Distribution of glycocholate in blood from human fetuses and adults.

Glycocholate binding by plasma proteins and erythrocytes from fetal and adult blood has been studied, and the results have been used to derive a compartmental model of the distribution of glycocholate in blood. This model assumes that glycocholate is distributed between the aqueous phase, albumin binding sites, binding sites on other plasma proteins, and erythrocytes. Whereas glycocholate binding by albumin was saturable [fetal blood: dissociation constant (0.5 mM), concentration of binding sites (11.3 mumoles/g protein); adult blood: dissociation constant (0.42 mM), concentration of binding sites (20.1 mumoles/g protein)], binding by other plasma proteins was not. The association of glycocholate with erythrocytes appeared to be based on partitioning rather than binding of the bile salt to specific sites. The value of the partition coefficient was 6.0. The compartmental model indicates that, in fetal blood, 46% of the glycocholate is in free solution, and 37% is bound to albumin. In blood from adults, the corresponding values are 31% in free solution and 59% bound to albumin.