A recognition system for sex-hormone-binding protein-estradiol complex in human decidual endometrium plasma membranes.

We have studied the specific binding of human serum sex-hormone-binding protein and its complexes with estradiol and testosterone to an enriched membrane fraction isolated from human decidual endometrium. The specific binding of sex-hormone-binding protein to these membranes has been found to be dependent on it being bound with estradiol. When estradiol concentration in the medium is high enough to provide for the saturation of sex-hormone-binding protein with the steroid, the protein exhibits specific binding to the membranes with an apparent equilibrium constant, Kd = (3.5 +/- 2.0) X 10(-12) M. In the absence of estradiol, the binding protein devoid of steroid or complexed with testosterone does not interact with the membranes. At low concentrations of sex-hormone-binding protein and estradiol, when their complex is almost completely dissociated in solution, it can be reconstituted on the membranes with the optimum estradiol to binding protein ratio being 1:1 (mol/mol). It is proposed that, in plasma membranes of the estradiol target cells, there is a recognition system for the sex-hormone-binding protein-estradiol complex which may allow these cells to take up from blood not only free estradiol, but also estradiol complexed with the binding protein.

Placental protein 12 is a decidual protein that binds somatomedin and has an identical N-terminal amino acid sequence with somatomedin-binding protein from human amniotic fluid.

Placental protein 12 (PP12) was originally isolated from term human placenta and adjacent membranes. Recently we found that the site of PP12 synthesis is decidua but not placenta. In this work, the purity of PP12 was first tested by sodium dodecyl sulfate polyacrylamide slab-gel electrophoresis and by reverse phase HPLC, and the N-terminal amino acid sequence of 15 residues was determined by a liquid-phase sequencer. A single amino acid sequence of Ala-Pro-Trp-Gln-Cys-Ala-Pro-Cys-Ser-Ala-Asp-Glu-Leu-Ala-Leu was obtained showing identity to the known N-terminal amino acid sequence of somatomedin-binding protein from human amniotic fluid. Like the latter, PP12 bound somatomedin (insulin-like growth factor I) as demonstrated in gel chromatography by a shift in the elution pattern of [125I]iodo-insulin-like growth factor I after incubation with PP12. These data show that PP12 is a somatomedin-binding protein and extend through previous literature on PP12 the existing knowledge on the physiology and pathophysiology of somatomedin-binding protein(s) in human reproduction and cancer.

Protein secretion by mesometrial and antimesometrial rat decidual tissue: evidence for differential gene expression.

Our recent finding that decidual luteotropin, a PRL-like hormone secreted by the rat decidua, is found primarily in the antimesometrial cells suggests strongly that the synthesis of this hormone may well be an important function of the antimesometrial tissue. The objective of this investigation was, therefore, 1) to determine whether antimesometrial tissue expresses mRNA for and actively secretes a protein(s) with PRL-like activity, and 2) to examine the pattern of protein production by the antimesometrial and mesometrial zones throughout decidual development. RNA obtained from decidual tissue of day 8 pseudopregnant rats was translated in a cell-free system. The translated products were subjected to PRL receptor affinity chromatography in the presence or absence of ovine PRL to assess binding specificity. The eluted 35S-labeled proteins were analyzed by both sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting. A major 28K protein bound specifically to and was eluted from PRL receptor-enriched luteal membranes. This protein also cross-reacted with antibodies to human PRL. To determine where the mRNA for this 28K protein is expressed and whether this protein represents a prohormone, RNA isolated from both antimesometrial and mesometrial tissue was translated in the presence or absence of microsomal membranes. The 28K protein was synthesized specifically by RNA isolated from the antimesometrial zone. No apparent change in the relative mol wt of the 28K protein was observed when translation was performed in the presence of microsomal membranes. To determine whether this protein is a secreted product and to investigate the pattern of protein secretion by the mesometrial and antimesometrial decidua, tissue explants obtained from both zones between days 9-13 of pseudopregnancy were cultured in the presence of [35S]methionine. Antimesometrial tissue secreted one major 28K protein which was capable of binding to PRL receptors on luteal membranes and was immunoprecipitated by antibodies to human PRL, whereas the mesometrial tissue primarily secreted an approximately 180K protein. The overall pattern of protein synthesis and release not only differed between the mesometrial and antimesometrial tissues but also differed with each day of pseudopregnancy. The secretion of several proteins decreased with advancing gestational age, while the secretion of other proteins began abruptly after day 11, coincident with regression of the antimesometrial tissue. In summary, results of this investigation have established that rat decidual tissue synthesizes and selectively secretes proteins, and the specificity and rate of production of these distinct

Immunocytochemical localization of prolactin and relaxin C-peptide in human decidua and placenta.

