Radioimmunoassay of parathyroid hormone in human plasma and tissue using commercially available antiserum and modified iodination.

The human PTH radioimmunoassay has been developed by use of bovine PTH and anti-bovine PTH antiserum, both of which were commercially available. The iodination process was modified as to use acid solution resulting in the more stable 125I-PTH. However, the PTH radioimmunoassay employed this antiserum with 125I-bovine PTH revealed that the N-terminal portion of PTH molecule was reactive only slightly in this system, indicating that most of PTH determined by this radioimmunoassay might be an biologically inactive PTH. Plasma from normal subjects and patients with primary hyperparathyroidism or uremia showed dilutional curves parallel to the curve of the standard bovine PTH, indicating the immunological identity between human and bovine PTH in this radioimmunoassay system. The extract from the parathyroid adenoma showed an identical dilutional curve, but the extract from the ectopic PTH producing tumor showed a different dilutional curve from that of the standard PTH, which might indicate the immunochemical heterogeneity of PTH produced from the ectopic source. Plasma PTH levels obtained from normal subjects and patients with primary hyperparathyroidism, uremia or pseudohypoparathyroidism were compatible with those reported previously. These data indicate that the human PTH radioimmunoassay can be done by use of commercially available anti-bovine PTH antiserum and bovine PTH in conjunction with the modified iodination process and double antibody method. However, this assay was directed mainly to the C-terminal portion of PTH molecule and the PTH radioimmunoassay specific for the N-terminal portion will be required to evaluate the PTH regulation more precisely in man.