Increases in unconjugated bilirubin (UCB) are found consistently in the bile of patients with pigment gallstones, even though total bilirubin concentration sare normal or low. We have published a study of the solubilization of UCB in simple
auenous
and
bile salt solutions, and the study revealed that the bile was almost entirely in the monoanion form at physiologic values and the two carboxyly in the monoanion form at physiologic values and the two carboxylic pKa values were widely separated.
The
data, however, were not ideal due to possible effects of crystal size, metastability and long incubation time.
In the present study, the problems were minimized by rapid equilibrium partition of UCB from solutions in CHCl3 into buffered aqueous NaCl, followd by a repeat aqueous partition of the residual UCB in the CHCl3 phase By determining the effects on
partition ratios of varying the UCB in the CHCl3 phase, we could assess self-association of UCB anions in the aqueous phase.
Our study demonstrates that 1) aquenous solubility of UCB is less than 1% of its maximam concentration in normal plasma and bile, 2) the unbound ocncentration of HB- woiuld decrease with decreaing bile pH, 3) the ion products of bile salts would
increas
with increasing bile pH. 4) defective acidification of bile in the gallbladder might favor precipitation of calcium bilirubinates.
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