EVIDENCE FOR EXTRA-RENAL 1 ALPHA-HYDROXYLATION OF 25-HYDROXYVITAMIN-D3 IN PREGNANCY

The kidneys are thought to be the only organs capable of 1 α-hydroxylation of vitamin D and its metabolites. We have examined the in vivo conversion of 3H-(25,26)-25-hydroxyvitamin D3 (25OHD3) to 3H-(25,26)-1 α,25-dihydroxyvitamin D3 [1α,25(OH)2D3 in vitamin D-deficient, pregnant and nonpregnant rats. As expected, nephrectomy of nonpregnant, vitamin D-deficient rats prevented the conversion of 25OHD3 to 1α,25(OH)2D3. In contrast, nephrectomy of pregnant, vitamin D-deficient rats reduced but did not abolish the formation of 1 α,25(OH)2D3 from its precursor. The identity of the radioactive metabolite formed from 3H-25OHD3 which circulated in nephrectomized, pregnant rats was established as 1α,25(OH)2D3 by comigration with synthetic 1 α,25(OH)2D3 on high-pressure liquid chromatography. The simultaneous absence of 1 α,25(OH)2D3 in the fetal kidneys indicated that the site of 1 α-hydroxylation after nephrectomy of the pregnant rat was probably extrarenal in origin. Two sites of 1 α-hydroxylation of 25OHD3, one renal and the other extra-renal, either fetoplacental or maternal, may exist in the pregnant, vitamin D-deficient rat. Copyright © 1979 AAAS Copyright.