Enzyme immunoassay of elcatonin in human plasma.

A sensitive and specific double-antibody enzyme immunoassay (EIA) for detecting an elcatonin-like immunoreactive substance (ECT-IS) in human plasma has been developed. In competitive reactions, the ECT antibody was incubated with a plasma sample (or ECT standard) and beta-D-galactosidase-linked synthetic ECT. Free and antibody-bound enzymes were separated using an anti-rabbit IgG-coated immunoplate. Enzyme activity on the plate was determined by fluorescence analysis. This immunoassay allows the detection of 20 to 300 fmol/ml (67 to 1000 pg/ml) of ECT. The EIA was applied to determine the pharmacokinetic behavior of ECT after a single intramuscular administration (20 IU). The maximum level was achieved 30 min after administration, at approximately 30 pg ECT/ml of plasma.