Influence of pregnancy and the postpartum period on estrogen uptake of the rat fallopian tubes and uterus.

After incubation with 6,7-3H-estradiol, the uptake of radioactivity was measured in rat fallopian tubes and uterus during diestrus, estrus, early and late stages of gestation, and the postpartum period (PP). Uptake patterns during early and late pregnancy reflect the critical endogenous estogenic influence on in vitro hormonal (estrogenic) sensitivity of fallopian tubes and uterus. Very low levels of uptake are observed during the middle and late stages of pregnancy, i.e., day 12 to day 20 postcoitum, followed by a sharp increase during the puerperium (days 1 to 6 PP). However, a close similarity exists between tubal and uterine estrogen uptake patterns during the estrous cycle and critical stages of implantation, followed by pregnancy and the postpartum period.