A prospective study of 50

A direct immunoassay for circulating intact human PTH (hPTH) is described. The method relies on the formation of an immune complex of labeled antiamino-terminal PTH antibody, intact hPTH, and solid phase antimidregion PTH antibody. A chemiluminescent aryl acridinium ester is used as label. Serum samples (100 microL) are incubated with labeled antibody, and subsequently the bound fraction is separated by the addition of solid phase antibody. The bound luminescence is quantitated in an automatic luminometer. Luminescence intensity is directly proportional to the amount of intact PTH present in the sample. Only intact PTH was found to react in this system; there was no significant interference from PTH fragments. The assay detection limit of 0.8 pmol/L hPTH-(1-84) allowed detection of intact PTH in the serum of all normal subjects tested. A clear distinction was found between hypercalcemic individuals subsequently proven to have primary hyperparathyroidism and those with malignancies. The assay offers several advantages over previously described PTH immunoassays with regard to specificity, rapidity, and reagent stability. It, thus, provides a valuable means of investigating parathyroid physiology and clinical disorders of extracellular calcium metabolism.

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To investigate possible relationships between hyperparathyroidism, alterations in intracellular free calcium concentration ([Ca2+]i) and hypertension in chronic renal failure, serum concentrations of intact parathyroid hormone (PTH) were measured by two-site immunometric assay, and platelet ([Ca2+]i) was assessed using the fluorescent indicator fura-2. Thirty-six patients with chronic renal failure were studied, 10 with normal serum PTH concentrations (mean 8.0 +/- 0.6 pmol/liter), 17 with elevated serum PTH (35.0 +/- 7.2 pmol/liter) and 9 patients with elevated PTH (36.2 +/- 5.9 pmol/liter) who were receiving nifedipine. Platelet [Ca2+]i was increased in patients with elevated PTH, compared with those in whom PTH was normal (138 +/- 16 vs. 83 +/- 7 nmol/liter, P < 0.01). A linear relation was observed between serum PTH and platelet [Ca2+]i in these patients (r = 0.818, P < 0.001). In contrast, platelet [Ca2+]i was not elevated (84 +/- 9 nmol/liter) in the patients with elevated PTH who were receiving nifedipine. A linear relation was also present between both serum PTH (r = 0.616, P < 0.001) and platelet [Ca2+]i (r = 0.576, P < 0.005) and mean blood pressure. Nine patients with hyperparathyroidism were restudied after treatment with the vitamin D analogue alfacalcidol. This resulted in significant decreases in serum PTH (P < 0.01), platelet [Ca2+]i (P < 0.02), and mean blood pressure (P < 0.05). These studies indicate that [Ca2+]i may be increased early in renal failure, and that this increase occurs in association with both hyperparathyroidism and hypertension. Furthermore, treatment of hyperparathyroidism with alfacalcidol may result in reductions in both [Ca2+]i and blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)