A homologous radioimmunoassay specific for amino-terminal portion of human
parathyroid hormone(PTH) was developed in order to study the clearance of biologically active species of the
hormone in the circulation in man. Characterization of the assay system with synthetic analogues of human PTH (1-34) indicated that the carboxyl-terminal region of human
PTH(1-34) is an important recognition site. Plasma amino-terminal PTH levels were less than 0.3 ng/ml in all of 35 normal subjects. The levels were elevated above 0.3 ng/ml in 15 of 24 patients with
primary hyperparathyroidism. In 5 patients in whom the levels were determined before and after
parathyroidectomy, the elevated levels were all normalized within 60 minutes after the removal of adenomata. The disappearance of exogenous human
PTH(1-34) was studied after
intravenous administration in 17 patients with
hypoparathyroidism. A graphical analysis of the data disclosed two major components of the disappearance curve with estimated half-disappearance time of 3 and 28 minutes respectively, suggesting that multiple mechanisms are involved in the clearance of the
peptide from the circulation. These results demonstrate usefulness of homologous radioimmunoassay for human
PTH(1-34) in diagnosis and management of
hyperparathyroidism, as well as in studying the clearance of amino-terminal portion of PTH which is known to represent
biological activity.