Parathyroid hormone suppression by 22-oxacalcitriol in the severe parathyroid hyperplasia

The suppression of parathyroid hormone (PTH) secretion by the administration of 1,25-dihydroxyvitamin D [1,25(OH)2D3] and 22-oxacalcitriol (OCT) was evaluated in nude mice transplanted with human hyperplastic parathyroid tissue. The parathyroid tissue was obtained for transplantation from a patient with severe secondary hyperparathyroidism who had undergone a parathyroidectomy. Tissue specimens were transplanted into the gluteus muscle of female nude mice. Animals were divided into two groups; one group was fed a normal diet, and the other group was fed a low calcium diet during the administration of OCT and 1,25(OH)2D3. OCT and 1,25(OH)2D3 were intraperitoneally administered two times every week, for a total of eight times. Serum calcium and phosphate levels were significantly higher in the mouse administered 1,25(OH)2D3 than in the mouse administered OCT. Serum alkaline phosphatase activity was elevated similarly in the mouse administered either OCT or 1,25(OH)2D3. OCT strongly suppressed human PTH secretion from the graft in mice with normal serum calcium levels as did 1,25(OH)2D3. However, human PTH secretion from the graft was stimulated by the administration of a low-calcium diet, despite OCT and 1,25(OH)2D3 administration. In summary, OCT and 1,25(OH)2D3 suppress PTH secretion even from severe secondary hyperplastic parathyroid tissue only in mice with normal or high calcium serum levels.