Effects of pregnant human, nonpregnant human, and fetal bovine sera on human chorionic gonadotropin, estradiol, and progesterone release by cultured human trophoblast cells

The impact of sex and sex hormones on cell function

The influence of sex on cellular function and metabolism is often ill defined in many human and animal studies. The National Institute of Health (NIH) recognized this gap in scientific knowledge and mandated that sex be factored into the design and data analysis of all cell culture and animal studies. Therefore, it is critical to understand how to incorporate sex in pre-clinical and clinical research. Here, we discuss how the sexual identify of cells influences experimental responses in cell culture and we highlight the importance of the culture media and its constituents to the function of cells. We further discuss the importance of understanding the influence and interactions between sex hormones and sex chromosomes. A deeper understanding of how sex chromosomes and sex hormones function as variables in complex biological systems may lead to better, more personalized medical therapies.

Hypercholesterolaemia in pregnancy as a predictor of adverse pregnancy outcome

BACKGROUND

Prevention of viable spontaneous preterm birth and low birth weight through screening is one of the key aims of antenatal care as these have implications for the child, mother and society. If women can be identified to be at high risk of these adverse birth outcomes in early pregnancy, they can be targeted for more intensive antenatal surveillance and prophylactic interventions.

OBJECTIVES

This study is therefore aimed to determine the association between elevated maternal serum cholesterol level in pregnancy and adverse pregnancy outcome.

METHODS

It was a prospective observational cohort study in which eligible participants were enrolled at gestational age of 14 to 20 weeks. Blood samples were obtained to measure total serum cholesterol concentrations and the sera were then analyzed enzymatically by the cholesterol oxidase: p-aminophenazone (CHOD PAP) method. Pregnancy outcomes were obtained by extraction from medical records and the labour ward register.

RESULTS

The incidences of the two adverse pregnancy outcomes examined in the study (preterm births and low birth weight (LBW) in term neonates) were 8.0% and 14.4% respectively. Preterm birth was 6.89-times more common in mothers with high cholesterol than in control mothers with normal total cholesterol level (38.5% versus 5.4%, P=0.029) while LBW was 7.99-times more common in mothers with high total maternal cholesterol than in mothers with normal cholesterol (87.5% versus 10.5%, P=0.019).

CONCLUSION

We can infer that the high maternal serum cholesterol (hypercholesterolaemia) is associated with preterm delivery/ low birth weight (LBW) in term infants. However, further validation of these findings with more robust prospective and longitudinal characterization of maternal serum cholesterol profiles is required in subsequent investigations.

Preterm delivery and low maternal serum cholesterol level: Any correlation?

BACKGROUND

The study assessed whether low maternal serum cholesterol during early pregnancy is associated with preterm delivery.

PATIENTS AND METHODS

It was a prospective observational cohort study involving pregnant women at gestational age of 14-20 weeks over a period of 12 months. Blood samples were obtained to measure total serum cholesterol concentrations and the sera were then analysed enzymatically by the cholesterol oxidase: p-aminophenazone (CHOD PAP) method.

RESULTS

The study showed an incidence of 5.0% for preterm delivery in the low risk study patients. Preterm birth was 4.83-times more common with low total maternal cholesterol than with midrange total cholesterol (11.8% versus 2.2%, P = 0.024).

CONCLUSION

Low maternal serum cholesterol (hypocholesterolaemia) is associated with preterm delivery. Optimal maternal serum cholesterol during pregnancy may have merit, therefore pregnant women should be encouraged to follow a healthy, balanced diet.

Establishment and characterization of a spontaneously immortalized trophoblast cell line (HPT-8) and its hepatitis B virus-expressing clone

BACKGROUND

Most trophoblast cell lines currently available to study vertical transmission of hepatitis B virus (HBV) are immortalized by viral transformation. Our goal was to establish and characterize a spontaneously immortalized human first-trimester trophoblast cell line and its HBV-expressing clone.

