 This is a dose escalation study to determine the maximum tolerable dose of Parathyroid Hormone-related Protein, PTHrP, that can be given safely over one week. The investigators plan to infuse low doses of intravenous PTHrP to determine if it leads to a sustained and progressive suppression of bone formation as occurs in humoral hypercalcemia of malignancy HHM or an increase in bone formation as occurs in hyperparathyroidism HPT. Additionally, the investigators will assess the direct influence of PTHrp on markers of bone turnover, and plasma 1,25 OH2 vitamin D regulation in healthy human volunteers. 