Ovulation-associated increase in intestinal calcium absorption during the rat estrous cycle is blunted by ovariectomy

Intestinal calcium (Ca) absorption was measured under noninvasive conditions in both normally cycling and ovariectomized rats by determining the decrease in 47Ca/47Sc ratio between diet and feces. In 32-wk-old rats fed a 1.4% Ca diet, both fractional and total intestinal Ca absorption varied during the estrous cycle (p < 0.03), being highest during estrus and lowest during the second day of diestrus. Similarly, in 36-wk-old rats fed a 0.11% Ca diet, both fractional and total intestinal Ca absorption varied during the estrous cycle (p < 0.001), being highest during estrus and lowest during the first day of diestrus. In both studies, Ca absorption in ovariectomized rats was identical to the mean values for all of the cycling rats. Serum zinc (Zn) levels, but not those of Ca, phosphorus (P), and magnesium (Mg), varied during the estrous cycle when measured in 37-wk-old rats fed the 0.11% Ca diet.