The production of PRL by the human decidua is generally accepted, but the production of relaxin by this tissue is not. The two hormones were localized in decidual tissue using the avidin-biotin immunoperoxidase procedure with antisera to human PRL and to a synthetic 14-amino acid sequence of the connecting peptide of human relaxin (hCp14). The object of using the hCp14 antiserum was to verify relaxin production by the detection of C-peptide and/or prorelaxin. Cells of the parietal decidua adherent to the fetal membranes stained with both antisera, and immunostaining for both hormones in the same cell was seen. Also, the decidua-like cells of the placental basal plate stained with both antisera. The chorionic cytotrophoblast stained with the antiserum to hCp14, but not the antiserum to human PRL, whereas the placental syncytiotrophoblast stained for PRL and/or human placental lactogen (hPL), but not hCp14. The PRL staining in all tissues was lost when anti-PRL serum absorbed with human placental lactogen (hPL) was used. This finding suggests that the antiserum to PRL could not distinguish between PRL and hPL. It appears, therefore, that the parietal decidua cells and the decidua-like cells of the placental basal plate may be capable of producing both relaxin and PRL, while the syncytiotrophoblast produces hPL and possibly PRL.

Structural and immunological comparison of insulin-like growth factor binding proteins of cerebrospinal and amniotic fluids.

The insulin-like growth factors (IGFs) found in plasma and a variety of other body fluids are complexed to specific binding proteins (BPs). The cDNA for a 25K IGF-BP was recently cloned and sequenced, and the primary structure of the BP deduced. This BP is found in amniotic fluid, decidual tissues, conditioned medium from HepG2 human hepatoma cells, and fetal plasma. An additional small IGF-BP has been identified in human cerebrospinal fluid (CSF). We now demonstrate that the IGF-BP found in CSF is structurally and immunologically distinct from that found in HepG2 conditioned medium. While the latter BP has approximately equal affinities for IGF-I and -II, the CSF BP has a 10- to 20-fold greater affinity for IGF-II. In affinity cross-linking studies under reducing conditions, the CSF BP had an apparent mol wt (Mr) of 32,000, while the HepG2 BP migrated as a doublet, with apparent Mr values of 30,000 and 28,000. On Western ligand blots, CSF BPs migrate as five discrete bands, with the most prominent band at an apparent Mr of 34,000, while HepG2 medium yielded a single band at an apparent Mr of 30,000. A polyclonal antibody developed against the human amniotic fluid BP immunoprecipitated the HepG2 BP and reacted with both the HepG2 and amniotic fluid BPs on Western blots, but failed to react with the CSF BP. These data indicate that the CSF and amniotic fluid/HepG2 BP are structurally and immunologically distinct small IGF-BPs.

Nonreceptor binding of human chorionic gonadotropin (hCG): detection of hCG or a related molecule bound to endometrial tissue during pregnancy using labeled monoclonal antibodies that bind to exposed epitopes on the hormone.

When hCG adsorbs to surfaces, including membranes from tissues that lack specific hCG receptors, it adsorbs with a particular orientation. Some sites on the alpha- and beta-subunits project away from the surface and can be detected with radiolabeled monoclonal antibodies. Other epitopes, which are located on a region on the hormone that presumably contacts the surface, lose their ability to bind antibody. Using antibodies specific for epitopes on hCG which remain exposed and can be detected when the hormone is adsorbed to rat brain homogenates, we found hCG or closely related substances bound to progestational decidual tissues. Immunologically reactive material adsorbed to the decidual tissue increased and decreased in parallel with the serum levels of hCG throughout pregnancy. Binding of labeled monoclonal antibody to substances similar or identical to hCG in other tissues, including placenta and fetal lung, but not red cells, also was identified. Unlike material adsorbed to decidual tissues, receptor-bound hCG was not recognized by any of our alpha-subunit-specific antibodies. This finding suggests either that the adsorbed hormone has a different orientation than receptor-bound hormone or that the adsorbed hormone has dissociated into subunits. These studies represent the first detection of nonreceptor binding of hCG or related molecules to tissues lacking receptors or presumed not to synthesize the hormone. The role of nonreceptor-bound hCG, if any, is unknown. Other than its effects on stimulation of luteal steroidogenesis during early pregnancy, the role of hCG during most of pregnancy has not been determined. Conceivably, the nonreceptor binding we identified is related to a role for hCG in pregnancy that is not associated with an action on the ovarian LH receptor.

