C. Balabaud

Nerves and perisinusoidal cells in human liver

Unmyelinated nerve fibres are visible in the human hepatic lobule. They extend through the Disse space, surrounded by Schwann cell processes, often close to perisinusoidal cell processes. A few bare nerve endings or varicosities are found contiguous to either hepatocytes or perisinusoidal cells. These nerve endings or varicosities contain large and small granular vesicles and small clear vesicles. This heterogeneity probably corresponds to the presence of various neurotransmitters (noradrenaline, acetylcholine, various neuropeptides...). The effect of nerves on perisinusoidal cells has not yet been elucidated. However, the location, shape, morphology and origin of perisinusoidal cells would suggest that they play a role in the hemodynamic regulation of sinusoidal blood flow. It has recently been shown how important non-parenchymal-parenchymal communication is in the action of nerves on glucose release by hepatocytes; the cell to cell communications may also apply to nerves and sinusoidal cells for the hemodynamic regulation of sinusoidal blood flow.

Perisinusoidal fibrosis of the liver in patients with thrombocytopenic purpura

10 patients with thrombocytopenic purpura (TP) underwent splenectomy. Eight of these patients had idiopathic TP (certain or probable). All had normal liver function tests. Liver histology of the surgical biopsy was normal with the exception of a non specific mild portal infiltration in 6 cases. On Sirius red staining the perisinusoidal network was normal in 3 cases, mildly or moderately increased in 5 cases and often associated with perivenular fibrosis. Collagen types I, III, IV, laminin and fibronectin were increased in the 8 biopsies tested. On semi-thin sections, numerous Kupffer cells were observed. Under the electron microscope, sinusoidal abnormalities were very similar in all 7 patients studied: numerous Kupffer cells containing abundant lysosomes, numerous collagen bundles in the Disse space, active endothelial cells, transformation of some perisinusoidal cells into cells with some of the characteristics of fibroblasts (increased RER) and myofibroblasts (peripheral condensations of the filamentous network), increased fragments of basement membrane-like material. In two cases there was an increase in the number of perisinusoidal cells loaded with lipids. The similarity of the lesions and the absence of other fibrogenic causes (except in 2 cases) suggest that TP may represent another group of diseases with perisinusoidal fibrosis. The aetiology of fibrosis remains unknown but platelet derived growth factor and activated macrophages may play a major role.

The sinusoidal barrier in alcoholic patients without liver fibrosis. A morphometric study.

Alcohol induces morphological changes in the endothelial and perisinusoidal cells at the fibrotic stage of alcoholic liver diseases. Directly or indirectly, through hemodynamic disturbances linked to the enlargement of steatotic hepatocytes, alcohol may modify this barrier before the onset of fibrosis. Liver biopsies were obtained from control and from alcoholic patients and perfusion-fixed. Volume and surface densities of endothelial cells, perisinusoidal cells and their processes were measured. Liver histology was normal in the 2 groups except for steatosis in the alcoholics. Volume densities represented 8.2%, 4.7% and 3.2% of the sinusoid in controls for endothelial cells, perisinusoidal cells and their processes whereas surface densities represented respectively 0.5, 0.23, 0.21 m2/cm3 of sinusoid. Morphometric values were not significantly different in the alcoholic patients. In none of the alcoholic patients did fine morphological studies of sinusoidal cells give any indication of the possible evolution of the alcoholic disease towards fibrosis. These results indicate that in the group of patients studied, alcohol, before the fibrotic stage, did not significantly alter the sinusoidal barrier.

The sinusoidal barrier in rats with portacaval anastomosis: a morphometric study.

