Radioimmunoassay for 4-[(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthyl)carbamoyl]benzoic acid in dog plasma

A specific and sensitive radioimmunoassay (RIA) was developed for 4-[(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthyl)carbamoyl]benzoic acid (Am-80), a benzoylamide derivative possessing retinoid activity, in dog plasma. Antisera were prepared by immunizing rabbits with Am-80 and its haptenic derivative conjugated with bovine serum albumin (BSA) and keyhole limpet hemocyanin. Their properties were investigated by heterologous combination using 125I-labeled tracer. The antisera raised against BSA conjugate showed poor titers and high specificity, while the antisera from the other two conjugates showed high titers and reasonable specificity. The limit of quantification was 0.6 ng/ml, when only 0.005 ml of dog plasma sample was used per assay tube. The within- and between-assay variances were 1.2-15.0% and 4.0-14.1%, respectively. The direct RIA established here was highly specific for the determination of the unchanged form of Am-80 in dog plasma, enabling measurement of many samples at the same time. (author)