Enzyme immunoassay for elcatonin, a synthetic analogue of eel calcitonin, in plasma.

An enzyme immunoassay for the direct measurement of elcatonin, a synthetic analogue of eel calcitonin with hypocalcemic activity, in rat and dog plasma was developed. Elcatonin was conjugated to beta-galactosidase using an N-succinimidyl ester, and the product was used as the tracer. The antibody-bound tracer was precipitated using a second antibody. The nonequilibrated procedure gave better sensitivity and precision than the equilibrated procedure. The nonequilibrated method was sensitive at quantifiable concentrations as low as 0.2 ng/mL using 0.1 mL of plasma and was also reproducible, with RSD values generally less than +/- 10%. Plasma levels in rats and dogs were determined by this competitive enzyme immunoassay after intramuscular or intravenous injection of 40 U/kg (8 micrograms/kg) of elcatonin.