PTH increases renal 25(OH)D3-1alpha -hydroxylase (CYP1alpha) mRNA but not renal 1,25(OH)2D3 production in adult rats.

The capacity of parathyroid hormone (PTH) to stimulate renal 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] production declines with age in the rat. The purpose of these studies was to determine whether this decline is due to a decreased capacity of PTH to increase the mRNA levels of CYP1alpha, the cytochrome P-450 component of the 25(OH)D(3)-1alpha-hydroxylase. Young (2 mo) and adult (12 mo) male Fischer 344 rats were parathyroidectomized (PTX).

Hormonal regulation of 25-hydroxyvitamin D3-1alpha-hydroxylase and 24-hydroxylase gene transcription in opossum kidney cells.

In the kidney, 25-hydroxyvitamin D(3) (25(OH)D) is converted to 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D) by the 25(OH)D(3)-1alpha-hydroxylase enzyme, which contains a terminal cytochrome P450 (CYP1alpha) (systematic name: CYP27B1). Likewise, the kidney also produces 24,25-dihydroxyvitamin D(3) and 1,24,25-trihydroxyvitamin D(3) via a 24-hydroxylase whose terminal cytochrome P450 is CYP24. The purpose of this study was to characterize the transcriptional regulation of the CYP1alpha and CYP24 genes by parathyroid hormone (PTH) and 1,25(OH)(2)D in the kidney.

Differences in intestinal calcium and phosphate transport between low and high bone density mice.

The purpose of this study was to determine whether there are differences in intestinal Ca and phosphate transport in mice having different peak bone densities. Intestinal transport was measured in C57BL/6 (C57, low bone density) and C3H/He (C3H, high bone density) female mice. Unidirectional (mucosal to serosal) transport of Ca was 58% higher in C3H compared with C57 mice, as measured by everted duodenal sacs.

Differential responsiveness of intestinal epithelial cells to 1,25-dihydroxyvitamin D3--role of protein kinase C.

Non-transformed rat intestinal epithelial cell (IEC) lines were used to study the action of 1,25-dihydroxyvitamin D(3) (1,25(OH)2D) in the intestine. The capacity of 1,25(OH)2D to increase the expression of the cytochrome P450 component of the vitamin D 24-hydroxylase (CYP24) was determined in IEC-6 and IEC-18 cell lines. In IEC-6 cells, which are derived from crypt cells isolated from the whole small intestine, 1,25(OH)2D markedly increased expression of CYP24 protein and mRNA within 12 h.

Capacity of a low calcium diet to induce the renal vitamin D 1a-hydroxylase is decreased in adult rats.

Young animals adapt to a low calcium diet by increasing renal production of 1,25-dihydroxyvitamin D [1,25(OH)2D], the active metabolite of vitamin D. However, the capacity of adult animals to adapt is markedly diminished. With the recent cloning of the cytochrome P450 component (CYP1a) of the renal 1-hydroxylase enzyme complex, it is now possible to determine directly the effect of dietary calcium and maturation on the expression of renal 1-hydroxylase.