125I Radioimmunoassay of serum ursodeoxycholyl conjugates.

A radioimmunoassay for serum ursodeoxycholic conjugates using a 125iodine ligand has been developed. The bile acid was present in normal fasting serum (0.19 +/- SD 0.19 mumol/l, n = 24) and 2-hour post-prandial serum (0.8 +/- SD 0.8 mumol/l, n = 16). Gallstone patients undergoing oral ursodeoxycholic acid therapy had significantly higher post-prandial serum levels (21.5 +/- SD 14.0 mumol/l, n = 15) by radioimmunoassay. Gas liquid chromatography analysis indicated that in normal serum ursodeoxycholic acid was totally conjugated, whereas sera from gallstone patients contained a proportion as the free bile acid (10.2 +/- SD 8.1 mumol/l, n = 15). Following an oral dose of ursodeoxycholic acid, both unconjugated and conjugated forms of the bile acid appeared in the serum of healthy individuals.