Development of homologous immunological assays for human parathyroid hormone

Antisera to a trichloroacetic-acid precipitate of human parathyroid hormone (PTH) were produced in goats. Two of these antisera (G36 and G31) were of high affinity, and the bovine and porcine hormones were less reactive. Synthetic peptides containing the amino-terminal region of human PTH reacted with both antisera; the 1--34 peptide (PTH-(1--34)), with the sequence proposed by Niall, Sauer, Jacobs, Keutmann, Segre, O'Riordan, Aurbach & Potts in 1974, was more reactive than that having the sequence proposed by Brewer, Fairwell, Ronan, Sizemore & Arnaud in 1972. The antisera were further characterized with a number of other native and synthetic fragments of human PTH and reacted poorly with fragments from the carboxy-terminal region of the molecule. Since the amino-terminal fragments did not account for all the immunoreactivity, it is assumed that the antisera had some recognition sites for the central part of the molecule. Highly purified human PTH-(1==84) was labelled with 125I and radioimmunoassays were developed using this tracer and antiserum G36. To avoid the problems associated with labelling human PTH with 125I, a labelled antibody assay was developed with G36 and an immunoadsorbent consisting of human PTH-(1--34) (sequence of Niall et al.) coupled to cellulose. A sensitive homologous amino-terminal specific assay was developed in this way.