Abstract
Near term ovine pregnancy is characterized by F:M transplacental plasma gradients of 1,25 [70+7 (F) v 48±4 (M) pg/ml. n=19, p<0.001] and 24,25 [1261±189 (F) v 839±74 (M) pg/ml, n=10, p<0.05]. The relative contributions of placental transfer, placental synthesis and fetal synthesis to fetal plasma levels of these metabolites are presently unclear. To further elucidate the role of fetal synthesis, homogenates of fetal and maternal renal cortex were incubated in vitro with 3H-25 hydroxyvitamin D3 (25 OHD3) to assess 25 OHD3-hydroxylase enzyme activities. Products were identified by co-migration on HPLC with authentic 1,25 and 24,25.All data is expressed as mean ± SEM. The predominant metabolite formed by both fetal and maternal tissue was 1,25. There were no differences between fetal and maternal synthesis rates for either 1,25 or 24,25. However, these synthesis rates, when extrapolated to account for differences in 1) maternal and fetal renal mass and 2) maternal and fetal plasma volume, could wholly account for the fetal plasma levels and transplacental gradients of these metabolites observed in vivo.
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