Baboon Placenta Research Articles

Developmental expression of the mRNA and protein levels of cytosolic and secretory phospholipases A in the baboon placenta

Developmental expression of the mRNA and protein levels of cytosolic and secretory phospholipases A in the baboon placenta

Comparative localization of endothelial and inducible nitric oxide synthase isoforms in haemochorial and epitheliochorial placentae

The presence and immunolocalization of type II (inducible or macrophage) and type III (endothelial) nitric oxide synthase (NOS) isoforms were compared in the term placentae of humans, rhesus monkeys, baboons, guinea-pigs, rats and sheep using isoform specific antibodies. In the human placenta, intense immunohistochemical staining for type III NOS was seen in syncytiotrophoblast with weaker staining in vascular endothelial cells. Only vascular endothelial cells showed positive type III NOS staining in rhesus monkey, baboon, guinea-pig, rat and sheep placentae. No positive type III NOS immunostaining was seen in trophoblast from any non-human placentae. Western blotting revealed a 135-kDa type III NOS species in placental homogenates, semi-purified by ADP-sepharose affinity chromatography, from all the species tested confirming antibody specificity. Type II NOS immunostaining was localized to certain villous stromal cells which also stained for CD14 (a monocyte/macrophage marker) in the placenta of humans, rhesus monkeys, baboons and sheep. No specific immunohistochemical staining for type II NOS or CD14 was noted in the two rodent species, guinea-pig and rat. On Western blots, a 130-kDa type II NOS species was identified in semi-purified placental homogenates of every species except guinea-pig, although weak bands were seen for rhesus monkey and baboon. The failure of the antibodies to show type II NOS in the rat placenta by immunohistochemistry may be due to a difference in antigen conformation from Western blots. As only human placental syncytiotrophoblast expresses type III NOS, the putative functions ascribed to this isoform in syncytiotrophoblast, i.e. to prevent platelet and leucocyte aggregation in the intervillous space and adhesion to the trophoblast surface or to mediate peptide hormone release from trophoblast, may be unique to humans. Alternatively, syncytiotrophoblast-derived NO may fulfil some other unknown function. The similar pattern of expression of type II NOS in those species with villous fetomaternal interdigitation and multivillous fetomaternal blood flow interrelations may represent a more universal role in surveillance and/or protection against maternal insults or pathogens by immunologic activation and subsequent synthesis of nitric oxide which exerts a cytostatic/cytotoxic response.

The baboon as a nonhuman primate model for assessing the effects of maternal immunization with Haemophilus influenzae type b polysaccharide vaccines.

These studies were performed to assess the utility of the baboon as a nonhuman primate model to evaluate vaccines for use in humans. Specifically, we examined the antibody response of baboons immunized during the third trimester of pregnancy with Haemophilus influenzae type b (Hib) polyribosylribitol phosphate (PRP) conjugate and unconjugated polysaccharide vaccines. Some of the vaccinated mothers failed to respond to a single immunization with unconjugated Hib PRP. Specific Hib PRP immunoglobulin G (IgG) but not IgM antibodies cross the baboon placenta and are detected in the offspring. Higher-titer baboon anti-Hib PRP did not express two previously defined cross-reactive human anti-Hib PRP idiotypes and was biased towards lambda light-chain expression. Spectrotype analysis indicated that baboon anti-Hib PRP was restricted in heterogeneity and oligoclonal.

Cloning and expression of the 11 β-hydroxysteroid dehydrogenase type 1 gene in the baboon

In the baboon, the 11 β-hydroxysteroid dehydrogenase (11 β-HSD)-catalyzed metabolism of maternal cortisol and cortisone by the placenta is an important component in the sequence of events regulating the function of the fetal pituitary-adrenocortical axis. The present study was designed to isolate and sequence the promoter region of the baboon 11 β-HSD-1 gene. The 11 β-HSD-1 genomic DNA was isolated from a baboon kidney genomic library using a human 11 β-HSD-1 cDNA as a probe. The sequence of a 1.7 kb fragment of the 5′-flanking region showed extensive homology (>95) to that published by others for human 11 β-HSD-1 particularly in exons I and II (>95%) and in the proximal promoter (>98%). Using total RNA from adult baboon liver annealed with a 22 bp antisense primer located at the 3′ end of Exon I, parallel genomic sequencing reactions with the same primer confirmed that the baboon 11 β-HSD-1 gene has two transcriptional start sites 93 nucleotides apart and that both start sites are preceded by a CAAT box but not a TATA box. RNase protection assays confirmed that both transcription start sites are utilized in liver and near term baboon placenta and that transcripts emanating from the downstream start site dominate in the placenta in contrast to the preferential utilization of the upstream start site in adult liver.

