

Contribution of intestinal smooth muscle to Crohn's disease fibrogenesis.

Mesenchymal cells transdifferentiation and extracellular matrix deposition are involved in the fibrotic process of Crohn's disease (CD). Mesenchymal smooth muscle cells (SMCs) de-differentiation, driven by Platelet-derived growth factor (PDGF) that counteracts Transforming growth factor (TGF-ß) has been studied in vascular muscle. The role of SMCs in intestinal fibrogenesis is still not clearly elucidated. Aim of the study was to evaluate the possible myogenic contribution to CD fibrotic process through the comparative analysis of histological, morphometric and molecular alterations occurring in human smooth muscle. Full thickness specimens were obtained from CD (non-involved and stenotic tracts) and healthy (control) ileum. Tissues were processed for histological and immunohistochemical (IHC) analyses and SMCs were isolated from the muscularis propria for morphofunctional and molecular (qPCR) analyses. CD stenotic ileum showed a significant increased thickness of all layers compared to CD non-involved and control ileum. IHC revealed an overexpression of α-smooth muscle actin and collagens I-III throughout all intestinal layers only in stenotic tracts. The two growth factors, PDGF and TGF-ß, showed a progressive increase in expression in the muscle layer from CD non-involved to stenotic tracts. Freshly isolated SMCs presented alterations in CD non-involved tracts that progressively increased in the stenotic tracts consisting in a statistical increase in mRNA encoding for PDGF-ß and collagen III, paralleled to a decrease in TGF-ß and Tribbles-like protein-3 mRNA, and altered morphofunctional parameters consisting in progressive decreases in cell length and contraction to acetylcholine. These findings indicate that intrinsic myogenic alterations occur in CD ileum, that they likely precede stricture formation, and might represent suitable new targets for anti-fibrotic interventions.

Polycystic liver diseases.

Polycystic liver diseases (PCLDs) are genetic disorders with heterogeneous etiologies and a range of phenotypic presentations. PCLD exhibits both autosomal or recessive dominant pattern of inheritance and is characterized by the progressive development of multiple cysts, isolated or associated with polycystic kidney disease, that appear more extensive in women. Cholangiocytes have primary cilia, functionally important organelles (act as mechanosensors) that are involved in both normal developmental and pathological processes. The absence of polycystin-1, 2, and fibrocystin/polyductin, normally localized to primary cilia, represent a potential mechanism leading to cyst formation, associated with increased cell proliferation and apoptosis, enhanced fluid secretion, abnormal cell-matrix interactions, and alterations in cell polarity. Proliferative and secretive activities of cystic epithelium can be regulated by estrogens either directly or by synergizing growth factors including nerve growth factor, IGF1, FSH and VEGF. The abnormalities of primary cilia and the sensitivity to proliferative effects of estrogens and different growth factors in PCLD cystic epithelium provide the morpho-functional basis for future treatment targets, based on the possible modulation of the formation and progression of hepatic cysts.

New insights into liver stem cells.

Hepatic progenitor cells are bi-potential stem cells residing in human and animal livers that are able to differentiate towards the hepatocytic and the cholangiocytic lineages. In adult livers, hepatic progenitor cells are quiescent stem cells with a low proliferating rate, representing a reserve compartment that is activated only when the mature epithelial cells of the liver are continuously damaged or inhibited in their replication, or in cases of severe cell loss. Hepatic progenitor cell activation has been described in various acute and chronic liver diseases. Their niche is composed by numerous cells such as Hepatic Stellate Cells, endothelial cells, hepatocytes, cholangiocytes, Kupffer cells, pit cells and inflammatory cells. All these cells, numerous hormones and growth factors could interact and cross-talk with progenitor cells influencing their proliferative and differentiative processes. Hepatic progenitor cells and their niche could represent, in the near future, a target for therapeutic approaches to liver disease based on cell-specific drug delivery systems. Isolation and transplantation of hepatic progenitor cells could represent a new approach for therapy of end-stage chronic liver diseases, as they offer many advantages to transplantation of mature hepatocytes. The possibility of applying stem cell therapy to liver diseases will represent a major goal in this field.

Estrogens stimulate the proliferation of human cholangiocarcinoma by inducing the expression and secretion of vascular endothelial growth factor.

