OF l,25(0H)2-VITAMIN 03 ANO la(OH)-VITAMIN 03

The action of vitamin 0 on the intestinal absorption of phos­ phorus has not been studied extensively in man. Limitations in the use of 32 P labeled phosphate have restricted Observations in large part to those of net absorption derived from metabolic bal­ ance techniques. Using such methods, Stanbury and Lumb (l) and Stanbury (2) reported that pharmacologic doses of vitamin 0 pro­ moted equimolar increments in the net absorption of calcium and phosphorus in patients with advanced renal failure and severe bone disease. Such a relationship between the absorption of calcium and that of phosphorus supports the viewpoint that phosphate transport across the intestine is dependent upon that of calcium. Recent studies in the rat and chick indicate that vitamin 0 or its active forms stimulates intestinal transport of phosphorus independent of an effect on calcium (3,4). In the present study, we have eval­ uated the effect of treatment with 1,25-dihydroxy-vitamin 03 (l ,25 (OH)203) or la-hydroxy-vitamin 03 (la(OH)03) on net absorption of phosphorus in patients with advanced renal failure and normal vol­ unteers. The results in man indicate that both analogs of vitamin 0 enhance the intestinal net absorption of phosphorus.