Effect of Intravenous 1-Alpha-Hydroxyvitamin D3 on Secondary Hyperparathyroidism in Chronic Uremic Patients on Maintenance Hemodialysis

Abstract

The effect of intravenous 1.alpha.(OH)D3 on circulating intact parathyroid hormone (PTH) and COOH-terminal immunoreactive PTH was examined in 21 patients on chronic hemodialysis. The patients were treated for 3 months with increasing doses of 1.alpha.(OH)D3 under careful control of serum Ca2+. 1.alpha.(OH)D3 was given intravenously at doses of up to 4 .mu.g three times a week, and blood samples were obtained every week, including 1 week before treatment (basal control). No patients were treated with oral vitamin D metabolites. At the end of the study intact PTH levels were reduced by an average of 67 .+-. 6%, and COOH-terminal immunoreactive PTH levels were reduced by 35 .+-. 6%. Serum Ca2+ was kept within normal levels, but showed a slight increase from 1.17 to 1.30 mmol/l. An effect of calcium on PTH secretion could not be excluded, but an effect of 1.alpha.(OH)D3, independent of serum Ca2+ was also found. This effect may be mediated by 1,25(OH)2D3, assuming a large capacity of the 25-hydroxylase in the liver to convert 1.alpha.(OH)D3 to 1,25(OH)2D3. Also, the parathyroid glands may possess receptors for 1.alpha.(OH)D3 with an effect similar to that established for the 1,25(OH)2D3 receptors. Thus, although the exact mechanisms of the action of 1.alpha.(OH)D3 have not yet been completely clarified, it is concluded that intravenous administration of 1.alpha.(OH)D3 may be of benefit in the treatment of secondary hyperparathyroidism of uremia.