Evidence for a new kidney-produced hormone, 1,25-dihydroxycholecalciferol, the proposed biologically active form of vitamin D

Abstract

It has been conclusively shown that vitamin D₃(cholecalciferol) must first be metabolized prior to its mediating intestinal calcium transport. The first transformation is conversion of vitamin D₃by the liver to 25-hydroxyvitamin D₃. This compound is then subsequently metabolized by the kidney to 1,25-dihydroxyvitamin D₃. 1,25-Dihydroxyvitamin D₃is over four times as effective as vitamin D₃and more than twice as effective as 25-OH-vitamin D₃in stimulating intestinal calcium transport. Additionally, 1,25-dihydroxyvitamin D₃is highly active in stimulating bone calcium resorption. As such, 1,25-dihydroxyvitamin D₃likely represents the biologically active form of the vitamin in the intestine and bone. The secretion of this steroid by the kidney and its selective accumulation by the target organs supports the concept that this compound should be regarded as a hormonal regulator of calcium metabolism.