Prolactin Production by the Endometrium of Early Human Pregnancy*

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Abstract
PRL production by the decidualized endometrium of early pregnancy was investigated. Endometrium associated with trophoblast (n = 31) was obtained during therapeutic abortions performed 2–6 weeks post conception. Endometrium free of trophoblast (n = 4) was obtained from the uterine cavity immediately after the surgical removal of ectopic pregnancies in which the blastocyst had implanted within the distal portion of a Fallopian tube. When samples of these tissues were incubated in oxygenated Gey's buffer supplemented with 5% fetal calf serum, the concentration of PRL in the medium increased progressively. After 24 h, the total hormone content of the tissue plus medium was significantly greater than the initial hormone content of the tissue before incubation. When protein synthesis was inhibited by the addition of 50 μg/ml cycloheximide to the medium, the amount of PRL produced during incubation was markedly reduced. The four samples of endometrium which contained no tissue of fetal origin due to tubal implantation were compared to those (n = 5) from intrauterine pregnancies of a similar gestational age (> weeks post conception). No significant differences were found with respect to either initial hormone content or the amount of PRL produced during incubation. Endometria dated as less than 2 weeks post conception (n = 11) contained less PRL initially and, upon incubation, produced less PRL than did the tissues associated with either tubal or intrauterine pregnancies at more advanced stages of gestation. Even less PRL was produced by samples of decidualized endometrium obtained on days 26–27 of normal, nonconceptional menstrual cycles (n = 6); however, nonpregnant endometrium in which the decidual reaction was widespread (days 28–1) contained and produced PRL in concentrations comparable to early pregnancy endometria. These data indicate that human endometrium is competent to produce immunoreactive PRL during the final days of the normal menstrual cycle and that, in a fertile cycle, the capacity for PRL production increases rapidly as implantation progresses. The presence of intrauterine trophoblastic tissue does not appear to be necessary for this process.