Biologic activity of 3β-D-glucopyranosides of vitamin D compounds

Polar glycosidic conjugates of vitamin D compounds occur in the vegetable and possibly in the animal kingdom. The biologic activity of these conjugates has been examined systematically. To obtain more information on the biological role of such sterol conjugates, we examined the biological activity of the 3β-D-glucopyranosyl conjugates of vitamin D₃ 5, 25-hydroxyvitamin D₃ 6, 1α-hydroxyvitamin D₃ 7 and 1α,25-dihyroxyvitamin D₃ 8. When these compounds were administered i.v. we found that a dose of between 50 and 500 pmol/rat of the four glucopyranosides tested increased active intestinal calcium transport and increased bone calcium mobilization in vitamin D-deficient rats fed a low calcium diet. Under the same conditions, corresponding doses of the parent vitamin D₃ compounds elicited comparable increases in both intestinal calcium transport and bone calcium mobilization. When these compounds were administered p.o. 3β-D-glucopyranosyl vitamin D₃ 5 exhibited no biological activity at doses of up to 5000 pmole/rat, whereas the corresponding glycosides of 25-hydroxyvitamin D₃ 6, 1α-hydroxyvitamin D₃ 7 and 1,25-dihydroxyvitamin D₃ 8 were active at doses of 500 to 1000 pmol/rat in the intestinal calcium transport system. When the glucopyranosyl conjugates were administered i.v. to vitamin D-deficient rats, 25-hydroxyvitamin D₃ and 1α,-25-dihydroxyvitamin D₃ were detected in the serum at levels less than or equal to those noted in animals dosed with the respective free sterols.