METHODS

Chorionic villi of Asian human first-trimester placentae were digested with trypsin and collagenase I to obtain the primary trophoblast cell culture. A spontaneously immortalized trophoblast cell line (HPT-8) was analyzed by scanning and transmission electron microscopy, cell cycle analysis, immunohistochemistry and immunofluorescence. HPT-8 cells were stably transfected with the adr subtype of HBV (HPT-8-HBV) and characterized by PCR and enzyme-linked immunosorbent assay.

RESULTS

We obtained a clonal derivative of a spontaneously immortalized primary cell clone (HPT-8). HPT-8 cells were epithelioid and polygonal, and formed multinucleate, giant cells. They exhibited microvilli, distinct desmosomes between adjacent cells, abundant endoplasm, lipid inclusions and glycogen granules, which are all characteristic of cytotrophoblasts. HPT-8 cells expressed cytokeratin 7, cytokeratin 18, vimentin, cluster of differentiation antigen 9, epidermal growth factor receptor, stromal cell-derived factor 1 and placental alkaline phosphatase. They secreted prolactin, estradiol, progesterone and hCG, and were positive for HLA-G, a marker of extravillous trophoblasts. HPT-8-HBV cells were positive for HBV relaxed-circular, covalently closed circular DNA and pre-S sequence. HPT-8-HBV cells also produced and secreted HBV surface antigen and HBV e antigen.

CONCLUSIONS

We established a trophoblast cell line, HPT-8 and its HBV-expressing clone which could be valuable in exploring the mechanism of HBV viral integration in human trophoblasts during intrauterine infection.

Metals in human placenta: focus on the effects of cadmium on steroid hormones and leptin

Cadmium and other metallic ions can act as metalloestrogens and endocrine disruptors of reproductive tissues and fetal development in mammals, including humans. The detrimental effects occur with respect to the synthesis of both steroid and polypeptide hormones in the placenta. Leptin is produced by the trophoblast and may regulate fetal organogenesis and development. In human term placentas, concentrations of toxic metals and their effects on steroidogenesis were assessed in healthy parturients (109 non-smokers and 99 smokers) in relation to tobacco smoking. Trace elements (cadmium, lead, iron, zinc and copper) were analyzed in placentas using atomic absorption spectroscopy, and steroid hormones (progesterone and estradiol) were assayed in placental samples by an enzyme-immunometric method. Cadmium concentrations were doubled in placentas of smokers as compared with non-smokers, and placental lead and zinc concentrations increased significantly. Placental concentrations of iron, copper, progesterone and estradiol did not differ. In addition, human trophoblast cells were co-cultured with 0, 5, 10 or 20 microm CdCl(2) for 96 h and leptin mRNA assessed by quantitative polymerase chain reaction. Leptin mRNA declined dose-responsively as a result of CdCl(2) exposure. Collectively, the results confirm that human placental tissue offers a unique opportunity to biomonitor cadmium exposure in both the maternal and the internal fetal environments. In addition, the results strongly suggest that cadmium may cause a decline in placental leptin synthesis, as we have previously shown for placental progesterone production. This may constitute further evidence of the endocrine-disrupting effects of cadmium, as a constituent of tobacco smoke, on reproduction in women.

The effect of estradiol on the expression of estrogen, progesterone, androgen, and prolactin receptors in human peritoneal fibroblasts

PURPOSE

To assess the ability of fibroblasts isolated from normal peritoneum and adhesion tissues to express various hormone receptors when cultured with exogenous estradiol.

METHODS

Primary cultures of fibroblasts from normal human peritoneum and adhesion tissue were treated with zero (control), 10(-10), 10(-8), and 10(-6) M concentrations of 17beta-estradiol. We performed real time reverse transcriptase polymerase chain reaction to determine mRNA levels of estradiol-alpha receptor (ER-alpha) and estradiol-beta receptor (ER-beta), progesterone receptor (P-R), androgen receptor (A-R), and prolactin receptor (PRL-R) in the two types of fibroblast cultures.

