Effect of intrajejunal acidity on lipid digestion and aqueous solubilisation of bile acids and lipids in health, using a new simple method of lipase inactivation

Abstract

We have investigated whether acid-mediated bile acid precipitation, pancreatic enzyme inactivation and fatty acid partitioning occur in health when intraluminal pH falls below 5. In order to assess lipolysis and aqueous solubilisation of lipid, we first developed a new technique for inactivating lipase in jejunal aspirate (acid inactivation), and showed it to be more effective and simpler than the established technique (heat inactivation). We then studied 14 healthy subjects, aspirating jejunal content for three hours after a liquid meal, and pooling according to pH. Eighteen per cent of the total aspirate was collected at pH < 5 compared with 56% at pH > 6 (p < 0.01). Forty eight per cent of the bile acids were precipitated at pH < 5 compared with 18% at pH > 6 (p < 0.01), leading to a reduction in aqueous phase bile acid concentration at low pH (2.1 mmol/l at pH < 5 vs 5.8 mmol/l at pH > 6, p < 0.01). Lipase activity was reduced at low pH (133 IU/l at pH < 5 vs 182 IU/l at pH > 6, p < 0.01), leading to reduced lipolysis at low pH (14% at pH < 5 vs 32% at pH > 6, p <0.01). Aqueous phase lipid concentration was reduced at low pH (3.5 mmol/l at pH < 5 vs 12.5 mmol/l at pH > 6, p < 0.01). This reduction was less dependent on bile acid precipitation than on lipase inactivation and fatty acid partitioning. We conclude that intraluminal acidity influences aqueous solubilisation of bile acids and lipid in health.