1. The distribution of 1,25-dihydroxychole-calciferol [1,25-(OH)2D3] receptors in isolated rat jejunal cells was investigated in normal and oophorectomized female rats and also in vitamin D-deficient animals.
2. Oophorectomy caused a selective reduction in 1,25-(OH)2D3 receptor numbers in villous cells, the reduction being similar (37%) in both normal and vitamin D-deficient animals.
3. The data suggest that this effect of oophorectomy reflects a direct effect of oestrogens in the intestinal synthesis of 1,25-(OH)2D3 receptors, independent of the renal synthesis of 1,25-(OH)2D3.
4. It is proposed that this phenomenon may, in part, explain the reduction in calcium absorption which occurs after oophorectomy or the menopause.