Role of the placenta in intestinal absorption of iron in pregnant rats.

Intestinal uptake (U) and transport (T) of a 40-mug dose of 59Fe from an isolated duodenal loop has been shown to increase from day 15 of pregnancy until term in the rat. U, 60.4 +/- 4.3%, and T, 44.0 +/- 4.6%, were significantly (P less than 0.01) higher than control values, which were 31.6 +/- 3.6% and 18.9 +/- 1.8%, respectively, and resembled those in nonpregnant iron-deficient rats. Eighteen hours before the increase in absorption there was a rapid fall in the t1/2 of 59Fe in maternal serum to 37.2 +/- 3.4 min (control, 72.1 +/- 2.4 min). Hysterectomy at day 20 to 21 of pregnancy resulted in a rise in t1/2 59Fe within 5 hr to 58.0 +/- 4.7%, followed by a fall in U and T to a degree comparable to that in rats studied 18 hr postpartum. Fetectomy had no significant effect on U, 63.8 +/- 2.7%, T, 34.7 +/- 3.4%, or t1/2 59Fe, 27.8 +/- 2.5 min, when compared with corresponding values in day 20 to 21 pregnant rats. The results indicate the importance of placental iron uptake in the control of iron absorption during the 3rd week of pregnancy.