A COMPARISON OF THE PHYSIOLOGICAL EFFECTS OF DIHYDROTACHYSTEROL AND VITAMIN D IN THE RACHITIC AND NORMAL DOG

Abstract

The effects of vit. D2 and dihydrotachysterol upon the rate of renal tubular reabsorption of phosphate (phosphate Tm) and the conc. of P and Ca in the serum were studied in rachitic and normal dogs. The phosphate Tm was obtained by detn. of creatinine and phosphate clearances following the intraven. inj. of a 0.1 M soln. of phosphate. . In the normal dog which had received adequate amts. of vit. D, the adm. of dihydrotachysterol resulted in an increase of phosphate Tm and a rise in the concs. of phosphate and Ca in the serum. When dihydrotachysterol was given to the rachitic dog, however, the phosphate Tm was not increased but might drop considerably with a corresponding fall in the serum P. The serum Ca might remain unchanged or rise somewhat if very large amts. of dihydrotachysterol were given. In the normal or rachitic dog vit. D always produced an immediate increase in phosphate Tm with an associated increase in the conc. of phosphate in the serum as well as a rise in the conc. of Ca. The results indicate that although the effects of dihydrotachysterol are similar to those of vit. D in the normal dog, dihydrotachysterol can not substitute for vit. D in the rachitic dog.