Immunochemical Heterogeneity of Parathyroid Hormone in Plasma

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Abstract
Immunoreactive parathyroid hormone was measured by radioimmunoassay in extracts of parathyroid glands and tumors and in plasmas from patients with 1°, 2° or 3° hyperparathyroidism. On serial dilution most extracts showed approximately parallel behavior in 2 or 3 different antisera. However, plasma specimens referred to the same extract as standard frequently showed greater immunoreactivity in 2 antisera (272 and 273) than in a third antiserum (C329). This anomaly was more marked in plasma from patients with hyperparathyroidism secondary to renal insufficiency than in plasma from patients with 1° hyperparathyroidism and was exhibited by some extracts of adenomas as well. Following parathyroidectomy, the apparent disappearance of parathyroid hormone was more rapid when measured in antiserum C329 than in antiserum 273 and in both antisera was slower in patients with renal insufficiency than in patients with 1° hyperparathyroidism. These findings suggest that parathyroid hormone in human plasma is immunochemically heterogeneous, that removal of one or more of the peptides from the circulation may be dependent on renal function, and that metabolic alteration of the hormone may account for the immunochemical heterogeneity.