Developmental increase in expression of the messenger ribonucleic acid and protein levels of 11beta-hydroxysteroid dehydrogenase types 1 and 2 in the baboon placenta.

Cortisol-cortisone interconversion is catalyzed by the NADP/NADPH-dependent oxido-reductase, 11beta-hydroxysteroid dehydrogenase-1 (11betaHSD-1) and the NAD-dependent oxidase, 11betaHSD-2. Because of the importance of placental corticosteroid metabolism in dictating the amount of cortisol arriving in the fetus to regulate fetal pituitary-adrenocortical function, the present study determined whether there was a developmental change in the expression of 11betaHSD-1 and/or -2 in placental syncytiotrophoblast, the site of maternal:fetal exchange. A syncytiotrophoblast-enriched (>95%) cell fraction was isolated from baboon placentas obtained at early (day 60), mid (day 100), and late (day 165) gestation (term = day 184), and 11betaHSD-1 and -2 messenger RNA (mRNA) and protein levels were determined by Northern and Western blots. The levels (mean +/- SE) of the single 1.6-kilobase (kb) mRNA for 11betaHSD-1, expressed as a ratio to beta-actin, increased (P < 0.05) between early (0.36 +/- 0.16; n = 4) and mid (0.95 +/- 0.21; n = 11) gestation and further increased (P < 0.05) by late gestation (1.82 +/- 0.29; n = 13). Similarly, the levels of the single 1.9-kb mRNA for 11betaHSD-2 in late gestation (2.46 +/- 0.35; n = 8) were greater (P < 0.05) than respective values at mid (1.36 +/- 0.22; n = 8) and early (0.64; n = 2) gestation. The levels of 11betaHSD-1 (arbitrary densitometric units), detected as a dominant band of 34 kDa, were greater (P < 0.05) in late gestation (2.6 +/- 0.2; n = 4) than at early (1.2 +/- 0.1; n = 4) or mid (1.9 +/- 0.3; n = 4) gestation. In contrast, 11betaHSD-2 was not detected by Western blot in syncytiotrophoblast isolated by collagenase dispersion. However, immunocytochemistry revealed that 11betaHSD-2 was present in and localized to the syncytiotrophoblast layer of the baboon placenta and that expression in late gestation (n = 4) appeared to exceed that in placentas of early (n = 4) and mid (n = 4) gestation. These results indicate that both 11betaHSD-1 and 11betaHSD-2 were expressed in syncytiotrophoblasts of the baboon placenta and that the mRNA and protein levels of these two 11betaHSD enzymes increased with advancing gestation. However, because 11betaHSD-2 was not detected in syncytiotrophoblast isolated by collagenase dispersion, we suggest that the 11betaHSD-1 and -2 reside in different membrane fractions of the syncytiotrophoblast. Consequently, the estrogen-regulated change in transplacental cortisol metabolism with advancing gestation may result in a developmental change in the expression and location of the two 11betaHSD enzymes controlling cortisol-cortisone metabolism and transfer into the fetus, resulting in activation of the fetal pituitary adrenocortical system.

Developmental increase in expression of the messenger ribonucleic acid and protein levels of 11beta-hydroxysteroid dehydrogenase types 1 and 2 in the baboon placenta

Developmental increase in expression of the messenger ribonucleic acid and protein levels of 11beta-hydroxysteroid dehydrogenase types 1 and 2 in the baboon placenta

Interconversion of cortisol and cortisone in the baboon placenta at midgestation: expression of 11beta-hydroxysteroid dehydrogenase type 1 messenger RNA.

