Dietary Factors Affecting Biliary Lipid Secretion in the Rhesus Monkey A Mechanism for the Hypocholesterolaemic Action of Polyunsaturated Fat?*

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Abstract
Using an experimental model which permits representative bile sampling whilst maintaining an almost “intact” enterohepatic circulation, it was found that different diets markedly influenced biliary lipid secretion in the rhesus monkey. In different studies, we have previously shown that bile volume, bile salt, phospholipid and cholesterol secretion rates were significantly less in animals given a low fat commercial diet then in monkeys given a second commerical diet with higher fat content.The present paired studies confirmed that in the same animals, the higher fat diet stimulated bile volume and biliary lipid secretion. On the higher fat diet there was no change in bile salt concentration or in pool size, the greater secretion rate being due to a greater bile volume and to more frequent circulations of the bile salt pool.Since the major differences between the two commercial diets were in fat and calories, the effect of supplementing the low fat diet with individual additives of olive, corn and medium chain triglyceride oil and with 40% dextrose was examined in further paired studies.In six monkeys, supplements of mono‐unsaturated olive oil had no effect on biliary lipid secretion, but in seven animals given comparable doses of polyunsaturated corn oil, there was a significant increase in biliary bile salt, phospholipid and cholesterol output.The addition of medium chain triglyceride oil or of 250 ml of 40% dextrose did not change biliary lipid secretion rates. None of the dietary manipulations significantly altered cholesterol solubility in bile.In monkeys where hepatic bile salt synthesis had been maximally induced by partial biliary diversion (33.3% interruption of the EHC), corn oil no longer increased bile salt secretion suggesting that the stimulatory effect of corn oil was due to stimulation of bile salt synthesis.It is postulated that the increased turnover of bile salts seen after feeding corn oil, with a resultant acceleration in cholesterol catabolism, may explain, at least in part, the hypocholesterolaemic action of polyunsaturated fat.

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