2-SITE IMMUNOFLUOROMETRIC ASSAY OF INTACT SALMON-CALCITONIN WITH IMPROVED SENSITIVITY

We recently developed a two-site immunofluorometric assay (IFMA) of sa lmon calcitonin (SCT) by DELFIA (dissociation enhancement lanthanide f luoroimmunoassay) technique using the same polyclonal antibodies both for ''catching'' the antigen and for signaling. In the present study w e used a monoclonal antibody to SCT 1-11 as the capture antibody. This antibody was biotinylated before use in streptavidin-coated microtitr ation plates. The polyclonal antibody labeled with Eu chelate was used as a signaling marker. This combination of antibodies resulted in an assay that was three to four times more sensitive than the previous IF MA, with a detection limit of 0.3 pmol/L serum. Intact SCT 1-32 was de tected by the assay (recoveries 94-96%), but not the fragments SCT 1-1 1 and SCT 10-32 or human calcitonin. Dilutions of plasma samples conta ining SCT were parallel to the calibration curve of SCT 1-32. Pharmaco kinetic studies of SCT, 100 IU administered intramuscularly to 10 men, indicated peak serum concentrations of 32-128 pmol/L within 10-20 min with apparent half-life of 56 +/- 18 min (mean +/- SD). This new assa y will allow study of the pharmacokinetics of new calcitonin preparati ons that do not require injection.