At midgestation in the baboon, 11beta-hydroxysteroid dehydrogenase (11beta-HSD) catalysed interconversion of cortisol (F) and cortisone (E) during transuterine passage favors the formation of F. Because the site(s) of oxidation/reduction of F and E are not clear, the present study compared F-E interconversion in placenta, decidua and chorion in vitro. In addition, because the reduction of E to F is catalysed only by the 11beta-HSD-1, we also determined whether the mRNA for this enzyme was expressed in baboon placenta, including placental syncytiotrophoblast cells; the site of fetal-maternal exchange. Placentas were obtained on day 100 of gestation (term = day 184) and villous tissue, decidua and chorion isolated, minced in HBSS and incubated (300-400 mg) in duplicate for 0.1-24 h in Medium 199 containing 10% fetal bovine serum and [3H]F and [14C]E. Radiolabelled F and E were purified from incubates and the percentage conversion of F to E and E to F was calculated. In decidua, mean (+/- SE; n = 3) conversion of E to F (69 +/- 2%) was greater than oxidation of F to E (26 +/- 2%). Conversion of E to F in placenta (50 +/- 1%) and chorion (39 +/- 9%) was also extensive and greater than or equal to that for the oxidation of F to E (39 +/- 4% and 32 +/- 4%, respectively). The apparent ratio of 11beta-HSD reductive/oxidative activity was maintained when respective tissues from four baboons were incubated for 18 h with or without 4.4 microM excess radioinert substrate. Expression of 11beta-HSD-1 mRNA was determined by Northern blot by hybridization of poly (A) + -enriched RNA from tissues obtained at midgestation with [32P]labelled human 11beta-HSD-1 cDNA. This cDNA hybridized to a single mRNA species of 1.6 kb in decidua, whole placental villous tissue and syncytiotrophoblast cells, but not to RNA isolated from fetal baboon kidney. The results of the present study demonstrate that at midgestation in the baboon, 11beta-HSD activity in intact placenta and decidua in vitro favored the formation of F from E, presumably catalysed by the 11beta-HSD-1 enzyme protein, the mRNA for which is present in placental syncytiotrophoblasts. Moreover, based on overall mass and extensive vascularity, we suggest that the net formation of F from E during transuterine passage in vivo at this stage of gestation results from the 11beta-HSD-1 in the syncytiotrophoblast cells of the baboon placenta.

Different molecular and messenger ribonucleic acid forms of insulin-like growth factor-binding protein-3 in the pregnant baboon (Papio anubis)

The ratio of the serum concentrations of insulin-like growth factors (IGF) to IGF-binding protein (IGFBP)-3 is highly correlated (Baxter & Martin 1986). During pregnancy in the baboon, this ratio is perturbed; serum IGFBP-3 concentrations increase 10-fold, yet IGF-I levels are unaltered and IGF-II is increased only 2-fold (Giudice et al. 1993). The aims of this study were to determine the molecular distribution of IGFBP-3 and to identify the tissue source and form(s) of IGFBP-3 during pregnancy in the baboon. Serum of non-pregnant and pregnant baboons, and conditioned media of decidua and placental explant cultures were characterized using neutral size-exclusion chromatography in combination with Western ligand blot, Western immunoblot, an IGFBP-3 radioimmunoassay (RIA) and an IGFBP-3 protease assay. Localization of immunoreactive IGFBP-3 was determined by immunocytochemistry, and expression of IGFBP-3 mRNA in the placental and decidual explants was examined by Northern blot analysis. RIA confirmed that immunoreactive IGFBP-3 is increased 10-fold in pregnancy serum compared with non-pregnancy serum. Size-exclusion chromatography combined with an IGFBP-3 RIA revealed that, unlike non-pregnancy serum where 70% of the immunoreactive IGFBP-3 elutes in the 150 kDa ternary complex, equal amounts of immunoreactive IGFBP-3 were measured in pregnancy serum in the < or = 150 and 60 kDa IGFBP regions. Western analysis revealed that non-pregnancy serum contained predominantly a 45-40 kDa IGFBP-3 doublet and a 28 kDa immunoreactive form of IGFBP-3, while in pregnancy serum IGFBP-3 existed as a 45-40 kDa doublet, as well as 26-28 kDa and 18 kDa immunoreactive forms. These alternative forms of IGFBP-3 were not attributable to detectable IGFBP-3 protease activity. To identify the source of the increased serum levels of IGFBP-3 during pregnancy, we examined explant culture media of baboon decidua and placenta. Size-exclusion chromatography combined with RIA and Western analysis revealed that: (1) more immunoreactive IGFBP-3 was produced by decidual cultures than by placental explants, but less 45-40 kDa IGFBP-3 was present in decidua; (2) the immunoreactive forms of IGFBP-3 detected in decidua were similar to those found in maternal serum; (3) placental explants secreted only 45-40 kDa IGFBP-3 in culture. IGFBP-3 was immunohistochemically localized to the cells of placental villi, and to the perinuclear region of the decidual cells and staining for IGFBP-3 was more intense in the decidua than in the placenta. Northern analysis of the explant cultures revealed two IGFBP-3 mRNA transcripts of 2.4 and 1.7 kb in both decidua and placenta which may account for the different immunoreactive forms of IGFBP-3 detected in the baboon. However analysis of non-pregnancy liver also revealed two IGFBP-3 transcripts of 2.4 and 1.7 kb. These data suggest that the two transcripts are not solely pregnancy-associated and levels of protein may be the reason for detection of multiple immunoreactive IGFBP-3 fragments in pregnancy.

