CASR and Hypercalcemia: Recently, we have demonstrated that this relative fetal hypercalcaemia is necessary for optimal prenatal lung fluid secretion10, an effect which is mediated by the extracellular calcium-sensing receptor (CaSR)10, 16, a G protein-coupled receptor (GPCR) whose expression is developmentally regulated and confined to the prenatal mouse and human distal lungs10, 17, 18.