The importance of keeping bile salts in their place.

Abstract

Bile contains several substances which are partially absorbed from the intestine and secreted again in the bile. They include urobilinogen, cholesterol,1 and possibly certain hormones2 and fat-soluble vitamins3. But the enterohepatic circulation of bile salts is unique in both its physiological importance and its efficiency.Conjugated bile salts have powerful detergent properties,4 which are important in stabilizing the supersaturated state of bile and in promoting fat digestion and absorption.5 These functions, and the complex metabolism undergone by bile salts, all take place in the context of the enterohepatic circulation and depend on its proper functioning. The enterohepatie circulation may be thought of as an endless flow of detergent through thc liver, biliary tract, small and to some extent large, intestine, and back to the liver again. Thanks to the gallbladder, this process occurs in bursts rather than continuously and it is estimated that the bile salt pool recirculates twice with each meal, or up to eight times a-day.6 The normal pool size being 3 to 4 g,7 this means that about 24 g of bile salts enters the duodenum each day. A striking feature of the enterohepatic circulation is its efficiency as a closed recycling system. Probably more than 99 % of the bile salts in the body are within the enterohepatic circulation at all times. The systemic blood contains less than 10 mg in all8 and none is detectable in the urine.9 A significant leak does occur into the stools, but the normal daily excretion of 15 to 20% of the pool represents a mere 3 to 4% escape at each turn of the cycle.10' 11 The efficiency of the enterohepatic circulation depends on several factors. First, the liver is avid in extracting bile salts from the blood.12 Isotope studies show the mean half-life of plasma cholic acid to be only 12-6 minutes.13 Such rapid clearance must be due to an active transport system, since it involves transfer of large polar molecules across the essentially lipid membrane of the liver cell.14 The same is true of biliary secretion which is also rapid.14 Labelled bile salt has been detected in the duodenum of a cholecystectomized patient within 20 minutes of intravenous injection.15 Secondly, having reached the duodenum, bile salts are prevented from regurgitating into the stomach by the competence of the pyloric sphincter. In normal subjects they are either undetectable or present in only trace amounts in the gastric juice.16 Thirdly, due to their low pKa, conjugated bile acids exist mainly in the ionized form at the pH of the upper small intestinal lumen.4 This minimizes any tendency to diffuse down electrochemical gradients into the blood or lymph17 and ensures that the intraluminal concentration remains high until fat absorption is complete.18 This physicochemical 'seal' depends upon bile salts remaining in the conjugated state, since free bile acids readily diffuse out of the jejunal lumen.17Deconjugation is within the capacity of many intestinal bacteria,'9 so that a fourth factor in maintaining the ef...

Inhibition of cholesterol transport in an intestine cell model by pine-derived phytosterols

“…In details, the bile salt was used 6-13 times higher concentration compared with previous studies of intestine cell model system (Field et al, 1997;Palmgren et al, 2005;Petruzzelli et al, 2009). The amount corresponds to the physiological condition in the Duodenum and small intestine of the human body because the 3-4 g of bile salt was secreted to Duodenum 8 times a day (around 24-32g per day) and reabsorbed in colonic enterocytes (Heaton, 1969;Hofmann, 1999), and the average volume of human Duodenum, the place of lipid digestion, was reported to be 275.5 ml from 105 people, aged from 13-93 years old (Suman, 2013). Based on these data, bile salt concentration is over 70 mM in the Duodenum and then is diluted by the volume of the small intestine.…”

The Gut Microbiota Affects Host Pathophysiology as an Endocrine Organ: A Focus on Cardiovascular Disease

“…CA and CDCA are then extensively conjugated in a two-step process to either glycine (75%) or taurine (25%), transported into bile via the bile salt export pump (BSEP), and subsequently stored in the gallbladder until their release into the duodenum after the ingestion of a meal [28]. The conjugation process increases the water-solubility and detergent properties of BAs, thus facilitating the emulsification and absorption of dietary cholesterol, triglycerides and fat-soluble vitamins [77].…”

Letter: Streptokinase and heparin in treatment of pulmonary embolism.

“…Streptokinase and Heparin in Treatment of Pulmonary Embolism SIR,-In the controlled clinkal trial of streptokinase and hepa-rin in the treatment of pulmonary em-bolism reported by Dr. D. A. Tibbutt and others (2 March,p. 343) the solution used as a loading dose contained (1) 0 9% saline or 5 % dextrose as the vehicle, (2) hydrocortisone 100 mg, and (3) streptokinase 500,000 units or heparin 5,000 units. The results of treatment in 30 patients entered in the trial appeared to demonstrate that the patients who received streptokinase showed a significantly greater evidence of thrombolysis on angiographic appearances.…”