PARATHYROID-HORMONE SUPPRESSION BY 22-OXACALCITRIOL IN THE SEVERE PARATHYROID HYPERPLASIA

The suppression of parathyroid hormone (PTH) secretion by the administ ration of 1,25-dihydroxyvitamin D [1,25(OH)2D3] and 22-oxacalcitriol ( OCT) was evaluated in nude mice transplanted with human hyperplastic p arathyroid tissue. The parathyroid tissue was obtained for transplanta tion 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. O CT 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 i n 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 w ith normal serum calcium levels as did 1,25(OH)2D3. However, human PTH secretion from the graft was stimulated by the administration of a lo w-calcium diet, despite OCT and 1,25(OH)2D3 administration. In summary , OCT and 1,25(OH)2D3 suppress PTH secretion even from severe secondar y hyperplastic parathyroid tissue only in mice with normal or high cal cium serum levels. (C) 1998, Editrice Kurtis.