Studies on conversion of labelled pregnenolone to progesterone by olive baboon placental cytotrophoblast cells in vitro

The experiments were designed to study the influence of a variety of substances, which have been reported to affect placental steroid metabolism, on pregnenolone metabolism by olive baboon placenta cells.

Influence of fetectomy on serum pregnancy-associated plasma protein-A concentrations in the baboon.

In baboons as in humans, the placenta is a source of various peptides, including pregnancy-associated plasma protein-A (PAPP-A). However, our present understanding of the regulation of PAPP-A production is incomplete. We have demonstrated that after fetectomy, the baboon placenta retains steroidogenic capacity and is maintained in utero until delivered spontaneously close to term. We have suggested, therefore, that fetectomy provides a valuable in vivo approach to elucidating the role(s) of the fetus, and of the hormones (e.g., estrogen and progesterone) dependent upon the presence of the fetus, in the regulation of placental steroidogenesis during primate pregnancy. Therefore in the present study we utilized the fetectomy model to evaluate the respective roles of the fetus, estrogen, and progesterone on placental PAPP-A. Estradiol, progesterone, and PAPP-A concentrations were determined by RIA in maternal blood collected under ketamine anesthesia on Days 78-100 (n = 5), Days 102-144 (n = 4), and Days 146-164 (n = 3) of gestation (term = Day 184) in control baboons (Papio anubis) and on Days 110-164 in baboons fetectomized on Day 100 (n = 9). Studies were also conducted in five animals in which placental estrogen was increased by maternal treatment on Days 70-100 with androstenedione and in three animals treated on Days 140-164 with the antiestrogen, ethamoxytriphetol (MER-25; 25 mg/day/kg BW).(ABSTRACT TRUNCATED AT 250 WORDS)

Secretory and Morphological Changes in the Baboon (Papio Anubis) Uterus and Placenta during Early Pregnancy1

The study was undertaken to characterize changes in uterine endometrial secretory activity and morphology in the baboon between Days 18 and 32 of pregnancy. Proteins synthesized by the implantation site endometrium (RI) and non-implantation site endometrium (RIII) and developing placenta were analyzed by two-dimensional PAGE and fluorography. The electrophoretic mobility and localization of chorionic gonadotropin (CG) in the baboon placenta, and insulin-like growth factor binding protein-1 (IGFBP-1) and retinol binding protein (RBP) in the baboon uterus were confirmed by Western blot analysis and immunocytochemistry. Placental protein synthesis was primarily characterized by the presence of radiolabeled CG at Days 18 and 25, which decreased by Day 32. Peak CG synthetic activity, immunolocalized to the syncytiotrophoblast, occurred during the formation of tertiary villi. Also associated with the development of mature villi was a corresponding increase in a basic protein (M(r) 23,000). The overall secretory pattern of the baboon endometrium was similar to that observed during the midluteal stage; however, the synthetic activity was enhanced during pregnancy. Radiolabeled and immunoreactive IGFBP-1 and RBP were detectable in the Day 32 functionalis and basalis, respectively, and their synthesis was higher in RI compared to RIII. The immunolocalization of IGFBP-1 in RI appeared to be directly related to the degree of decidualization. In addition, a novel group of low molecular-weight (M(r) 27,000-30,000) isoelectrovariant proteins was secreted predominantly by the basalis at Days 18 and 25 of pregnancy and disappeared by Day 32 in all but one animal. The synthesis of this group of proteins did not show regional specificity. These studies indicate that the baboon endometrium undergoes morphological and secretory changes during pregnancy that are associated with the development of a functional placenta and decidualized endometrium. Furthermore, these studies suggest that the conceptus/placenta may mediate specific changes in IGFBP-1 and RBP expression at the implantation site.

