OVULATION-ASSOCIATED INCREASE IN INTESTINAL CALCIUM-ABSORPTION DURINGTHE RAT ESTROUS-CYCLE IS BLUNTED BY OVARIECTOMY

Intestinal calcium (Ca) absorption was measured under noninvasive cond itions in both normally cycling and ovariectomized rats by determining the decrease in 47Ca/Sc-47 ratio between diet and feces. In 32-wk-old rats fed a 1.4% Ca diet, both fractional and total intestinal Ca abso rption varied during the estrous cv le (P < 0-03), being highest durin g estrus and lowest during the second day of diestrus. Similarly, in 3 6-wk-old rats fed a 0.11% Ca diet, both fractional and total intestina l Ca absorption varied during the estrous cycle (p < 0.001), being hig hest during estrus and lowest during the first day of diestrus. In bot h studies, Ca absorption in ovariectomized rats was identical to the m ean values for all of the cycling rats. Serum zinc (Zn) levels, but no t those of Ca, phosphorus (P), and magnesium (Mg), varied during the e strous cycle when measured in 37-wk-old rats fed the 0.11% Ca diet.