FGF-23 is readily detectable in the plasma or serum of healthy persons and can be markedly elevated in those with oncogenic osteomalacia or X-linked hypophosphatemia, suggesting that this growth factor has a role in phosphate homeostasis. FGF-23 measurements might improve the management of phosphate-wasting disorders.

We have developed a highly sensitive, two-site immunoradiometric assay (IRMA) for human parathyrin (PTH) that is specific for the intact, secreted, biologically active 84-amino-acid peptide. This assay has several technical advantages: it does not detect even high concentrations of inactive carboxyl-terminal fragments, results are available within 24 h, and the detection limit for intact hormone is low (1 ng/L). The assay readily measures concentrations of PTH in all healthy subjects and distinguishes these values from low or undetectable PTH values observed in clinical situations in which PTH secretion is expected to be suppressed. We found complete separation of results from 37 patients with surgically proven hyperparathyroidism and those from 23 patients with hypercalcemia associated with malignancy, the latter having PTH values at or below the lower limits of normal for this assay. The sensitivity, specificity, and rapid turnaround time of this two-site IRMA should advance the laboratory evaluation of patients with disorders of calcium metabolism.

These results indicate that non-(1-84) PTH fragments are composed of a family of fragments which may be generated by specific or progressive cleavage at the N region. The longest fragment starts at position 4 and the shortest at position 15. A peptide starting at position 7 appears as the major component of non-(1-84) PTH fragments. The generation process is similar to the one described for smaller C-PTH fragments a number of years ago, suggesting a similar production mechanism and source for all C-PTH fragments.

Objective: Oncogenic hypophosphatemic osteomalacia (OOM) is a rare disease characterized by hypophosphatemia, inappropriately low levels of circulating 1,25-dihydroxyvitamin D 3 and osteomalacia. The disease is most commonly caused by benign mesenchymal tumors that produce, among several other factors, fibroblast growth factor-23 (FGF-23). Current evidence thus suggests that this protein has an important role in the regulation of phosphate homeostasis. By producing polyclonal antibodies against human FGF-23 protein we wanted to determine the localization of FGF-23 protein in OOM tumors that express FGF-23 mRNA.

Current rat calcitonin immunoassays use human calcitonin antisera, and suffer from poor sensitivity, long incubation periods, nonspecific interferences, and unreliability. The homologous immunoradiometric assay (IRMA) for rat calcitonin described here overcomes these problems. Overnight incubation yields a detection limit of 0.4 pg/mL, a standard curve that is linear to >1800 pg/mL, and intra- and interassay coefficients of variation of <7%. Gel filtration chromatography of rat plasma and rat medullary thyroid carcinoma 44-2 cell media showed that the vast majority of immunoreactivity coeluted with calcitonin standard. In 44-2 cells, increasing extracellular Ca2+ concentration or incubation with the calcimimetic compound NPS R-467 markedly increased calcitonin secretion. Plasma calcitonin levels were elevated in rats anesthetized with ketamine/xylazine and in conscious rats with chronic renal insufficiency. Calcitonin levels decreased following EGTA-induced hypocalcemia and were undetectable after thyroparathyroidectomy. In normal conscious rats, plasma calcitonin levels averaged 3-5 pg/mL and increased up to 100-fold following calcium (Ca) infusion or NPS R-467 administration. The assay also quantified calcitonin in plasma of normal and Ca-injected mice. This assay has revealed that plasma calcitonin levels in normal rats are much lower than the detection limits of most existing assays, but can increase by 100-fold on activation of the C-cell Ca2+ receptor.