Vitamin D3 3 beta sulfate has less biological activity than free vitamin D3 during pregnancy in rats.

The biological activities of free (D3) and sulfoconjugated (SD3) vitamin D3 were compared after 6 weeks of oral administration to D-deficient (-D) female rats which were mated in the meantime. Mothers and pups were sacrificed 1-2 days following parturition and mineral and hormonal plasma status was determined in mothers and bone mineral determinations and bone histomorphometric studies performed. In newborns, plasma levels of Ca, P and 25-hydroxyvitamin D (25(OH)D) were measured. After parturition, -D mothers had decreased body weight (BW) as well as decreased plasma levels of Ca, P and 1,25-dihydroxyvitamin D (1,25(OH)2D) associated with undetectable levels of 25(OH)D. Plasma levels of immunoreactive calcitonin and parathormone, by contrast, were higher than in vitamin D-replete (+D) control mothers. Bone histomorphometric analysis showed osteomalacia and secondary hyperparathyroidism in -D mothers. After parturition, -D +SD mothers had reduced BW compared to D-treated mothers and the plasma parameters measured were abnormal. Almost all bone histomorphometric parameters were found to be intermediate between +D and -D groups without reaching values of +D mothers. By contrast, -D +D mothers had most of the bone formation parameters identical to those of +D mothers. However, bone resorption was still higher while plasma levels of P and 25(OH)D remained slightly, but significantly lower than in +D mothers. In pups, plasma Ca in both D3- and SD3-treated groups was similar to values in +D-treated rats. However, pups from SD3-treated mothers still showed plasma levels of P and 25(OH)D lower than in +D pups. In conclusion, treatment with SD3 in -D mother rats significantly improves the biochemical plasma parameters of pups, but complete normalization can be achieved only in the D3-treated group. Our results show that when administered at equal amounts, SD3 has a much lower biological activity than D3 in -D female rats and cannot therefore replace vitamin D3 particularly during pregnancy.