Search

We studied and quantified the effect of cyclosporine A on hepatic F-actin on bile canalicular and basolateral membranes in rats fed either soybean lecithin, triacylglycerol-enriched diet, or low-fat diet by means of confocal laser scanning microscopy imaging. The phalloidin-FITC staining of F-actin was quite normal in the lecithin-cyclosporine A group but decreased significantly in the other cyclosporine A-treated groups (by 40% and 25% of control in triacylglycerol-cyclosporine A and cyclosporine A groups, respectively). The alteration of F-actin by cyclosporine A, related to cholestasis evidenced by a decrease in bile salt secretion, was prevented by dietary soybean lecithin and amplified by dietary soybean triacylglycerol. [ABSTRACT FROM AUTHOR]

We studied the effect of dietary soybean lecithin or triacylglycerol on hepatic Na+,K(+)-ATPase in cyclosporine A-treated rats by means of quantitative immunocytochemistry. Cyclosporine A-treated rats were fed lecithin or a triacylglycerol-enriched diet or a low-fat diet. As a control, one group was only fed the low-fat diet; the three other groups were treated with cyclosporine A solvent and received the low fat, lecithin, or triacylglycerol diet. Bile canalicular staining significantly decreased in all cyclosporine A-treated groups with the higher values in lecithin-fed rats. In basolateral membranes, no decrease was observed in the lecithin-cyclosporine group, in contrast to the other groups. The triacylglycerol-cyclosporine group had lower values in both membrane domains. The alteration of Na+,K(+)-ATPase by cyclosporine A was related to cholestasis evidenced by a decrease in bile salt secretion. These modifications were prevented by dietary soybean lecithin and amplified by dietary soybean triacylglycerol. [ABSTRACT FROM AUTHOR]

Synthetic glucocorticoids, such as dexamethasone, and diets enriched with unsaturated fatty acids have been shown to stimulate hepatic bile salt synthesis. This fact led us to investigate the effects of dexamethasone and linoleic acid supplementation on bile secretion. Cholesterol (Ch) and phospholipid secretions are bile acid dependent. Ch and phospholipid in bile are also highly bound to a small apoprotein, the anionic polypeptide factor (APF). In bile, APF may play a physiological role in stabilizing cholesterol:phospholipid vesicles and might also be important in the regulatory process of bile lipid secretion. In order to study the factors influencing bile secretion, the biliary secretion rates of bile lipids and APF were experimentally modulated in perfused rat liver (PRL) and HepG2 cells. As expected, dexamethasone induced an increase in the biliary secretion rate of bile salts (BS) in the two models (PRL: 34 up to 67 nmol/l/min/g liver; HepG2 cells: 234% vs. 100% in controls). The bile secretion rates for phospholipids (PRL: from 5 down to 1.5 nmol/l/min/g liver; HepG2 cells: 93 vs. 100% in controls) and APF (PRL: from 0.34 down to 0.12 µg/l/min/g liver; cells: 86 vs. 100% in controls) rapidly decreased independently from those of BS. The data from experimental cell models supplemented with linoleic acid indicated a correlation between the BS and APF levels (APF: 71 and 63%; BS: 161 and 197% vs. 100% in controls). The phospholipid level was regulated independently from that of APF and BS and increased (106 and 111% vs. 100% in controls), while Ch remained nevertheless unchanged. Our data showed that dexamethasone induced changes in bile and that linoleic acid clearly impaired the regulation exerted by the dexamethasone on bile lipids. [ABSTRACT FROM AUTHOR]

Isolated perfused rat liver was used to study the effects of constant taurocholate perfusion, with or without the addition of phosphatidylcholine unilamellar vesicles, upon both the bile salt-dependent and bile salt-independent secretion of bile. Taurocholate introduction increased bile flow and normalized the bile lipid secretion by restoring the bile salt-dependent secretion. At a flow rate of 30 ml/min, the liver was perfused by a single-pass method. The perfusion medium contained 17.5 μM taurocholate with or without 5.83 μM phosphatidylcholine. In light of a recent quantitative dynamic concept on the interphase partition of lipids, it was calculated that more than99% of the taurocholate reaches the liver as monomers and/or dimers. It was also deduced that the lipids were secreted in bile as small discoidal lipoprotein structures rather than unilamellar lipoproteic vesicles. During the course of the experiments (2 hr), the excellent criteria of viability of this model make it highly suitable for the investigation of hepatic metabolism. Furthermore, the addition of phosphatidylcholine unilamellar vesicles to the perfusate consitutes a potential vector for various liposoluble molecular species. [ABSTRACT FROM AUTHOR]

Phospholipids and cholesterol combine with a protein fraction (IgA and an acid polypeptide) in bile to form the bile lipoprotein complex. We wished to determine whether lysosomes participated only in IgA secretion or if their secretory role also involved the lipid components of the bile complex. This aspect was studied with a single acute injection of chloroquine, a lysosomotropic drug. The results show that a nonnegligible quantity of IgA travels through the lysosomes. In addition, phospholipid and cholesterol levels undergo a significant (P<0.05) decrease 1 hr after injection before increasing to normal levels. In contrast to the total inhibition of protein secretion (β-glucuronidase, acid phosphatase), a transitory decrease of the secretion of bile lipids takes place that suggest secretory mechanisms involving organelles other than lysosomes. [ABSTRACT FROM AUTHOR]

Lipoprotein lipase activity was determined in Zucker rats by assaying VLDL radioactivity. Animals were i.v. injected withH-oleic acid andC-glycerol with or without Triton WR 1339. This enzymatic activity was higher in fa/fa rats than in non-obese Fa/-rats. [ABSTRACT FROM AUTHOR]