Primary human trophoblast cells were transfected with VDR siRNA or scrambled siRNA. (A) VDR protein expression in cells transfected with scramble or VDR siRNA, n = 4. System A (B) and System L (C) activity measured in cells transfected with Scramble or VDR siRNA with or without treatment with 1,25-dihydroxy vitamin D3 (1 nM, 24h), n = 6. Data represent mean ± SEM; *P < 0.05; **P < 0.01 vs. control. Scr, scramble; VDR, vitamin D3 receptor; Vit.D is 1,25-dihydroxy vitamin D3.