The preparation of a highly specific antiserum for the immunoassay of pregnanediol 3 alpha-glucuronide.

Antisera for the radioimmunoassay of pregnanediol glucuronide have in the past been raised against immunogens in which the carboxyl group of the glucuronide has been attached to the protein. Such antisera do not discriminate well between the glucuronide and the unconjugated steroid. In order to increase this discrimination we have synthesized an immunogen in which the triacetoxy methyl ester of pregnanediol glucuronide is attached to the protein by a 6 beta-hemisuccinoxy bridge. This immunogen was then deprotected to expose the glucuronide. In one group of rabbits deprotection was achieved in vivo simply by injecting the immunogen. In a second group the immunogen was selectively hydrolysed prior to immunization. The antisera raised against these immunogens possessed high affinity and discriminated well between the free steroid and the steroid glucuronide.