Response of Bile Flow, Biliary Lipids and Bile Acid Pool in the Pig to Quantitative Variations in Dietary Fat

Abstract

Bile flow, biliary lipids and bile acid pool have been studied in growing pigs adapted to a semipurified diet of 2, 10 or 20% lard. After a 5-day period of apparent digestibility measurement, bile secretion was studied in previously fistulated pigs. The apparent digestibility of lard was maintained at a very high level, whatever quantity of lard was ingested. Daily bile acid output was 49% higher with the 10% lard diet than with the 2% lard diet, whereas no further increase was observed with the 20% lard diet. There was a direct relationship between bile acid output and pool size. Biliary phospholipid output increased by 29.0% between 2 and 10% dietary lard and by 69.5% between 10 and 20% lard. The corresponding rise in biliary cholesterol output was +33% between 2 and 10 or 10 and 20% lard in the diet. A study of biliary kinetics showed that this adaptation of biliary lipid to dietary fat was observed whatever time of the light/dark cycle was considered. These results, together with a recent demonstration of the implication of endogenous phospholipids in fat digestion, suggested that, in the course of biliary lipid adaptation to dietary fat content, biliary phospholipid could act in synergy with bile salt, resulting in the maintenance of excellent dietary fat digestion.

Nutritional Regulation of Pancreatic and Biliary Secretions

“…A general conclusion, however, reconciles the results of all the previously mentioned authors, when considering the absolute rate of lipid consumption : secretion of bile salts is definitely stimulated by fat supplementation of a diet initially low in lipid or lipid-free ; the secretion rate of bile salts remains unchanged when fat supplementation is superimposed on a diet whose lipid content increases from 70-100 g/kg to 150-200 g/kg. This is confirmed by our own experiment in pigs fed with different lipid-containing semisynthetic diets (Juste et al 1983). However, the reason why the secretion rate of bile salts does not increase further remains unclear.…”

“…Indeed, if the recycling frequency were responsible for differential secretion rates, the latter would have been essentially limited to digestive periods. Accordingly, dietary fat content would affect the bulk of bile acid absorbed per unit time, without modifying the rhythm of that absorptive activity (Juste et al 1983). Findings obtained from intestinal loops in the rat (Sklan & Budowski, 1977;Fondacaro & Wolcott, 1981) would support our proposition: the rate of transport of the bile acid taurocholate across the jejunal or ileal walls depends on the type and concentration of lipid added to the luminal medium.…”

“…It has been demonstrated in pigs that cholesterol secretion rate rises to the same extent whether lard is increased from 20 to 100 g/kg or from 100 to 200 g/kg in the diet (Juste et al 1983). Biliary cholesterol output, however, is the same with 100 or 200 g sunflower oil/kg in the diet, and in this case, much higher than following a lard diet.…”

“…In rats fed on a 200 g maize oil/kg diet, the phospholipid secretion rate was 1.5 times higher than that observed with a 70 g maize oil/kg diet (Boquillon & Cltment, 1979). It has been demonstrated (Juste et al 1983) that in pigs the phospholipid output increases moderately when bile acid output rises sharply, when there is a change from a low-to a medium-level lard diet, whereas the phospholipid output increases much more when bile acid output is in a steady-state, when changing from a medium-to a high-level lard diet. This was interpreted as a possible synergic action between phospholipid and bile acid in the course of biliary lipid adaptation to dietary fat content, resulting in the maintenance of virtually complete dietary fat absorption (Juste et al 1983).…”

“…The secretion rate of biliary phospholipids has been shown to be either essentially unchanged whatever the degree of saturation of dietary long-chain triglycerides (Paul & Ganguly, 1976;Juste et al 1983) or it is stimulated by largely unsaturated triglycerides (Redinger et al 1973;Boquillon & Cltment, 1979). It is now clear that there is marked increase in the unsaturation of biliary phospholipids as a consequence of eating unsaturated long-chain triglycerides (Paul & Ganguly, 1976; C. Juste unpublished results).…”