Immunohistochemical demonstration of relaxin in the genital tract of pregnant and nonpregnant women.

The biotin-avidin immunoperoxidase staining method and antisera against highly purified porcine relaxin were used to localize relaxin in the genital tract of pregnant and nonpregnant women. Formalin-fixed tissue specimens from normal placenta, decidua, myometrium, vagina, corpus luteum, and Fallopian tubes were studied. In pregnant women, relaxin was found in the placental syncytiotrophoblast, decidua, and corpus luteum. In nonpregnant women, relaxin was identified in the corpus luteum and endometrium in the secretory, but not in the proliferative, phase. Myometrium, cervix, vagina, and Fallopian tubes were negative for relaxin. This is the first report describing relaxin in the nonpregnant corpus luteum, and we also confirm results of an early disputed study claiming that endometrium in the secretory phase contains relaxin. The origin and biological role of human endometrial relaxin remain to be studied.

Indirect immunofluorescent localization of prolactin to the cytoplasm of decidua and trophoblast cells in human placental membranes at term.

An indirect immunofluorescent technique was used to determine the localization of cytoplasmic human PRL (hPRL) in fresh and incubated human placental membranes at term. In both fresh and 8-h incubated samples of amnion, amniochorion decidua, or chorion decidua obtained from three placentas, we found specific reproducible localization of hPRL to the cytoplasm of decidua and trophoblast cells. The decidua cells appeared to be the most intensely fluorescent. No specific hPRL immunofluorescence was noted in the amniotic epithelium of fresh or incubated samples of amnion and amniochorion decidua. These data suggest that the trophoblast decidua cell layer is the site of PRL localization and possibly synthesis in placental membranes at term and may be the origin of amniotic fluid PRL in humans.

Quantitative comparison between biological and immunological activities of prolactin derived from human fetal and maternal sources.

The biological (BA) and immunological (IA) activities of human PRL have been determined in samples of decidual incubation medium, amniotic fluid, and maternal and fetal cord sera obtained from cesarean sections performed at term. PRL from each of the four compartments was assayed using the Nb2 node rat lymphoma cell line and homologous RIA. BA to IA ratios of PRL, when compared within and between compartments, indicate that the BA of PRL from each compartment is equivalent to that of its IA. Thus, the BA of PRL from decidual incubation medium and amniotic fluid was found not to differ from that of pituitary PRL. These data suggest that PRL produced by decidua and found in amniotic fluid is a biologically active hormone.

Relaxin in human decidua.

Relaxin (RLX) has been purified from the ovary of the pregnant pig and rat but not from human tissues. Our study shows that tissue extracts and incubation media of in vitro culture of human decidua contain a substance with relaxin bioactivities: the inhibition of spontaneous uterine contractions and the elongation of the interpubic ligament. After chromatography on Sephadex G-50 the bioactivity was retained in a protein fraction of approximately 6000 daltons mol wt. The yield of RLX from decidua was 15--33.5 GPU/g fresh tissue. This opens the possibility of the isolation and purification of RLX in the human species.

The presence of gonadotropin receptors in nonpregnant human uterus, human placenta, fetal membranes, and decidua.

The possible presence of gonadotropin receptors in nonpregnant human uterus and human fetoplacental unit was investigated by light microscope immunocytochemistry using a monoclonal antibody to rat luteal hCG/LH receptors. The receptor antibody cross-reacted with human and bovine hCG/LH receptors and appears to be directed against the receptor rather than other proteins, including HLA class I antigens. Uterus and fetoplacental unit contained receptor antibody-binding sites, which indicates the presence of hCG/LH receptors. In the endometrium these receptors were present in glandular and luminal epithelial cells as well as in stromal cells. In the myometrium the receptors were detected in circular and elongated myometrial smooth muscle and vascular smooth muscle. Comparison of immunostaining intensities, which indicates the presence of different amounts of receptors, revealed that luminal and glandular epithelial cells contained more receptors than stromal cells. These cells, in turn, contained more receptors than myometrial and vascular smooth muscle. All cells in secretory phase uterine specimens contained more receptors than corresponding cells from the proliferative phase of the cycle. Midpregnancy placenta, amniotic epithelium, chorionic cytotrophoblasts, and decidual cells contained hCG/LH receptors. At term pregnancy, while receptors in fetal membranes and decidua continue to be detected, placental tissues did not show any detectable receptors unless the tissues were pretreated with neuraminidase. This indicated that term pregnancy placenta contain hCG/LH receptors masked by sialic acid residues. Comparison of immunostaining intensities suggested that syncytiotrophoblasts contained more receptors than cytotrophoblasts at midpregnancy; mesenchymal cells or blood vessels contained no detectable receptors. There were more receptors in decidua than in fetal membranes at mid- and term pregnancy. While the amniotic epithelial receptors decreased, the receptors in chorionic cytotrophoblasts and decidual cells increased from mid- to term pregnancy. In summary, hCG/LH receptors were demonstrated in the nonpregnant human uterus, human placenta, fetal membranes, and decidua. This indicates that hCG/LH may directly regulate functions of these tissues by endocrine, autocrine, or paracrine mechanisms.