RESULTS

In the control groups, P-R and A-R were higher in normal than in adhesion fibroblasts. In adhesion cells, ER-alpha were higher at 10(-8) estradiol; ER-beta were higher at 10(-6) M estradiol; P-R remained constant; A-R showed a higher expression at 10(-10) and 10(-8) M estradiol; and PRL-R showed an exponential increase at 10(-10) M estradiol.

CONCLUSIONS

The inflammatory-like changes manifested by adhesion fibroblasts enhance the anabolic hormones receptor expression (ER-alpha, ER-beta, PRL, and A-R), when exposed to estradiol.

Adverse birth outcome among mothers with low serum cholesterol

OBJECTIVE

The objective of this study was to assess whether low maternal serum cholesterol during pregnancy is associated with preterm delivery, impaired fetal growth, or congenital anomalies in women without identified major risk factors for adverse pregnancy outcome.

METHODS

Mother-infant pairs were retrospectively ascertained from among a cohort of 9938 women who were referred to South Carolina prenatal clinics for routine second-trimester serum screening. Banked sera were assayed for total cholesterol; <10th percentile of assayed values (159 mg/dL at mean gestational age of 17.6 weeks) defined a "low total cholesterol" prenatal risk category. Eligible women were aged 21 to 34 years and nonsmoking and did not have diabetes; neonates were liveborn after singleton gestations. Total cholesterol values of eligible mothers were adjusted for gestational age at screening before risk group assignment. The study population included 118 women with low total cholesterol and 940 women with higher total cholesterol. Primary analyses used multivariate regression models to compare rates of preterm delivery, fetal growth parameters, and congenital anomalies between women with low total cholesterol and control subjects with mid-total cholesterol values >10th percentile but <90th percentile.

RESULTS

Prevalence of preterm delivery among mothers with low total cholesterol was 12.7%, compared with 5.0% among control subjects with mid-total cholesterol. The association of low maternal serum cholesterol with preterm birth was observed only among white mothers. Term infants of mothers with low total cholesterol weighed on average 150 g less than those who were born to control mothers. A trend of increased microcephaly risk among neonates of mothers with low total cholesterol was found. Low maternal serum cholesterol was unassociated with risk for congenital anomalies.

CONCLUSIONS

Total serum cholesterol <10th population percentile was strongly associated with preterm delivery among otherwise low-risk white mothers in this pilot study population. Term infants of mothers with low total cholesterol weighed less than control infants among both racial groups.

Heparin and aspirin attenuate placental apoptosis in vitro: implications for early pregnancy failure

OBJECTIVE

Live birth rates are increased by treatment with heparin and aspirin in cases of poor pregnancy outcome such as antiphospholipid syndrome. Both drugs may attenuate miscarriage by inhibiting aberrant coagulation or by modulating trophoblast apoptosis. Here we assessed their roles in trophoblast apoptosis in vitro.

STUDY DESIGN

BeWo cells and placental villi were cultured in sera from women with successful or failing in vitro fertilization, with and without heparin or aspirin. Apoptosis was assessed by using DNA laddering, cytokeratin 18 neoepitope formation, Bcl-2, and caspase 7 expression.

RESULTS

In BeWo cells, sera from in vitro fertilization failure increased trophoblast apoptosis, whereas heparin and aspirin reversed these effects. In villous trophoblast, heparin increased Bcl-2 and cytokeratin 18 protein expression. Heparin and aspirin inhibited DNA laddering.

CONCLUSION

Heparin and aspirin modulate trophoblast apoptosis suggesting a direct impact on trophoblast biology, thus providing an additional mechanism to explain the clinical benefits of heparin and aspirin on recurrent pregnancy loss.

