Expression of calcium-sensing receptor and characterization of intracellular signaling in human pituitary adenomas

Extracellular Ca2+-sensing receptor (CaSR) has been recently identified in rat and mouse pituitary and in AtT-20 cells. The aim of the study was to in vestigate the presence of CaSR in the human pituitary and its signaling pat hway. Normal parathyroid biopsies, autoptic normal pituitaries, and seven n onfunctioning and six GH-secreting adenomas were studied. Southern blot ana lysis of the RT-PCR products from pituitary adenomas indicated that the PCR fragments obtained were products of specific amplification of CaSR messeng er ribonucleic acid. Sequence analysis showed nucleotide identity of these products with the available human parathyroid CaSR. By immunoblotting analy sis CaSR, was detected in normal and adenomatous pituitary tissues. In all tumors studied, extracellular Ca2+ (2.5 mmol/L) induced a significant incre ase in intracellular Ca2+, mainly due to Ca2+ mobilization (from 82.7 +/- 1 1 to 148 +/- 36 nmol/L; P < 0.001). Similar results were obtained with the CaSR activators gadolinium and neomycin. Moreover, CaSR activators signific antly increased cAMP levels; this effect was not mimicked by other agents a ble to increase intracellular Ca2+, such as TRH. CaSR agonists did not incr ease resting GH secretion in any GH-secreting adenomas, but amplified the G PI response to GHRH. In this study we first demonstrate CaSR expression in the human pituitary and provides evidence for an additional mechanism by wh ich calcium might regulate pituitary cell function.