On the stratification of human bile and its importance for the solubility of cholesterol.

Stratification (layer formation) is noted in vitro in hepatic bile collected after interruption of the enterohepatic circulation. Hepatic bile is still layered after more than 12 hr when collected in this way (continuously or in fractions) in a bag made of a semipermeable membrane (simulating an atonic gall bladder) and concentrated. Cholesterol solubility is very slight in the upper layer. This phenomenon may be important for precipitation of cholesterol and the formation of gallstones, since the enterohepatic circulation is interrupted when bile is stored and concentrated in the gall bladder. This condition may be prolonged by temporary stasis, which has always been considered one of the main factors in the formation of gallstones.