BACKGROUND: Estrogens may induce the proliferation of neoplastic cells by activating neo-angiogenesis. AIM: To evaluate the effect of estrogens on the expression of vascular endothelial growth factor (VEGF) and related receptors (VEGF-R) in human cholangiocarcinoma and the role played by VEGF in mediating the proliferative effects of estrogens. METHODS: Seven biopsies of intra-hepatic cholangiocarcinoma and the HuH-28 cell lines were investigated. Cell proliferation was measured by both PCNA Western blot and MTS proliferation assay. RESULTS: By immunohistochemistry, biopsies of human cholangiocarcinoma stained positively for VEGF-A and VEGF-C and related receptors. HuH-28 cells expressed VEGF-A, -C, and VEGFR-1, -2, -3 and, their protein level was enhanced by 17beta-estradiol in association with the stimulation of cell proliferation. 17beta-Estradiol-stimulated proliferation of HuH-28 cells was blocked by 70% by VEGF-TRAP, a receptor-based VEGF inhibitor. 17beta-Estradiol induced the secretion of VEGF in the supernatant of HuH-28 cells. The stimulatory effect of 17beta-estradiol on the protein expression of VEGF-A, VEGF-C and VEGFR-1, -2, -3 was blocked by antagonists of ER (Ici182,780) or insulin-like growth factor 1-receptor (alphaIR3). CONCLUSIONS: With the limitations of experiments performed in a cell line, our study indicates that VEGF plays a major role in mediating the proliferative effects of estrogens on human cholangiocarcinoma.

Hepatic microcirculation and cholangiocyte physiopathology.

BACKGROUND: The peribiliary plexus (PBP) plays a fundamental role in supporting the functions of the biliary epithelium. After common bile duct ligation (BDL) progressive PBP proliferation is demonstrated. We have, recently, demonstrated that the biliary epithelium express Vascular Endothelial Growth Factor (VEGF), both subtype -A and -B and VEGF receptors. Taking in consideration the wide extension of PBP during BDL, aim of our study is to investigate the role of VEGF in stimulating angiogenesis and also in the modulation of epithelial cells proliferation. MATERIAL AND METHODS: Experimental studies were performed by evaluating the effects of: a) endogenous VEGF neutralization by chronic administration of anti VEGF-C antibody on cholangiocyte proliferation in BDL rats and; b) the hepatic artery ligation (HAL) immediately after BDL followed by treatment (7 days) with a recombinant of VEGF-A (administered through IP implanted minipumps) on cholangiocyte proliferative activities. RESULTS: Both administration of antiVEGF-C antibody and HAL decreases cholangiocyte proliferation. The decrease of cholangiocyte proliferation was associated with depressed VEGF-A protein expression. The administration of rVEGF-A to BDL, hepatic artery ligated rats prevented the decrease of cholangiocyte proliferation and VEGF-A expression as compared to BDL control rats. CONCLUSION: These data suggest that VEGF-C modulates the proliferative activities of cholangiocytes in experimental cholestasis and that circulating factors (i.e., VEGF) in the blood supply of the intra-hepatic biliary epithelium, play an important role in the balance between cholangiocyte proliferation/loss.

Microcirculation of the extrahepatic biliary tree: a scanning electron microscopy study of corrosion casts.

The microvascular arrangement of the extrahepatic biliary tree of the rat was studied by light microscopy (LM) and scanning electron microscopy (SEM) of vascular corrosion casts. The plexus that encircles the lumen of the common bile duct, observed by LM, showed a network of vessels of different diameter situated under the epithelium in the lamina propria. Parallel SEM observations of the same structure demonstrated the presence of 2 main vascular layers: an outer arterial and venous layer, corresponding to the larger vessels seen by LM, and a richer inner capillary layer just under the epithelium. On the luminal part of the corrosion casts, there were many round avascular empty pits that corresponded to the presence of small acinar glands distributed along the epithelium of the common bile duct. The rich subepithelial capillary network present in the rat, an animal without a gallbladder, may play an important role in the reabsorption of water and solutes from bile. Moreover, in pathological conditions (e.g. portal hypertension), liver blood flow may take a preferential collateral route through the intrahepatic peribiliary plexus into the relatively large diameter vessels of the extrahepatic peribiliary plexus because of the continuity of the 2 plexi.

A scanning electron microscopic study of liver microcirculation disarrangement in experimental rat cirrhosis.

