Radioimmunoassay of conjugated cholyl bile acids in serum.

Abstract

A rapid, sensitive, specific, and valid radioimmunoassay for conjugated cholyl bile acids has been developed. It uses antiserum, produced in rabbits, to cholylglycine coupled by amide linkage to bovine serum albumin. In a radioimmunoassay system, [3H]cholylglycine and antibody reached equilibrium in 1 hr at 42 C. Bound antigen was precipitated by polyethylene glycol, and the free antigen in the supernate was determined by liquid scintillation spectrometry. The displacement curve was linear when the percentage binding of tracer was plotted against logarithmic increase of unlabeled cholylglycine from 5 to 80 pmoles. The antibody bound cholylglycine and cholyltaurine similarly but showed much less affinity for conjugated dihydroxy bile acids or unconjugated bile acids. Cholesterol and hormonal steroids were not bound. The final assay method used less than 0.1 ml of serum and was validated by showing close agreement between radioimmunoassay values and those determined by gas liquid chromatography. In 40 fasting normal subjects, serum levels of immunoreactive conjugated cholyl bile acids were less than 1 μΜ (0.54 ± 0.04 μΜ, mean ± se ). This method should be useful for assessing hepatic function in health and disease.