Regulation of insulin-like growth factor-binding proteins in the baboon (Papio anubis) uterus during early pregnancy.

The baboon uterus begins to synthesize insulin-like growth factor-binding protein-1 (IGFBP-1) in the deep glands of the late secretory endometrium, and this protein then becomes the major secretory product of the term decidua. We hypothesized that the placenta and/or conceptus may regulate the synthesis and secretion of IGFBP-1 by decidualized stromal cells during pregnancy. To test this hypothesis, tissue was obtained from pregnant baboons on days 18, 25, and 32 postovulation. The uterus was separated into three regions: RI (directly below the implantation site), RII (adjacent to the implantation site), and RIII (opposite the implantation site). Portions of the tissue were fixed in Bouin's solution for immunocytochemistry, and the remainder was subdivided into functionalis, basalis, and myometrium and subjected to organ explant culture. The placenta was fixed or cultured separately. Ligand blot analysis of functionalis medium showed that the major IGFBP had a mol wt (Mr) of 29,000-31,000; however, a doublet of 37,000-43,000 Mr and a band at 24,000 Mr were also present. The functionalis from all regions expressed the majority of the IGFBPs, but basalis from RI tissue also secreted the same array of IGFBPs on days 25 and 32. Ligand blot analysis of placental medium proteins revealed a doublet at Mr 37,000-43,000 on days 25 and 32, but not on day 18. Immunoprecipitation followed by ligand blot analysis of medium proteins using polyclonal antibodies to IGFBP-1 and IGFBP-2 and -3 confirmed that IGFBP-1 and -2 were the predominant products of the endometrium and decidua, while IGFBP-3 was synthesized by the placenta. Immunocytochemistry with a monoclonal antibody to IGFBP-1 demonstrated intense glandular epithelial staining in all regions on days 18, 25, and 32. Stromal staining for IGFBP-1 was first evident on day 25 and was only present in stromal cells in intimate contact with the trophoblastic tissue. By day 32, IGFBP-1 expression was not limited to the endometrial-trophoblastic junction, but extended to the deeper stromal cells and included the perivascular regions. IGFBP-1 staining was most intense in RI, but stromal cells at the luminal surface and those surrounding the spiral arteries also showed some staining in RII and RIII on day 32. These studies suggest that the baboon placenta and/or conceptus regulate IGFBP expression in the uterine endometrium during the initial stages of pregnancy.(ABSTRACT TRUNCATED AT 400 WORDS)

Scanning electron microscopy of primate chorionic villi following ultrasonic microdissection

Villi from human, macaque and baboon placentae were subjected to ultrasonication after prolonged osmication, and examined by scanning electron microscopy. The technique was often successful in removing the overlying trophoblast and revealing expanses of the trophoblastic basal lamina, a conclusion corroborated by transmission electron microscopy. These preparations bore a remarkable similarity in appearance to microvascular cast preparations of the fetal vasculature. Relatively straight parallel tubules appeared to correspond in position to the location of fetal vessels in intermediate villi, whereas portions of the basal laminae of terminal villi were in the form of convoluted, branched cylinders similar to SEM images of fetal capillaries of terminal villi. The basal lamina did not have evidence of pores as has been described in some basal laminae.