Hepatic microcirculation has been related to liver function in several studies. The principle of this relationship lies in the sequential distribution of blood from the feeding vessels of the hepatic acinus to the central vein. This study was undertaken to investigate the progressive changes at different sites of the liver microvascular bed in the developing cirrhosis, both by light microscopy and scanning electron microscopy of corrosion casts. Experimental cirrhosis was induced with intragastric carbon tetrachloride. The most important vascular changes progressively observed are the reduction of the distance between the pre- and postsinusoidal vessels, the presence of newly formed shunting vessels bypassing the sinusoids and, finally, the development of a perinodular vascular plexus composed of pre- and postsinusoidal vessels. Newly formed vessels grow through preformed tissue septa. These vascular modifications make any zonal gradient hardly possible. The loss of the zonal gradient of perfusion could highly modify liver function, along with the structural changes of hepatic laminae. Hepatocyte regeneration cannot recover the original vascular relationships: this makes the morphological and functional destructuralization of cirrhotic liver irreversible.

Hepatic microcirculation and peribiliary plexus in experimental biliary cirrhosis: a morphological study.

BACKGROUND & AIMS: The peribiliary plexus plays a fundamental role in supporting the secretory and absorptive functions of biliary epithelium. Little information is available on the rearrangement of the peribiliary plexus during conditions associated with ductular proliferation. This study investigated the chronological modulation of bile duct and peribiliary plexus proliferation after common bile duct ligation in the rat. METHODS: Light microscopy and scanning electron microscopy vascular corrosion cast technique was used to study the architecture of the peribiliary plexus in rats with 1, 2, and 4 weeks of common bile duct ligation or in sham-operated controls. RESULTS: After 1 week of common bile duct ligation, no evident change of hepatic microvasculature was observed despite significant proliferation of bile ducts. After 2 and 4 weeks, significant microvasculature proliferation was observed extending from the peribiliary plexus of bile tracts. Vascular proliferation coincides with the extension of portal tract connective tissue. No evidence of vascular proliferation or other morphological modifications was present at the level of sinusoids around the portal tracts. CONCLUSIONS: After common bile duct ligation, the peribillary plexus undergoes marked proliferation, thus supporting the increased nutritional and functional demands from the proliferated bile ductal system. However, the proliferation of the peribillary plexus only occurs after that of the bile ductal system.

Precapillary patterns and perivascular cells in the retinal microvasculature. A scanning electron microscope study.

The microvasculature of the rat retina was studied in male Wistar rats in order to examine the features of the precapillary vascular pattern and structure that could affect blood flow regulation. Vascular corrosion casts and partially digested tissue specimens were observed by scanning electron microscopy. Side branching rather than bifurcation was the predominant microvascular pattern in the arterial tree. Two types of precapillary arteriole were present, one with the characteristic pattern of a preferential channel; the other gave off capillaries as terminal branches. At the origin of arteriolar side branches, smooth muscle cells appeared to buckle the endothelial nuclei into the vascular lumen. It is concluded that the rat retinal microvasculature appears to be characterised by 2 distinctive features: (1) side branching of arterioles which allows preferential flow in the most superficial layers of the retina; (2) peculiar luminal restrictions of arterioles and capillaries which permit fine regulation of blood flow.

Microcirculation of the extra-ocular muscles of rats. A scanning electron-microscopic corrosion cast study.

Specific researches, employing corrosion casts, were performed on different skeletal muscles, but not on extra-ocular muscles (EOMs). The microvascular bed of EOMs was studied by the corrosion cast technique in the rat. Two histologically and physiologically different layers were present in the EOMs. On the whole, the capillary pattern of EOMs was less dense than in the other skeletal muscles. The EOM orbital layer turned out to have a higher number of transverse anastomoses and tuning-fork divisions than the global layer had. These different microcirculatory patterns can be related with the physiological function and the anatomical situation of the EOMs.

Vitreal alterations in retinitis pigmentosa: biomicroscopic appearance and statistical evaluation.

The authors present a biomicroscopic evaluation of vitreal alterations in a large group of patients affected by primary retinitis pigmentosa (RP). 286 RP patients (571 eyes), 153 (305 eyes) males and 133 (266 eyes) females, have been studied; the mean age of this whole group was 37.26 + or - 14.93 years (age range: 5-77). Vitreal static and dynamic biomicroscopy was performed on fully dilated pupils by means of a Haag-Streit 900 slit-lamp and high-power positive precorneal lenses (+90 and +78 dpt Volk lenses). Most patients showed floating cottonball-like condensations (26.824%) often associated with fibrillary degeneration (15.88%), while non-pigmentary vitreal particulation was detected in 26.609% of cases and the pigmentary type in 12.017%, respectively. Posterior vitreal detachment was detected alone in only 0.43% of cases while 18.24% of examined eyes showed no vitreal alterations. A high statistical correlation between vitreal aspects and pigmentary grading of the fundus oculi (p = 0.0001), as well as duration of the disease (p = 0.0074), was found; at the same time, no statistical correlation with refractive error was demonstrated (p = 0.47).

