Radioimmunoassay for the Middle Region of Human Parathyroid Hormone: Studies with a Radioiodinated Synthetic Peptide*

Abstract

We radioiodinated a synthetic fragment representing residues 44-68 from the middle region of human parathyroid hormone (hPTH). At least 90% of the purified [125I]-hPTH-(44-68) was able to bind to anti-hPTH serum. Antibody-bound [125I]hPTH-(44-68) could be rapidly and efficiently separated from nonbound radioligand by dextran-coated charcoal. [125I]hPTH-(44-68) was not degraded after a 72-h incubation in undiluted plasma at 7 C, and it was stable for many weeks at -20 C in a 1% albumin buffer. [125I]hPTH-(44-68) was used to develop midregion specific PTH RIAs. The immunoreactive PTH concentration in plasma was above the upper limit of the normal range in 39 of 43 patients with primary hyperparathyroidism. Values from the midregion assay and an established carboxy-terminus assay correlated using peripheral plasma from 17 patients with primary hyperparathyroidism (r = 0.84; P less than 0.0001) or using parathyroid gland venous effluent plasma from the same 17 patients (r = 0.79; P less than 0.0005). Gel filtration analysis of peripheral plasma from 2 patients with primary hyperparathyroidism and azotemia suggested peptides possessing midregion immunoreactivity but deficient in carboxyterminus immunoreactivity. Similar peptides were present at higher concentrations in parathyroid gland venous effluent plasma than in peripheral plasma, indicating release from the parathyroid gland. In conclusion, [125I]hPTH-(44-68) had properties favorable for the development of RIAs reactive solely with the midregion of PTH. Fragments secreted in vivo by two human parathyroid glands were reactive in midregion assays but nonreactive in a carboxy-terminus assay.

Urinary calcium excretion in familial hypocalciuric hypercalcemia. Persistence of relative hypocalciuria after induction of hypoparathyroidism

“…cAMP in urine was measured by radioimmunoassay (10). PTH in plasma was analyzed with a radioimmunoassay specific for the midportion of the molecule, using purified human PTH (hPTH) as standard (15); the normal range was undetectable to 0.24 ng eq hPTH/ml. The detection limit was 0.10 ng eq hPTH/ml and PTH was detectable in plasma from 50% of normal subjects.…”

Development of Hypercalcemic Crisis in a Graves' Hyperthyroid Patient Associated with Central Diabetes Insipidus.

“…Howver, the incidence of hypercalcemia with greater than 12.0 mg/dl, is very low (1-3) because of hypercalciuria due to the decrease in serum PTH level (3,5,6) and the decrease of intestinal calcium absorption due to the decrease in serum 1,25-dihydroxy vitamin D3 [1,25(OH) 2D3] level (5). It has been also known that hypercalcemia induces a nephrogenic diabetes insipidus (DI)-like state (7).…”

Fate of Parathyroid Hormone during Hemodialysis and Ultrafiltration

“…It cannot be excluded that these fragments are present in such low concentrations in peripheral blood that they become detectable only as a conse quence of accumulation in the dialysate. De spite their apparently very small size, they might correspond to the midregion fragments detected by Marx et al [ 12] and by Roos et al [13] (MW 4000) in the plasma of hyperpara thyroid patients. High transmembranc pres sure enhances the appearance of these PTH fragments in the filtrate, and this might ac count for the differences between the PTH fragments found in the plasma filtrate of ure mic patients and those found in the dialysate [10].…”