Characteristics of conjugated bile salt absorption by hamster jejunum

Abstract

The physical state of conjugated bile salt during its passive absorption by the jejunum is not known and may be important in understanding the mechanism of jejunal lipid absorption. We studied the absorption of sodium taurocholate from media with and without oleic acid and monoolein and of sodium glycocholate and sodium glyco-deoxycholate from media without lipid. Everted hamster jejunal sacs were incubated in solutions which contained concentrations of bile salt ranging from zero to well above their critical micellar concentrations; the net amount of bile salt taken up by the tissue at each concentration was determined. The net absorption of sodium taurocholate and sodium glycocholate increased 2-fold at concentrations above their critical micellar concentrations; the net sodium glycodeoxycholate absorption was constant below and above its critical micellar concentration. Below their critical micellar concentrations, the net sodium glycocholate absorption was 1.5 times that of sodium taurocholate and 0.33 times that of sodium glycodeoxycholate. Above their critical micellar concentrations the net absorption of sodium taurocholate and sodium glyco-cholate were equal but sodium glycodeoxycholate was absorbed almost twice as rapidly as the cholate conjugates. Although fatty acids and monoglyceride were not present in all incubations, their presence did not affect the net bile salt absorption. The movement of sodium taurocholate from the tissue into the solution bathing the mucosal surface of everted jejunal sacs was found to be significant. The findings are consistent with, but do not prove, passive diffusion of intact primary micelles into the jejunal mucosa and support the concept that conjugated bile salts may facilitate the transport of lipid across the microvillous membrane.