Endocrine disruption by cadmium, a common environmental toxicant with paradoxical effects on reproduction

Cadmium (Cd(2+)) is a common environmental pollutant and a major constituent of tobacco smoke. Exposure to this heavy metal, which has no known beneficial physiological role, has been linked to a wide range of detrimental effects on mammalian reproduction. Intriguingly, depending on the identity of the steroidogenic tissue involved and the dosage used, it has been reported to either enhance or inhibit the biosynthesis of progesterone, a hormone that is inexorably linked to both normal ovarian cyclicity and the maintenance of pregnancy. Thus, Cd(2+) has been shown to exert significant effects on ovarian and reproductive tract morphology, with extremely low dosages reported to stimulate ovarian luteal progesterone biosynthesis and high dosages inhibiting it. In addition, Cd(2+) exposure during human pregnancy has been linked to decreased birth weights and premature birth, with the enhanced levels of placental Cd(2+) resulting from maternal exposure to industrial wastes or tobacco smoke being associated with decreased progesterone biosynthesis by the placental trophoblast. The stimulatory effects of Cd(2+) on ovarian progesterone synthesis, as revealed by the results of studies using stable porcine granulosa cells, appear centered on the enhanced conversion of cholesterol to pregnenolone by the cytochrome P450 side chain cleavage (P450scc). However, in the placenta, the Cd(2+)-induced decline in progesterone synthesis is commensurate with a decrease in P450scc. Additionally, placental low-density lipoprotein receptor (LDL-R) mRNA declines in response to Cd(2+) exposure, suggesting an inhibition in the pathway that provides cholesterol precursor from the maternal peripheral circulation. Potential mechanisms by which Cd(2+) may affect steroidogenesis include interference with the DNA binding zinc (Zn(2+))-finger motif through the substitution of Cd(2+) for Zn(2+) or by taking on the role of an endocrine disrupting chemical (EDC) that could mimic or inhibit the actions of endogenous estrogens. Divergent, tissue-specific (ovary vs. placenta) effects of Cd(2+) also cannot be ruled out. Therefore, in consideration of the data currently available and in light of the potentially serious consequences of environmental Cd(2+) exposure to human reproduction, we propose that priority should be given to studies dedicated to further elucidating the mechanisms involved.

Placental endocrine disruption induced by cadmium: effects on P450 cholesterol side-chain cleavage and 3beta-hydroxysteroid dehydrogenase enzymes in cultured human trophoblasts

We previously suggested that cadmium (Cd), an environmental toxicant and constituent of tobacco smoke, inhibits progesterone secretion in cultured human placental trophoblasts by inhibiting low-density lipoprotein receptor mRNA expression. In the current study, we investigated whether Cd also disrupts progesterone synthesis via P450 cholesterol side-chain cleavage (P450(scc)) and 3beta-hydroxysteroid dehydrogenase (3beta-HSD), enzymes that play important roles in placental steroidogenesis. Human cytotrophoblasts were purified by density gradient centrifugation and incubated in Dulbecco modified Eagle medium + 10% fetal bovine serum with 0, 5, 10, or 20 microM CdCl(2) for 96 h. Cells progressed to syncytiotrophoblastic maturity regardless of treatment. No differences (P > 0.05) in cell protein and lactate dehydrogenase activity were observed between untreated trophoblasts and those treated with CdCl(2). However, P450(scc) and 3beta-HSD mRNA transcript levels declined in a dose-dependent manner (P <0.05) in trophoblasts cocultured with 5, 10, or 20 microM CdCl(2). P450(scc) activity was similarly inhibited (P < 0.05) by CdCl(2) treatment, although 3beta-HSD activity was not significantly affected. Coculture with 8-bromo-cAMP enhanced progesterone secretion in untreated cultures but did not reverse the decline in progesterone secretion induced by CdCl(2) treatment. CdCl(2) failed to influence cAMP content in cultured cells. Collectively, results suggest that P450(scc) enzyme is another site at which Cd interferes with placental progesterone production. However, it is unlikely that an inhibition of cAMP is involved with the inhibition of progesterone biosynthesis by Cd in human trophoblasts.