Immunohistochemical features of bile duct epithelial cells in normal and experimental liver conditions.

It is well known that estrogen (E) modulates the processes of liver growth and regeneration. However, while estrogen receptors (Er) have been detected in hepatocytes, little is known on the occurrence of Er in cholangiocytes and the role of E on the physiopathology of the biliary epithelium. The purpose of this study was to investigate the occurrence of Er and their alpha or beta subtypes in cholangiocytes of normal and Bile Duct Ligated (BDL) rats and to evaluate the role and mechanisms of E in the modulation of cholangiocyte proliferation. In this study normal and BDL rats (utilized as experimental model of cholestasis) were used. Er alpha and beta subtypes, CK-19, PCNA and Fas were analysed by immunohistochemistry. The antiestrogens tamoxifen or ICI 182,780 were administered in the BDL group and the effects on cholangiocyte proliferation (bile duct mass) and apoptotic phenomenon (Tunel and Fas expression) were evaluated. Our results demonstrated that cholangiocytes express both Er-alpha and Er-beta subtypes, while hepatocytes only express Er-alpha. The increased percentage of cholangiocytes during BDL-induced proliferation was correlated with Er and PCNA expression and with enlarged Bile Duct Mass (BDM). Treatment of BDL rats with antiestrogens induced: i) inhibition of cholangiocyte proliferadon as indicated by the decreased BDM and PCNA expression; ii) over-expression of Fas antigen in cholangiocytes and induction of apoptosis (TUNEL) and iii) inhibition of cholangiocyte secretory activities. In condusion, our findings demonstrate that cholangiocytes express Er which are up-regulated during cholangiocyte proliferation. Inhibition of Er with antiestrogens blocks cholangiocyte proliferation and triggers apoptosis of Fas+ cholangiocytes suggesting a crucial role of estrogens in modulating cholangiocyte proliferation during bile duct obstruction.

Ochronotic arthropathy: structural and ultrastructural features.

Fragments of articular cartilage and synovial membrane in a case of ochronosis were studied by light microscopy (LM), polarized light, and transmission electron microscopy (TEM). Granular and/or shard-shaped pigments were observed in the synovia, cartilage, and subchondral tissue, and dispersed pigment was also seen in the synovial fluid. Zones of the articular cartilage surface showed small erosions near shards, and sometimes, when the degenerative process was in an advanced stage, a substitutive fibrosis of the cartilage edge was demonstrated. LM and TEM observations of the samples studied revealed an alteration of collagen fibrils that appeared wavy and sometimes fragmented with loss of periodicity. They were always mixed with the dispersed pigment. A peculiar finding that characterized this ochronotic case was the complete absence of inflammatory infiltrates or signs of monocyte-macrophage activation. These structural and ultrastructural observations suggest that the pigment deposition in the articular surfaces was due to the synovial fluid circulation and partially to subchondral blood flow, which transports and stores the ochronotic pigments in the synovia and cartilage. These etiopathologic elements associated with the mechanical pathogenesis naturally present in the joints can contribute to the explanation of the pathogenesis and origin of ochronotic arthropathy.

The hepatic microcirculation in experimental cirrhosis. A scanning electron microscopy study of microcorrosion casts.

The experimental model of liver cirrhosis induced by intragastric administration of CCl4 reproduces not only the histological picture of the postnecrotic cirrhosis but also its pathophysiological features. Corrosion casts of livers affected by CCl4-induced cirrhosis show the loss of the lobular pattern. Once the cirrhosis has completely developed, the whole microvascular bed appears to be composed of groups of sinusoid nodules of diameters varying between 0.3 and 1.5 mm.. Pre- and post-sinusoidal vessels and anastomoses between the former and the latter are mainly located at the perinodular spaces. This microvascular situation modifies the normal perfusion gradient within the parenchyma. Nevertheless, it can allow a still viable function.

Hepatic microcirculation as a morpho-functional basis for the metabolic zonation in normal and pathological rat liver.