Inhibition of decidual prolactin release by a decidual peptide.

Conditioned media from cultures of human decidual explants and aqueous extracts of human decidual tissue contain a factor that causes a reversible dose-dependent inhibition of decidual PRL release in vitro. Decidual explants incubated for 30 min in medium containing 50, 100, and 250 micrograms/ml of a dialyzed and lyophilized preparation of decidual conditioned medium (DCM) released 32.4 +/- 2.7%, 70.9 +/- 4.5%, and 100.0%, respectively, less PRL than control explants. DCM, however, had no measurable effect on the synthesis of decidual PRL or the synthesis and release of trichloroacetic acid-precipitable 35S-labeled proteins. The effect was of short duration and completely reversible. The inhibition of decidual PRL release was not due to PRL, since 500 micrograms/ml human pituitary PRL (a PRL concentration 40 times that in the minimal effective dose of DCM) added to the incubation medium of decidual explants had no effect on the synthesis or release of decidual PRL or trichloroacetic acid-precipitable 35S-labeled decidual proteins. The inhibitory activity eluted from Sephadex G-200 with an apparent molecular weight of 38,000-45,000 daltons, was heat labile, was destroyed by treatment with trypsin, and was unaffected by extraction with acetone-ethanol. These results strongly suggest that the release of decidual PRL is under local control, regulated in part by a factor(s) other than PRL that is released by the decidua.

Immunocytochemical localization of relaxin in human decidua and placenta.

Specimens from 20 human term placentas were stained with 4 different antisera produced against porcine relaxin (Rlx) using the avidin-biotin immunoperoxidase procedure. Cells of the parietal decidua adherent to the fetal membranes, cells of the chorionic cytotrophoblast, as well as cells of the placental basal plate consistently stained with all 4 anti-Rlx sera. Occasionally, Rlx was detected in epithelial cells lining the amniotic membrane. The syncytiotrophoblast stained for Rlx in 2 specimens only. This response was seen only in syncytiotrophoblast that lined villi in close proximity to the basal plate. Syncytiotrophoblast of the chorionic villi either did not stain at all or gave very weak positive immunostaining with the anti-Rlx sera in all specimens. No difference was noted in staining patterns among placentas delivered by elective cesarean section or vaginal delivery.

Human relaxin in the amnion, chorion, decidua parietalis, basal plate, and placental trophoblast by immunocytochemistry and northern analysis.

Immunocytochemistry and Northern analysis were used to show that relaxin is a product of intrauterine tissues of pregnancy. In addition, tissues from a patient without ovaries had similar results on both immunocytochemistry and Northern analysis as tissues from intact patients. The parietal decidua was clearly the major source of relaxin within the uterus and the relaxin mRNA (1.2 kilobases) from this tissue was detected with a 48-mer oligonucleotide probe designed to hybridize with both H1 and H2 relaxin gene transcripts. The mRNA isolated from the placental trophoblast was slightly smaller (1.1 kilobases), and the placental basal plate which has both maternal and fetal cells contained relaxin mRNAs of both sizes. Two monoclonal antibodies (Mabs) raised to synthetic human relaxin (H2) gave different patterns of localization in the fetal membranes, decidua and placenta. One Mab (RLX8) stained the chorionic cytotrophoblast in the fetal membranes and all of the cells in the placental basal plate. The other Mab (RLX6) stained the chorionic cytotrophoblast in some instances and selectively stained the decidua-like cells of the placental syncytiotrophoblast, whereas Mab RLX8 failed to detect this relaxin. Tissues obtained after spontaneous labor and delivery contained significantly less relaxin mRNA than tissues obtained at elective cesarean section without labor, but their hormone contents, as judged by immunocytochemistry, were not different. We conclude that the relaxin gene (H2) is expressed in intrauterine tissues, but that expression and hormone synthesis are not ubiquitous. Whether the relaxin gene H1 is expressed has not been determined.