Leptin in pregnancy

Leptin is a polypeptide hormone that aids in the regulation of body weight and energy homeostasis and is linked to a variety of reproductive processes in both animals and humans. Thus, leptin may help regulate ovarian development and steroidogenesis and serve as either a primary signal initiating puberty or as a permissive regulator of sexual maturation. Perhaps significantly, peripheral leptin concentrations, adjusted for adiposity, are dramatically higher in females than in males throughout life. During primate pregnancy, maternal levels that arise from adipose stores and perhaps the placenta increase with advancing gestational age. Proposed physiological roles for leptin in pregnancy include the regulation of conceptus growth and development, fetal/placental angiogenesis, embryonic hematopoiesis, and hormone biosynthesis within the maternal-fetoplacental unit. The specific localization of both leptin and its receptor in the syncytiotrophoblast implies autocrine and/or paracrine relationships in this endocrinologically active tissue. Interactions of leptin with mechanisms regulating pre-eclampsia and maternal diabetes have also been suggested. Collectively, therefore, reports suggest that a better understanding of the regulation of leptin and its role(s) throughout gestation may eventually impact those causes of human perinatal morbidity and mortality that are exacerbated by intrauterine growth retardation, macrosomia, placental insufficiency, or prematurity.

Leptin receptor transcripts are constitutively expressed in placenta and adipose tissue with advancing baboon pregnancy

The baboon (Papio sp.) is an accepted nonhuman primate model for the study of the endocrinology of human pregnancy. To further characterize this model with regard to leptin function, messenger RNA transcripts for both long (Ob-RL) and short (Ob-RS) leptin receptor isoforms were identified in maternal tissues at various stages of gestation. Thus, placental villous, subcutaneous and omental adipose tissues were collected upon cesarean delivery at early (Days 60-62), mid (Days 98-102) and late (Days 159-164) pregnancy (term approximately 184 days). Additionally, amniochorion, decidua, and corpus luteum were collected in late gestation. Expression of Ob-RL and Ob-RS transcripts was determined in relation to constitutively expressed glyceraldehyde-3-phosphate dehydrogenase via reverse transcriptase-polymerase chain reaction, and transcripts were localized within specific placental cell types by in situ hybridization. Ob-RL and Ob-RS transcripts were present in amniochorion, decidua, and corpus luteum at term and appeared constitutively expressed throughout gestation in placenta and adipose tissues. Ob-RS was expressed in greater (P < 0.02) abundance than Ob-RL in all tissues. Within the placenta, receptor isoforms were localized predominantly to the syncytiotrophoblast. The expression of leptin receptor transcripts in maternal adipose tissues, as well as in the syncytiotrophoblast, amniochorion, decidua, and corpus luteum, suggests the potential for autocrine/paracrine roles for the polypeptide in the endocrinology of primate pregnancy. These are the first such observations in a nonhuman primate and support the use of the baboon as a model for the study of leptin in human pregnancy.

Human villous macrophage-conditioned media enhance human trophoblast growth and differentiation in vitro

In human chorionic villi, numerous macrophages, so-called Hofbauer cells, are located adjacent to trophoblasts. To determine the role of the macrophages in the proliferation and differentiation of trophoblasts, cytotrophoblast cells were cultured in serum-free culture-conditioned media of villous macrophages (VMCM), peritoneal macrophages (PMCM), and villous fibroblasts (VFCM). In VMCM, proliferation of cytotrophoblast cells was detected at 24 h by immunocytochemistry with Ki-67-antibody. A large number (P < 0.001) of multinucleated syncytia was formed in VMCM. In VMCM, cytotrophoblast cell fusion was completed by 96 h, which coincided with the peak of hCG secretion and initiation of human placental lactogen (hPL) release. Levels of hCG (P < 0.001) and hPL (P < 0. 001) secretion from syncytial cells were significantly higher in VMCM than in PMCM or in VFCM. Concentrations of macrophage colony-stimulating factor (M-CSF) and vascular endothelial growth factor (VEGF) analyzed by ELISA were greater in VMCM than in PMCM or in VFCM, whereas monocyte chemoattractant protein-1 (MCP-1) concentration was high in PMCM. The expression patterns of M-CSF, VEGF, and MCP-1 in villous macrophages and peritoneal macrophages by reverse transcriptase-polymerase chain reaction were similar to their secretion patterns. Thus, villous macrophages have a greater ability to stimulate hCG and hPL secretion than do peritoneal macrophages. This study suggests that macrophages within the villous stroma may stimulate the growth and differentiation of trophoblasts through their secreted substances.

