Absence of Response to Human Parathyroid Hormone in Athymic Mice Grafted with Human Parathyroid Adenoma, Hyperplasia or Parathyroid Cells Maintained in Culture

In athymic mice we have developed a model of long-term human PTH hypersecretion, using xenotransplantation of respectively parathyroid gland fragments obtained from patients with primary (primary) or secondary (secondary) uremic hyperparathyroidism (HPT), and parathyroid cells maintained in culture from patients with secondary uremic HPT. Both grafted parathyroid tissue fragments and cultured cells induced prolonged and marked secretion of human intact PTH (iPTH) in nude mice. Despite extremely high plasma iPTH levels, hypercalcemia or hypophosphatemia was not observed. Moreover, PTH secretion was not significantly modified by low-calcium, high-phosphate diet for 3 weeks. Four mice which had a mean plasma human iPTH level of 237+/-152 pg/ml for more than 9 months and 4 age-matched, sham-grafted control mice with undetectable human iPTH levels underwent bone histomorphometry examination. No difference was found between the two groups with respect to active bone resorption surface or number of osteoclasts/mm2. We hypothesize that the characteristic deficit of T cell function and of cytokine and growth factor production may protect nude mice with chronic hypersecretion of human PTH from hypercalcemia and bone lesions. We suggest that this strain of mice could be used for better understanding the relationship between cytokines and bone turnover.