The hepatic microcirculation is well known as a fundamental component of the liver structure, deeply involved in the zonal organization of the acinar structure. In cirrhosis, the microvascular tree shows dramatic changes that would heavily influence the development of the disease. When the cirrhosis becomes evident the result is a progressive organ failure, also in presence of only moderately decreased hepatocyte volume. The aim of this research was to compare the role of microcirculation of the hepatic zonation in normal and cirrhotic livers. Cirrhosis was experimentally induced in 36 rats following a controlled intragastric CCl4 administration. Cirrhotic and control normal livers were processed for routine light microscopy, histoenzimology, and scanning electron microscopy vascular corrosion cast. Control livers showed normal hepatic structure and microvascularization; enzymatic activities were constantly and normally distributed. In CCl4-treated animals LM showed a characteristic micronodular cirrhosis in all livers. Vascular corrosion casts under the scanning electron microscope displayed a progressive reduction of the distance between pre- and post-sinusoidal vessels and the presence of newly formed perinodular plexus. The histoenzymatic analysis demonstrated the loss of zonation in the cirrhotic parenchyma. Moreover, the sinusoid/hepatocyte ratio was significantly reduced, because of the presence of two or more hepatocyte thick laminae during the scarring development. The altered microcirculation in cirrhosis also changed the normal acinous metabolic gradient. The histoenzymatic study revealed a zonal rearrangement of the cirrhotic liver metabolic activity, that leads to a progressive hepatic failure. These data confirm the fundamental importance of the normal relationship between the hepatocyte laminae and the sinusoids for the preservation of a normal zonation which represents the basis for a normal liver function.

Liver metabolic zonation and hepatic microcirculation in carbon tetrachloride-induced experimental cirrhosis.

The exact cause of the hepatic failure in liver cirrhosis is currently unclear, and two main theories have been proposed: the first is based on the altered hepatocyte function (sick hepatocyte hypothesis); the second on the abnormal hepatic architecture (intact hepatocyte hypothesis). Moreover, the microcirculation, a fundamental component in liver structure, shows dramatic changes in cirrhosis that would heavily influence the development of the disease. In order to determine the importance of the microvascular alterations on liver morphofunctional features in experimentally induced cirrhosis, their relationships with structural, ultrastructural, and histoenzymological hepatocyte modifications were investigated. Experimental cirrhosis was induced with controlled intragastric CCl4 administration. Scanning electron microscopy of the vascular corrosion cast technique, associated with light microscopy, transmission electron microscopy, and histoenzymology techniques were employed. The results demonstrated a characteristic micronodular cirrhosis in all the livers studied; the microcirculation displayed the presence of newly formed perinodular plexus. Inside the nodule, areas with two or more hepatocyte-thick laminae were present. Moreover, a rearrangement of the hepatocyte quantitative ultrastructure without real pathological changes and a loss of normal metabolic lobular zonation were noted in the liver parenchyma. These findings support the concept that the progressive modifications of the microcirculation during experimental CC14 cirrhosis modify not only the normal blood flow direction, but also the normal hepatic metabolic gradient with a loss of the normal hepatocytic zonation.

Hepatic microvascular features in experimental cirrhosis: a structural and morphometrical study in CCl4-treated rats.

BACKGROUND/AIMS: In this study, a detailed morphometrical analysis of the hepatic microvasculature in the different zones of hepatic parenchyma was performed in normal and cirrhotic rat liver (CCl4-induced). The aims were to detect, in CCl4-induced cirrhosis, the real presence of the "capillarization" of hepatic sinusoids and to assess alterations of the sinusoid/parenchyma ratio within the nodule. METHODS: Cirrhosis was promoted by controlled intragastric CCl4 administration. Scanning electron microscopy of the vascular corrosion cast technique associated with light microscopy and transmission electron microscopy were used. RESULTS: Evidence of connective tissue in the space of Disse was found only in sinusoids located near portal tracts or large fibrotic areas, and this was also confirmed by laminin immunohistochemistry. In contrast, all the intranodular sinusoids lacked real basal membrane and connective fibers in the space of Disse and, displayed normal fenestrations. The parenchymal area, sinusoidal area, mean sinusoidal area, sinusoidal perimeter, hepatocyte area and the reciprocal ratios were all considered in the morphometrical analysis. The sinusoids were of uniform size in the periportal, periseptal and pericentral areas of the cirrhotic liver without the typical zonal differences of the normal liver. The areas occupied by sinusoids per unit of parenchyma and the sinusoid/hepatocyte interfaces disposable for metabolic exchanges were markedly smaller (p<0.01) in cirrhotic than normal liver. CONCLUSION: Our findings indicate that capillarization of hepatic sinusoids occurs only in very limited regions of the cirrhotic parenchyma, and thus this phenomenon does not have relevant functional consequences. Furthermore, the cirrhotic parenchyma appears not to be supplied by sinusoids and lacks features of zonation, which is a condition that could play a major role in the development and progression of liver failure.