Uterine estrogen receptors are increased by RU486 in late pregnant rhesus macaques but not after spontaneous labor.

Progesterone withdrawal as a mechanism for parturition in primates is controversial. The progesterone antagonist RU486, given in late pregnancy to rhesus monkeys at a dose of 47 mmol/kg.day (20 mg/kg.day), causes an increase in uterine activity, but not the expected increase in amniotic fluid prostaglandins or cervical dilatation. We, therefore, studied the effect of RU486 on estrogen receptor (ER) localization and concentration in reproductive tract tissues in rhesus monkeys during late gestation and after spontaneous labor at term. Distribution of ER in pregnant uterine tissues was studied by immunocytochemical techniques and quantified by a biochemical assay, both of which employed a monoclonal antibody specific for ER. ER was not present in amnion and chorion by immunocytochemical investigation; however, a significant increase in receptor staining was seen in decidua and myometrium after RU486 treatment compared to that in both pregnant control tissues and parturient tissues. Sucrose gradient assay of nuclear (n) and cytosolic (c) ER revealed a low level of ER (expressed as fmol of estradiol bound/mg of DNA) in pregnant and parturient decidua (pregnant: nER = 7.3 +/- 2.4, cER = 17.1 +/- 6.4; parturient, nER = 7.7 +/- 3.1, cER = 16.4 +/- 8.8) and myometrium (pregnant: nER = 21.7 +/- 4.1, cER = 20.8 +/- 5.3; parturient: nER = 30.0 +/- 2.8, cER = 10.7 +/- 6.7). In contrast, tissues collected from RU486-treated animals contained high levels of ER in decidua (nER = 52.3 +/- 16.8, cER = 240.5 +/- 145.3) and myometrium (nER = 77.0 +/- 19.2; cER = 66.5 +/- 31.6). We conclude that 1) the increase in ER in decidua and myometrium after RU486 treatment is the result of a decrease in the inhibitory action of progesterone on ER and documents the progesterone receptor antagonism by RU486 during induced myometrial contractility in late pregnant rhesus monkeys; 2) the absence of ER from amnion and chorion indicates that the normally observed increase in prostaglandin production by rhesus fetal membranes during labor is not mediated by ER; and 3) the absence of a change in the concentration of ER in decidua and myometrium from pregnant control monkeys and those in spontaneous labor indicates that an increase in ER (and, by inference, a withdrawal of receptor-mediated progesterone inhibition) is not part of the normal events in preparation for parturition in primates.

Influence of osmolality and ionic environment on the secretion of prolactin by human decidua in vitro.

The effects of extracellular osmolality and ions on the secretion of prolactin were examined in human decidual explants incubated for 4 h in modified Krebs-Ringer buffer. Explants incubated in media made hypersomotic (280-336 mosM/kg) with sodium, lithium or mannitol or in media made hypo-osmotic (280-224 mosM/kg) by decreasing the sodium concentration secreted the same amount of prolactin as explants incubated in control medium (280 mosM/kg). Explants incubated in calcium-deficient medium secreted 64 +/- 8% (P less than or equal to 0.001) less prolactin than controls (1.65 mmol Ca2+/1). Secretion was restored to control values by the addition of calcium (0.33 mmol/l) or barium (0.5, 1.0 or 2.0 mmol/l) to the medium. Prolactin secretion was unaffected by higher than control extracellular calcium concentrations, calcium ionophore A23187 (10-6, 10-9 mol/l) or lanthanum (0.5, 1.0 or 2.0 mmol/1). Changes in extracellular magnesium (0-20 mmol/l), potassium (0-55 mmol/l) or bicarbonate (0-32 mmol/l) had no effect on prolactin secretion. These results indicate that marked changes in extracellular osmolality and concentrations of sodium, magnesium and bicarbonate have no effects on decidual prolactin secretion. Calcium, however, is essential for the basal secretion of decidual prolactin.

Human 'pregnancy-associated endometrial alpha 1-globulin', an insulin-like growth factor-binding protein: immunohistological localization in the decidua and placenta during pregnancy employing monoclonal antibodies.