Regulation of 1lβ-Hydroxysteroid Dehydrogenase Activity in the Baboon Placenta by Estrogen*

We have previously shown that the change in transuteroplacental cortisol (F)-cortisone (E) metabolism in vivo from preferential reduction (E to F) at midgestation to oxidation by term (F to E) does not occur in baboons in which the production or action of estrogen have been blocked. Moreover, because the administration of androstenedione (delta 4A) to baboons increased estradiol (E2) production at midgestation and induced a pattern of F-E metabolism similar to that at term, we suggested that estrogen regulates placental F-E interconversion. The present study was designed to ascertain whether estrogen regulates the activity of the placental 11 beta-hydroxysteroid dehydrogenase (11 beta HSD) enzyme catalyzing the oxidation of F to E. Placentas were obtained on day 100 (n = 10) and day 165 (n = 10) of gestation (term = day 184) from untreated baboons, on day 100 from animals (n = 7) treated with delta 4A between days 70-100 of gestation, and on day 165 from animals in which placental estrogen was decreased by fetectomy (n = 5) on day 100 of gestation. Tissue was homogenized in phosphate buffer (pH 7.4) and microsomal fractions (105,000 x g) incubated (37 C; 2 min) in buffer containing 2.7 mM NAD+ and 0.03-1.0 microM [3H]F. Serum concentrations of E2 (nanograms per ml) in untreated baboons on day 100 (0.7 +/- 0.2) were 3-fold lower than those at term, increased (P less than 0.05) by delta 4A treatment (2.4 +/- 0.3), and decreased (0.12 +/- 0.01; P less than 0.05) by fetectomy. The specific activity (picomoles of E per min/mg protein) of placental 11 beta HSD in untreated baboons at midgestation (134 +/- 17) was increased (P less than 0.01) 3-fold by delta 4A treatment. Enzyme activity at term (148 +/- 29) was similar to that at midgestation, but markedly decreased (P less than 0.01) by fetectomy (16 +/- 4). Placental capacity to oxidize F to E (micromoles per min/placenta) in untreated baboons was 3-fold greater (P less than 0.01) at term (88 +/- 15) than at midgestation and was markedly reduced (P less than 0.01) by fetectomy (3 +/- 1). Collectively, these findings indicate that the activity of the placental 11 beta HSD enzyme catalyzing the oxidation of F to E is increased in baboons in which placental estrogen production was elevated at midgestation and decreased in animals when estrogen formation was inhibited by fetectomy.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunohistochemical localization of chorionic gonadotrophin on baboon placenta, dispersed trophoblast cells and those derived from blastocysts grown in vitro

An immunohistochemical technique using a high specificity antiserum against baboon CG was used to demonstrate the presence of a CG-like material on: (1) fixed baboon placental sections collected between 31 and 39 days of gestation, (2) trophoblast monolayers derived from hatched embryos grown in vitro for 15 days and (3) trophoblast cells derived from cells dispersed from placentae collected between Days 31 and 39 of pregnancy. A specific radioimmunoassay was used to detect concentrations of baboon CG in daily spent medium. Immunohistochemical studies showed that material cross-reacting with CG was present on all the three sources of trophoblast. The embryos secreted CG from attachment onwards and immunoactive CG was measurable in daily spent medium collected from placenta-derived trophoblast cultures. It is concluded that baboon CG is localized in the syncytiotrophoblast of fixed placental sections and cellular trophoblast derived from cultured embryos and placental cells.

Characterization of Baboon Pregnancy-Specific α1-Glycoprotein1

Immunostaining of baboon placental tissues with anti-human pregnancy-specific beta 1-glycoprotein (SPI) antibodies demonstrated that an SP1-like molecule was present in the syncytiotrophoblasts. Staining was observed on the membrane and in the cytoplasm, but the nucleus was devoid of any staining. Western blot analysis further demonstrated the presence of five protein species in baboon placental extract, whereas four protein bands were detected in human placental extract. Culture medium of baboon placental villi also contained five SP1-like molecules with sizes slightly different from those present in the placental extract. Amniotic fluid and culture medium of decidua basalis and chorioamniotic tissue contained lesser quantities and fewer species of SP1-like molecules. However, an 87 kDa band was present in all samples examined. Northern blot analysis of baboon placenta with a human placental SP1 cDNA probe demonstrated the presence of a 1.65 Kb band, whereas two hybridizing bands (1.65 Kb and 2.25 Kb) were present in human placenta. Southern blot analysis of baboon genomic DNA further demonstrated the presence of multiple bands hybridizing with a human placental SP1 cDNA probe. These results showed the presence in baboons of multiple genes encoding mRNAs and proteins highly similar to human placental SP1.