Oestradiol stimulates morphological and functional differentiation of human villous cytotrophoblast

Trophoblast differentiation is a complex process involving interactions of cytotrophoblastic cells with their evolutive milieu. During pregnancy, the feto-placental unit produces large amounts of steroids. Progesterone and oestradiol are increasingly produced when the syncytiotrophoblast is highly differentiated. Furthermore, receptors to these hormones are expressed by the trophoblast. This led us to test the hypothesis that steroid production could affect the morphological and functional differentiation of the trophoblast during gestation. The fusion of cytotrophoblastic cells into syncytiotrophoblast was assessed using fluorescence recovery after photobleaching for gap junctional communication analysis (gap-FRAP), desmoplakin immunostaining and connexin 43 expression. In parallel, functional differentiation was assessed by beta-human chorionic gonadotrophin (betahCG) production and human chorionic somatomammotropin (hCS) expression analysis. The presence of oestradiol, 1 microm, increased the percentage of coupled cells (3. 8-fold), connexin 43 expression and stimulated the syncytium formation. In parallel, oestradiol (1, 3 and 5 microm) induced a significant increase in the daily hCG production. The steroid action was specific, as the stimulatory effects were inhibited by tamoxifen. Oestradiol also stimulated hCS expression (51 per cent compared to control after 3 days). As trophoblastic differentiation is specifically stimulated by hCG, oestradiol could act via the stimulation of hCG production or via a direct action. In the presence of an efficient concentration of hCG antibody, oestradiol still stimulated hCS expression, suggesting a self-sufficient effect of the steroid. Physiological concentrations of progesterone were ineffective in modulating trophoblast differentiation. In conclusion, oestradiol could be implicated in the maturation and aging of the trophoblast.

Serum leptin concentrations and expression of leptin transcripts in placental trophoblast with advancing baboon pregnancy

Leptin is a polypeptide hormone originally thought to be produced exclusively by adipocytes. Recently, however, both leptin messenger ribonucleic acid (mRNA) and leptin protein were identified in human placental trophoblast cells, suggesting a potential role in primate pregnancy. In the present study, venous blood samples were collected at 5-day intervals during gestation from baboons (Papio sp), an established model for the study of human pregnancy, as well as from nonpregnant baboons, and leptin concentrations were determined by RIA. Additionally, placental villous tissue was collected upon cesarean delivery at early (days 60-62; n = 5), mid (days 98-102; n = 5), and late (days 159-167; n = 5) gestation (term = approximately 184 days), and leptin mRNA was quantitated by competitive RT-PCR. Finally, in situ hybridization was employed to localize transcripts to specific placental cell types. Results determined that maternal leptin levels (mean +/- SEM), which were dramatically greater (P<0.01) than those in nonpregnant cycling baboons (1.4+/-0.1 ng/mL), increased (P<0.005) with gestational age from 63.6+/-10.4 ng/mL on day 60 of gestation to 157.8+/-16.1 near term. Levels declined to those found in cycling baboons by 15 days postdelivery. In contrast to maternal leptin concentrations, placental leptin mRNA decreased (P<0.02) with advancing pregnancy, as transcript abundance declined approximately 8-fold from early to late gestation. Maternal peripheral leptin concentrations were positively correlated (r = 0.66; P<0.001) whereas placental leptin mRNA levels were negatively correlated (r = -0.64; P<0.01) with gestational age. Expression of leptin mRNA transcripts, as evidenced by RT-PCR in villous tissue, was localized principally within syncytiotrophoblast by in situ hybridization. In summary, changes in maternal peripheral leptin concentrations and placental leptin mRNA abundance that occur commensurate with advancing gestational age may imply evolving roles for the polypeptide with advancing primate pregnancy. In this capacity, localization of leptin transcripts within the baboon syncytiotrophoblast suggests the potential for autocrine or paracrine interactions within this endocrinologically active tissue. Finally, both the similarities in leptin ontogeny in baboon and human pregnancy and the singular enhancement of maternal leptin levels inherent throughout baboon gestation emphasize the potential of this nonhuman primate model for the study of leptin action in the maternal-fetoplacental unit.

