Characterization of the molecular forms of immunoreactive parathyroid hormone in primary hyperparathyroidism and in hyperparathyroidism due to renal failure

Abstract

Radioimmunological determination of immunoreactive parathyroid hormone (iPTH) in sera of patients with primary and secondary hyperparathyroidism was carried out using antisera specific for the amino-terminal and the mid-region part of the hormone. In 58 patients with primary hyperparathyroidism and in 29 patients with the secondary form of the disease due to renal failure, there was a linear correlation between the concentration of serum iPTH determined with the two types of antiserum. In all cases the mid-region-specific antiserum measured the highest iPTH concentrations. The molecular forms of serum iPTH were examined after gel filtration of Sephadex G-75 followed by Bio-Gel P-60 in nine patients. Fractions which represented molecular forms equal to or smaller than intact PTH were collected. Using the mid-region-specific antiserum, the predominant immunoreactivity (50–80%) eluted corresponding to one or several large fragments in both forms of the disease. In contrast, iPTH activity co-eluting with the intact hormone represented 2–8% of the total. Similar elution profiles were observed when the amino-terminal-specific radioimmunoassay was used. However, this antiserum showed that in both disease states relatively higher concentrations of iPTH co-eluted with the intact hormone (about 20%).

In conclusion, the higher serum iPTH concentrations measured with mid- region-specific antiserum are mainly due to quantitative differences due to the presence of large and intermediate sized fragments. The appearance of higher concentrations of iPTH in secondary hyperparathyroidism may be due to a reduced degradation and/or filtration by the kidney.

Key-words:

• hyperparathyroidism
• parathyroid hormone