Taken together, the absence of a change in bone formation markers and the trend toward a decrease in markers of bone resorption with short-term r-hPRL administration suggest that the increased bone resorption and formation observed in lactation [17] and the increased resorption and decreased formation in patients with hyperprolactinemia from prolactinomas [42] are associated with estrogen deficiency and changes in PTHrP that accompany these physiological states. Here, PRLR is linked to hyperprolactinemia.