We have previously shown that pregnancy-associated endometrial alpha 1-globulin, a small molecular weight insulin-like growth factor-binding protein (IGF-BP), is quantitatively the major secretory protein product of the decidualized endometrium during human pregnancy. In the present study, employing monoclonal antibodies raised against this protein in an immunohistological technique, the cellular localization of the protein has been examined in the decidua and placenta during pregnancy. During the first trimester the protein was principally associated with the decidual cell in the decidualized decidua compacta region of the endometrium with both cytoplasmic and extracellular matrix-associated staining patterns being detected. No extensive staining was observed in the placenta. At term the protein was localized in similar cells in the placental bed and endometrium associated with the amniochorion but not in the placenta. These studies suggest that the decidual cell represents the major source of IGF-BP during pregnancy and have relevance to the origin of amniotic fluid IGF-BP and the paracrine role of the decidual cell in the control of trophoblast growth.

Immunohistochemical localization of relaxin, prolactin and prostaglandin synthase in human amnion, chorion and decidua.

Relaxin, prolactin and prostaglandin synthase were localized by the avidin-biotin immunoglucose oxidase method in human amnion, chorion and decidua. Specimens from ten normal spontaneous deliveries and four elective Caesarean section deliveries with no labour were compared. Relaxin was found more consistently in the cells of the chorionic cytotrophoblast than in the cells of the parietal decidua adherent to the fetal membranes. Only half the tissues after spontaneous delivery contained positive relaxin-stained cells, whereas all the tissues from elective Caesarean sections contained cells positively stained with antiserum to relaxin. In both series of tissues prolactin was localized predominantly in the parietal decidual cells and was very infrequently found in the chorionic cytotrophoblast. Polyclonal antiserum to prostaglandin synthase was used to identify those cells producing prostaglandin in amnion, chorion and decidua. The cells of the amnion and chorion showed positive immunolocalization with no differences between tissues collected before or after labour. Double immunostaining using avidin-biotin immunoperoxidase for prolactin, followed by avidin-biotin immunoglucose oxidase for prostaglandin synthase, produced identical results in the same series of tissues examined with the single-staining method.

Distribution of prostaglandins E2 and F2 alpha within the foetoplacental unit throughout human pregnancy.

The concentrations of prostaglandin E2 and F2 alpha have been measured by radioimmunoassay in portions of cord, placenta, amnion, chorion, decidua and myometrium. The samples were obtained at defined periods of pregnancy, and the results have been compared with those obtained from the analyses of endometrial and myometrial tissue removed from women during the secretory phase of a menstrual cycle. The results showed that during pregnancy the mean concentration of prostaglandin E2 was higher (27-518%) than the corresponding value for prostaglandin F2 alpha in all tissues. At term the concentration of prostaglandin E2 (ng/100 mg wet weight of tissue, mean +/- S.D.) was higher in the umbilical cord (5-54 +/- 0-88), decidua (4-02 +/- 1-78) and myometrium (4-19 +/- 1-06), than in the amnion (2-25 +/- 1-27), chorion (1-64 "/- 0-63) or placenta (1-04 +/- 0-25). During labour there was a significant rise (P less than 0.0005, Student's 't' test) in the concentration in decidua (10-76 +/- 4-45), and to a lesser extent (P less than 0-05) in the myometrium (5-84 +/- 2-65) and amnion (4-77 +/- 2-51). The overall concentration in decidua during the first trimester (3-09 +/- 1-02) was significantly lower (P less than 0-005) than in endometrial tissue(16-82 +/- 10-13). The concentration was lower in myometrial tissue from non-pregnant subjects (2-90 +/- 2-21), than in the corresponding tissue removed at term (4-19 +/- 1-06) or during labour 5-84 +/- 2-65). The results for prostaglandin F2 alpha showed a similar pattern, but the values were significantly lower in the umbilical cord, and the percentage changes in concentration in the decidua and myometrium were of a higher magnitude.

Triiodothyronine (T3) nuclear binding sites in human placenta and decidua.

We studied the binding of triiodothyronine (T3) to human placenta and decidua. Although the placenta effectively blocks transfer of thyroxine (T4) and T3 it may itself be a thyroid hormone-dependent tissue and may specifically bind T3. A single class of high-affinity binding sites was found (Ka 3.8 +/- 0.31 s.e.m., and 3.3 +/- 10(9) M-1) for both placenta and decidua. Limited capacity was also observed, viz., 0.117 +/- 0.01 and 0.102 +/- 0.018 fmoles/microgram deoxyribonucleic acid (DNA), respectively. Endogenous T3 nuclear saturation was 34 per cent. Our results are consistent with the proposal that placenta and decidua have similar T3 specific nuclear binding sites and that T3 may have a direct action in the placenta.