An enzyme immunoassay for 6-sulphatoxy-melatonin in human urine.

We describe a newly developed enzyme immunoassay (EIA) for the determination of 6-sulphatoxy-melatonin (aMT6s) in human urine, using a aMT6s-bovine serum albumin-horseradish peroxidase (aMt6s-BSA-HRP) conjugate as the enzyme label. The assay incorporates a highly specific antibody raised in rabbits. The EIA has a sensitivity of 2 pg/well (40 pg/ml) with intraassay coefficients of variation of 2.3-6.1% in the range of the assay. The material with the highest level of cross-reactivity was N-acetyl serotonin sulphate, with a relative potency of 0.000078%. One hundred thirty-four urine samples from children and adults at different time points were assayed and the results compared with those from an established radioimmunoassay (RIA) and with a newly developed RIA using the same antibody as the EIA. The correlation coefficient, r, comparing the two RIA's was 0.9869, and the regression equation was log (kit) = 0.9340 log (new) + 0.1213. The correlation coefficient, r, comparing the EIA with the newly developed RIA, was 0.9686, and regression equation log (new) = 0.9674 log (EIA) + 0.0600. The EIA for the measurement of aMT6s in urine represents a new approach in the investigation of pineal function.