Relationship between Ca-dependent change of serum PTH and extracellular Ca2+-sensing receptor expression in parathyroid adenoma

Abnormal PTH secretion and cell growth in hyperparathyroid tissues are acco mpanied with reduced expression of Ca2+-sensing receptor (CaR) which plays a key role in Ca-regulated PTH release. In this study,we examined the recep tor expression in parathyroid adenomas using specific anti-CaR antibody and investigated relationship between CaR expression in adenomatous tissues an d parameters of Ca-dependent change of serum PTH. The results show a consid erable variation in the number of CaR positive cells among the adenomatous tissues. Expression of the receptor protein was not related to set-point er ror but was more reduced in the patients with more elevated minimum or base line levels of serum PTH. CaR expression was severely reduced in the patien ts with highly elevated maximum serum PTH, while the receptor expression wa s also decreased in some patients with normal maximum serum PTH. Baseline l evel/maximum level ratio of serum PTH was increased in these patients. In c onclusion, reduced CaR expression is related to abnormality in three parame ters of PTH secretion (minimum serum PTH, maximum serum PTH, and baseline l evel /maximum level ratio of serum PTH) and may contribute to hypersecretio n from parathyroid adenomas.