CYP27B1 and Hypercalcemia: In addition, given the relatively short half-life of calcitriol, this suggests adequate hydroxylation by porcine CYP27B1. To investigate the possibility of a PTH-like protein being secreted from the porcine kidney and leading to increased bone resorption, CTx was assayed and demonstrated bone resorption was decreased in the presence of hypercalcemia, consistent with nearly absent PTH, and suggesting that bone may not be the source of hypercalcemia.