Effects of dexamethasone and linoleic acid on hepatic secretion of biliary lipids and anionic polypeptide factor: In vivo and in vitro studies

Abstract

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 microg/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.