Cadmium accumulation and effects on progesterone release by cultured human trophoblast cells

This study was designed to examine the characteristics of cadmium bioaccumulation by human trophoblast cells in culture and the subsequent effect of cadmium exposure on progesterone production and syncytial formation. The accumulation of cadmium suggested a time- and dose-dependent relationship, although it was not significant. The rate of metal accumulation was similar in all cadmium-treated groups. After 72 h of continuous exposure to cadmium concentrations of 5, 10, and 20 microM, progesterone release was diminished to 69, 51, and 38% of control values (P < 0.05), respectively. When cells were exposed to cadmium from 72 to 96 h (after syncytial development), progesterone release exhibited the same pattern of decline in response to increasing cadmium concentrations. Histologic evaluation of whole mounts of trophoblast cells exposed to 20 microM CdCl2 for 96 h revealed that syncytial formation seemed to be uninhibited. The pattern of cadmium-accumulation by normal cultured human trophoblast cells suggests a time- and dose-relationship with a concomitant decrease in progesterone release that occurs without apparent inhibition of syncytial development.

Effects of reduced maternal lipoprotein-cholesterol availability on placental progesterone biosynthesis in the baboon

Maternal low density lipoprotein (LDL) is the principal source of cholesterol substrate for progesterone biosynthesis in the primate placental syncytiotrophoblast. The relationship of LDL-cholesterol availability and other potential cholesterol-yielding pathways to placental progesterone production have not, however, been demonstrated in vivo in a nonhuman primate. Therefore, maternal peripheral lipoprotein-cholesterol and progesterone concentrations were determined in blood samples obtained by venipuncture, from day 72 until day 100, from pregnant baboons (Papio sp) that were either untreated (n = 4) or treated (n = 3) with the inhibitor of hepatic lipoprotein production, 4-aminopyrazolo [3-4-d]pyrimidine (4-APP, 10 mg/kg BW) on days 98-99 of pregnancy (term = 184 days). Although LDL-cholesterol and progesterone levels remained unchanged in untreated animals, LDL-cholesterol concentrations were 9-fold lower (P < 0.005) in baboons receiving 4-APP than in untreated baboons 2 days following initial administration. Commensurate progesterone levels were 3.5-fold lower (P < 0.03) in 4-APP-treated baboons than in untreated baboons. RT-PCR was used to approximate relative changes in transcription of messengers RNAs (mRNAs) for selected cholesterol-sensitive pathways in placental tissue collected on day 100. Thus, expression of mRNAs for LDL receptor and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase appeared enhanced, whereas acyl-coenzyme A:cholesterol acyl transferase (ACAT) mRNA was diminished in syncytiotrophoblast-enriched cell fractions as a result of 4-APP administration. No relative differences in mRNAs were apparent in whole placental villous tissue, however, as a result of 4-APP treatment. In summary, this experiment demonstrates a significant decline in progesterone production elicited by maternal LDL-cholesterol withdrawal, and attests to the efficacy of 4-APP administration during baboon pregnancy. These results also suggest a commensurate regulation of cholesterol-sensitive pathways in primate syncytiotrophoblast. However, no relative differences were apparent in mRNA levels for LDL receptor, HMG-CoA and ACAT in whole placental villous tissue as a result of LDL-cholesterol withdrawal, which may suggest potential disparities in the mechanisms regulating cholesterol homeostasis in steroidogenically active syncytiotrophoblasts vs. those in proliferative nonendocrine placental constituents.