QUANTITATIVE-ANALYSIS OF THE CALCIUM-SENSING RECEPTOR MESSENGER-RNA IN PARATHYROID ADENOMAS

Background. In primary hyperparathyroidism, hypercalcemia fails to sup press adequately secretion of parathyroid hormone by the parathyroid g land, which may result from failure of the cell-surface calcium recept or (CaR) to sense calcium correctly. Quantification of mRNA concentrat ions should provide important information on the role of expression of CaR in primary hyperparathyroidism. Methods, We have developed a quan titative reverse transcriptase-polymerase chain reaction assay with a competitive template (CaR-M). Amplified cDNAs for CaR and CaR-M are qu antified and the concentration of CaR mRNA is determined from the rati o of CaR-M/CaR versus known CaR-M concentrations. Results. In parathyr oid adenomas (n = 12) the CaR mRNA was 19.2 +/- 2.4 (mean +/- SE) fg/n g total RNA (range, 7.4 to 32.8 fg/ng). Extracellular-ionized calcium levels ranged from 1.38 to 1.74 mmol/L (normal, 1.19 to 1.31 mmol/L) a nd parathyroid hormone from 69 to 345 pg/mb (normal, 14 to 65 pg/ml). In spite of the wide variability in CaR expression in the various aden omas, there was no correlation between mRNA and either extracellular i onized calcium (r(2) = 0.013) or parathyroid hormone levels (r(2) = 0. 001). Normal human parathyroid glands gave values of 8.0 and 16.6 fg/n g; whereas normal bovine parathyroid glands had a mean of 20 +/- 0.6 f g/ng (n = 4). Conclusions. There is no apparent relationship between C aR mRNA levels in adenomas and preoperative Ca and PTH levels. Our fin dings suggest that defective Ca sensing in adenomas may involve posttr anslational modification or signal transduction distal to the receptor Our highly sensitive assay for CaR mRNA should prove useful in examin ing further the role of CaR in Ca sensing-in parathyroid tissue.