A Comparative Evaluation of the Transport of H2-Receptor Antagonists by the Human and Baboon Placenta

Using a single cotyledon perfusion model, the placental transport of four H2-receptor antagonists, cimetidine, famotidine, nizatidine, and ranitidine, was determined and compared using normal term human and normal preterm baboon placentas. In both the human and baboon placentas, the transport of each agent was similar whether administered singly or in combination with the other drugs. Drug transport was the same in both directions, maternal-to-fetal and vice versa, indicating a lack of preferential transfer. The H2-receptor antagonists were transported at about 40% the rate of the freely diffusable reference compound, antipyrine. There were no significant differences between the human and baboon in any of the parameters of placental function evaluated. Placental glucose and oxygen consumptions, and lactate production were comparable in the human and baboon preparations. The transport and clearance of each of the H2-antagonists were similar in each species.

The nucleotide sequences of baboon chorionic gonadotropin β-subunit genes have diverged from the human

The placental glycopeptide hormone chorionic gonadotropin (CG) is involved in establishing and maintaining pregnancy. The hormone consists of two different non-covalently associated subunits termed α and β. In man there are seven closely linked genes coding for βCG-like peptides, but only three of these appear capable of expression in the placenta. The organization of βCG-like genes in man and baboon appears to be similar. We demonstrate here that the baboon genome contains multiple copies (at least five) of βCG-related genes, and that these genes are closely linked in the genome. Nucleotide sequence data from several βCG cDNA clones indicates that at least two of these βCG-related genes are expressed in the baboon placenta. Analysis of βCG sequences from baboons and human subjects demonstrates that these genes have diverged markedly between species. In contrast, these sequences are remarkably homogeneous within their respective genomes. Gene conversion events may be responsible for retaining the high degree of identity among the various βCG gene family members. Knowledge of βCG sequences from baboon may lead to development of a long-term antipregnancy vaccine. The ability of CG antibodies to interfere with the maintenance of pregnancy can now be investigated within a homologous system.

Comparison of cortisol-cortisone interconversion in vitro by the human and baboon placenta

The kinetics of 11 β-hydroxysteroid dehydrogenase (11HSD) catalyzing the interconversion of cortisol (F) and cortisone (E) were compared in vitro following incubation of homogenates of human ( N=7) and baboon ( N=2) placenta. In both species, enzyme activity catalyzing the conversion of F to E was associated with the membrane fraction of the cell, was greater in the presence of NAD+ than NADP+, was of similar concentration within the placenta, and exhibited a similar Km for F. Moreover, there was no conversion of E to F in either the baboon or human placenta indicating that in both species, term placenta lacks the 11HSD enzyme catalyzing the reduction of the 11-oxo group of corticosteroids. Significantly, the conversion of F to E by both the baboon and human placenta was inhibited when progesterone was added to the reaction mixture at concentrations equimolar to the substrate. We conclude that 11HSD enzyme kinetics in term baboon placental homogenates are similar to those measured in human term placenta. Moreover, progesterone may be a physiologic regulator of 11HSD in both the human and baboon placenta. Collectively, our findings support the use of the baboon as a model for studies of the regulation of placental corticosteroid metabolism during human pregnancy.

Immunological studies of transferrin and transferrin receptors of human placental trophoblast

In primate pregnancy, fetal iron is derived from maternal transferrin; however, the mechanisms by which iron is taken up by the human placenta have not yet been established. In the present study, transferrin was demonstrated on the microvillous surface of human trophoblast in immunohistological studies of 130 mature and immature placentae from both normal and abnormal pregnancies. Similar results were found for baboon placentae. Upon short-term culture of placental tissue, the amount of trophoblast transferrin decreased and no incorporation of 14C lysine into transferrin could be detected by radioimmunoelectrophoresis. Thus this transferrin apparently was not synthesized by the placenta. When transferrin was removed from cryostat sections of placenta by treatment with chaotropic agents, subsequently added transferrin bound in an identical distribution. The specificity of this reaction was confirmed by the lack of binding of other serum proteins and by displacement procedures in which trophoblast transferrin was shown to be dislodged by transferrin added in vitro. These findings suggest that placental iron transport is predicated by binding of transferrin to specific receptors on trophoblast.