[A radioimmunoassay for plasma parathyroid hormone (PTH) using N-terminal PTH antiserum (author's transl)].

In order to investigate plasma bioactive PTH, we tried to assay the N-terminal portion of PTH by RIA. The antiserum to PTH was prepared by immunizing rabbits with a bovine 1-34 PTH conjugate BSA. A preparation of labeled PTH was radioiodinated by the chloramine-T or lactoperoxidase method. Labeled PTH was purified by means of adsorption by Quso G-32 powder or a sephadex G-50. The separation of the free and bound labeled hormone was performed by the dextran-coated charcoal method. The assay was carried out as follows: 0.2 ml diluted buffer (0.05 M, pH 8.6, veronal buffer), 0.1 ml standard PTH or sample to be tested, and 0.1 ml anti-PTH serum were mixed. After the first incubation at 4 degrees C for 4 days, 0.1 ml labeled PTH were added. After a second incubation at 4 degrees C for 12 hours, the assay tubes were centrifuged at 2,000 rpm for 30 min and the precipitates were counted. Various hypothalamic, pituitary and thyroid hormones did not interfere with the RIA for PTH. A dose response curve was obtained in a range from 100 pg to 5,000 pg per ml of standard PTH in this assay system. The serum immunoreactive PTH in healthy subjects values less than 290 pg per ml.