Shunting of portal blood in the rat leads to liver atrophy and to an increase in arterial blood flow with microcirculatory disturbances. The aim of this study was to investigate the effects of these disturbances on the liver sinusoidal barrier (endothelial and perisinusoidal cells) using morphometric techniques. Rats with portacaval anastomosis (PCA) and sham operated pair-fed controls were studied 3 months after the shunt. Sinusoidal volume density in PCA increased but not significantly and the volume density (Vv) of total endothelial (EC) and perisinusoidal cells (PSC) increased by 104.54% compared to sham operated pair-fed rats. The increase of EC Vv was not associated with an increase in surface density (Sv) suggesting a fall in the number of small fenestrations and an increase in cell thickness. This interpretation supports the morphological observations. The increase of PSC Vv was mainly related to the increase in their subendothelial processes Vv and not to that of the cell body Vv. Lipids Vv and RER Sv expressed per sinusoidal cells remained unchanged suggesting that the balance between the 2 hypothetical functions of the PSC, namely fibrogenesis and storage of vitamin A, was maintained. In conclusion, changes of EC and PSC after PCA result mainly in thickening of the sinusoidal barrier. This increase may impair exchanges between the sinusoidal lumen and Disse space and contribute to functional abnormalities.

Removal of cellular debris formed in the Disse space in patients with cholestasis.

Using electron microscopy, we investigated how cellular debris, formed in the Disse space during cholestasis, was cleared. Ten patients with cholestasis of varied origin and severity were studied and compared with 10 controls without liver disease. In cholestatic patients, sinusoidal cells contained variable amounts of amylase PAS-positive material. In clean perfusion-fixed sinusoids the endothelial cells often appeared swollen and active, with few fenestrations. Hepatocyte blebs and cellular debris were sometimes seen in the Disse space. Two mechanisms were apparently involved in the clearing process: phagocytosis by macrophages either infiltrated into the Disse space, or forming the barrier; and the passage of debris from the Disse space into the sinusoidal lumen through the endothelial wall. Debris was either forced through enlarged pores or through the wall, with a progressive invagination followed by an outpouching in the lumen. The force, possibly provided by endothelial massage, may not be sufficient to push out cellular debris from the Disse space; morphological data seemed to indicate that endothelial damage may be a necessary factor. Debris present in the lumen was phagocytized by numerous active macrophages. Cellular debris was not observed in the Disse space of control patients.

Microscopic Anatomy of the Intrahepatic Circulatory System

The liver in mammals has a dual blood supply. Approximately 80% of the blood entering the liver is mildly oxygenated venous blood supplied by the portal vein, while the remainder is well oxygenated and supplied by the hepatic artery. Within the liver distributing branches of the portal vein and hepatic artery run parallel and, after repeated branching, terminal branches of these vessels (portal venules and hepatic arterioles) supply blood to the hepatic sinusoids. The sinusoids are the principal vessels involved in the transvascular exchange between the blood and parenchymal cells. Branches of hepatic arterioles also supply blood to the liver capsule as well as the bile ducts, where they feed a peribiliary plexus of capillaries which, in turn, drains into the sinusoids. Portal and arterial blood flowing through the sinusoids is collected in small branches of hepatic veins (central or terminal hepatic venules) through which the blood is returned via larger hepatic veins to the inferior vena cava. Lymphatic vessels originate as blind-ending capillaries in the connective tissue spaces (portal tracts) close to the portal veins and hepatic arteries. The fluid contained in these lymphatic vessels flows toward the hepatic hilus and eventually into the cysterna chyli.

Hepatic Blood Flow in Rats with Portal Branch Ligation

Hepatic arterial blood flow (HABF) in the liver lobes and splanchnic nonhepatic arterial blood flow were measured in rats with and without right portal branch ligation for 1 month using 57Co microspheres. Portal branch ligation led to 60% atrophy of the ligated lobe and to hypertrophy of the nonligated lobe. In nonligated lobes of the portal branch ligation model and in the lobes of controls, HABF expressed per gram liver was comparable. In both models splanchnic non-HABF was also comparable. In the atrophic lobe, HABF remained constant; expressed per gram liver, it increased. In this lobe the net result was a significant decrease in total hepatic blood flow (ml/min/g liver).