The effects of retinoic acid on the growth of mandible and long bone in fetal rats

Timed-pregnant rats were injected with a total of 90 μg of retinoic acid from day 13 until delivery. Other pregnant groups were given either a total of 390 μg of retinol from day 5 or a total of 270 μg of retinol from day 13 until delivery. Although the weight gains and food intake of the dams during gestation showed no difference between groups, the long bones were slightly heavier in pups born from retinoic acid-injected dams. Total collagen content in both mandibles and long bones did not show differences between retinoic acid-and retinol-injected groups, but collagen synthesis in both bones was greatly increased in the retinoic acid-injected groups. Calcium content of the mandible in the retinol-injected group from day 13 of gestation was increased, whereas ⁴⁵Ca uptake of long bone of this group was increased. Retinoic acid, when injected in physiological doses during gestation, may have some effects on the organic phase of bone, long bones being slightly more sensitive to retinoic acid than the mandibles.