The effect of 1α-hydroxycholecalciferol on the placental transfer of calcium and phosphate in sheep

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Abstract
1. The calcium and phosphorus concentrations in foetal tissue or the placental transfer of45Ca and32P, or both, were studied in fifty-five control or 1α-hydroxycholecalciferol (1α-(OH)D3)-treated (0·1 μg/kg body-weight per d for 12 d) ewes between 77 and 140 d of gestation.2. Treatment resulted in a significant increase in the concentration of Ca and P in foetal tissues at all stages of gestation except at 140 d when, it is suggested, foetal mineralization may approach a maximum value.3. This increase in Ca and P concentration in foetal tissues was associated with an increased placental transfer of Ca, though at 111 and 120 d gestation this increase was not significant. P transfer, which was only measured at 140 d gestation, was also significantly higher in treated animals.4. The concentrations of Ca and P in both maternal and foetal plasma were increased significantly by the 1α-(OH)D3treatment.5. Whereas the concentration of Ca in the plasma of foetuses was always greater than in their dams, the concentration of plasma P in treated animals, unlike controls, was lower in foetuses than dams. This suggests that the increased placental transfer of P, unlike that of Ca, may be a passive rather than an active process.