Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 11, 1996
Publication Date: N/A
Interpretive Summary: A variety of nutrients are transported to the developing pig fetus via proteins secreted by the pig uterus during pregnancy. Factors which increase secretion of these proteins could increase uterine capacity and litter size in swine. By day 60 of pregnancy, the presence of the fetus stimulates uterine protein production. It has been suggested that this occurs due to estrogen secretion by the placenta. The effect of administering estrogens on uterine secretion of proteins during this period of pregnancy (where the fetus is present) or pseudopregnancy (a physiological state similar to pregnancy but in which the fetus is not present) was tested in this experiment. Uterine secretion of total protein, uteroferrin (an iron transporter) or retinol binding protein (Vitamin A transporter) was measured. The presence of the fetus was associated with increases in all three measures of uterine protein secretion and estrogen treatment did not mimic this effect. Therefore, estrogens do not appear to account for the effect of the presence of the fetus on uterine protein secretion. This suggests that other factors from the fetus and/or placenta which stimulate uterine protein secretion are likely to exist. Elucidation of the fetal/placental factors responsible could allow their use in stimulating uterine function, possibly increasing uterine capacity and therefore litter size in swine.
Technical Abstract: The effect of estrone and estradiol treatment from d 30 to 60 of pregnancy or pseudopregnancy on endometrial protein secretion was investigated. Pregnant (P; n=16) and pseudopregnant (PP) gilts (n=18) received either sham treatment or estrone or estradiol implants (5 mg/d release rate; 60 d release) on d 30 of P or PP. Blood samples were collected on d 30, 40, 50, and 60 to measure estrone and estradiol. On d 60, gilts were surgically hysterectomized. For P gilts, endometrium adjacent to one placenta from each uterine horn was collected. For PP gilts, each uterine horn was flushed with 40 mL leucine deficient minimal essential medium (MEM) and endometrial tissue was collected from each horn. Endometrial tissues were incubated in MEM in the presence of 50 uCi [3H]leucine to examine protein secretion. Estrone and estradiol treatments increased both plasma and endometrial concentrations of estrone (P<.01 except endometrium for PP gilts) and estradiol (P<.01, respectively). Endometrium from P gilts secreted more nondialyzable macromolecules (NDM), acid phosphatase activity (AP, a measure of uteroferrin), and retinol binding protein (RBP) in culture compared to endometrium from PP gilts. Estrone treatment increased (P<.01) endometrial NDM from P gilts but not PP gilts; estradiol had no effect. Both estrone and estradiol increased (P=.069) endometrial secretion of AP of PP but not P gilts. Endometrial secretion of RBP was unaffected by either estrone or estradiol treatment. Neither estrone nor estradiol affected total protein or AP and estrone treatment decreased (P<.05) RBP in uterine flushings from PP gilts. These data confirm that the presence of the conceptus is associated with increased endometrial protein secretion but neither estrone nor estradiol completely mimics this effect.