Determination of proscillaridin in plasma by radioimmunoassay

The development of a sensitive and selective radioimmunoassay for determination of proscillaridin in plasma is described. Antiserum against proscillaridin was obtained from guinea pig immunized with an immunogen prepared by conjugating methylproscillaridin, 14 beta-hydroxy-3 beta-[(4-O-methyl-alpha-L-rhamnosyl)oxy]bufa-4,20,20, 22-trienolid to bovine serum albumin. Methyl N-[3-[(14 beta-hydroxybufa-4,20,22-trienolid-3 beta-yl)oxy-carbonyl] propanoyl]-L-[3',5'-125I2] diiodotyrosinate ([125I] SST) was used as a radioactive ligand. [125I] SST and antiserum were added to the recovered sample from plasma using a Bond Elut column. After overnight incubation, the antibody-bound and free [125I] SST were separated using polyethylene glycol. The mean coefficients of variation of intra and interassay at four different plasma concentrations were 4.0 and 5.0%, respectively. The assay was able to determine as little as 125 pg/ml of proscillaridin in plasma by using 1.5 ml of sample. Beagle dogs were orally administered one tablet (Talusin) containing 0.25 mg of proscillaridin. Proscillaridin was rapidly absorbed, exhibiting plasma maximum concentration of 2.06 ng/ml at 20 min. Thereafter, the plasma level declined biphasically with half-lives of 0.6 and 25.4 h.