RADIOIMMUNOASSAY OF GANIRELIX IN PLASMA OR SERUM

A procedure for the radioimmunoassay (RIA) of ganirelix in plasma or s erum at concentrations as low as 0.050 ng/ml is described. Antiserum w as produced by coupling the N-terminus glycyl analog of ganirelix to B SA by a carbodiimide reaction and immunizing rabbits with this conjuga te. The antiserum did not crossreact with LHRH or with various ganirel ix peptide fragments. For RIA, I-125 labeled ganirelix was used as the tracer and a double antibody procedure was used to separate the free and bound fractions. No purification of the analyte was required prior to RIA. Accuracy of the method was assessed by adding known quantitie s of ganirelix to ganirelix-free plasma and determining the ratio of m easured to added analyte. Linear regression analysis for the concentra tion range 0.050 - 50.0 ng/ml yielded a regression equation of y = 0.9 7x+0.18, r = 0.999, where x is the amount added and y is the amount me asured. Additional validation was obtained from an in vivo study in wh ich [H-3]-ganirelix was administered to monkeys and plasma clearance p rofiles were determined by RIA and an HPLC-radiochemical method. The r esults were in agreement within experimental error of the two methods. Linear regression analysis of the comparative data gave the equation y = 0.92x + 33.7, r = 0.980, where x is the amount measured by RIA and y is the amount measured by HPLC-radiochemical analysis.