Soy isoflavones: no effects on bone mineral content and bone mineral density in healthy, menstruating young adult women after one year.

Background: The effects of isoflavone-enriched soy protein on human bone mineral content (mass) and density in healthy, menstruating young adult females have not been examined in a comparative prospective investigation. Peri- and post-menopausal women have been reported to show beneficial effects of isoflavones on bone measurements. Therefore, young women may also be able to improve their accrual of peak bone mineral content (BMC) and bone mineral density (BMD) during the early adult years of bone consolidation with an isoflavone-enriched diet.

Enhanced nonsaturable calcium transport in the jejunum of rats during lactation, but not during pregnancy.

The lactating (L) rat loses in excess of 100 mg of calcium (Ca) per day to milk at peak lactation. Most of the Ca must be provided by increased intestinal absorption. In an effort to examine adaptation of intestinal calcium absorption during lactation, nonsaturable absorption from the small intestine of rats was calculated from the disappearance of Ca from in situ ligated loops of jejunum during the last week of pregnancy and throughout lactation and weaning.

Regulation of serum calcitriol by serum ionized calcium in rats during pregnancy and lactation.

Serum calcitriol concentrations in rats follow a biphasic pattern during reproduction, with elevated levels during late pregnancy, a decline after parturition, and a rise to even higher levels during peak lactation. We have previously shown that serum calcitriol in rats at peak lactation correlates significantly with, and appears to be regulated by, serum ionized Ca (Ca2+), with parathyroid hormone (PTH) serving a permissive role. We have extended this study by determining if serum calcitriol also correlates with serum Ca2+ during late pregnancy, when calcitriol levels are clearly elevated, and during early lactation, when only modest increases in serum calcitriol are observed.

Altered regulation of parathyroid hormone secretion by calcium in pregnant and lactating rats.

We have previously shown that the serum parathyroid hormone (PTH) concentration in lactating (L) rats is not suppressed by high serum Ca2+ to the same extent as in nonmated (NM) rats. To investigate further Ca2+ regulation of PTH secretion, parathyroid cells from NM rats and rats in late pregnancy and at peak lactation were dispersed and incubated for 2 h in medium containing 0.52-2.

Duodenal active calcium transport in female rats increases with serum calcitriol concentrations, but reaches a plateau far below maximal calcitriol levels.

To determine the relationship between serum calcitriol concentration and duodenal active calcium (Ca) transport, a wide range of circulating calcitriol concentrations (18-950 pg/ml) was obtained by feeding nonmated, lactating, and weaned rats vitamin D-sufficient diets containing 0.04, 0.06, 0.