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PubMed1987

Attachment of blastocysts to lens capsule: a model system for trophoblast-epithelial cell interaction on a natural basement membrane.

The bovine lens capsule has previously been shown to provide an optimal surface for the examination of epithelial cell interaction with a basement membrane. This native substrate has been used to investigate some initial aspects of attachment of mouse blastocysts and trophoblastic cellular outgrowth. Mouse blastocysts were presented to the cell-free humoral side of the anterior lens capsule, incubated for 72 h, and examined by scanning and transmission electron microscopy. Blastocysts hatch and attach from their zonae pellucidae by 30 h. Trophoblastic cells proliferate rapidly in a coronal direction, display extensive surface microvilli, and advance by the extension of numerous filipodia, many of which terminate with bulbous projections. These projections were shown by transmission electron microscopy to contain numerous vacuoles and polysomes. To simulate further the initial blastocyst-uterine interaction, a suspension of lens epithelial cells was introduced to the capsule and permitted to form a monolayer prior to the addition of the blastocysts. At 72 h the monolayer of lens cells remained intact. We observed that: a) lens cells appear to recede from the advancing trophoblastic cells, and b) trophoblastic cells extend beneath the monolayer of lens cells and thereby dislodge the cells from the lens capsule substrate. No infiltration of the capsule by the advancing trophoblastic cells was observed. The lens capsule appears to offer a promising system for the study of trophoblast-epithelial cell interaction on a natural basement membrane.

Animals↗
PubMed1988

The dynamic structure of rabbit blastocyst coverings. II. Ultrastructural evidence for a role of the trophoblast in neozona formation.

The neozona is the innermost layer of the complex blastocyst coverings of the rabbit and is located between the mucoprotein layer and the trophoblast. As shown previously the neozona begins to replace the zona pellucida from the 4th day post coitum (d p.c.) on (Denker and Gerdes 1979). In the present study, rabbit blastocyst coverings were checked for regional differences in their composition, comparing the embryonic and the abembryonic pole of the blastocyst, at 5 and 6 d p.c. These two stages were chosen because at 5 d p.c. a complete trophoblast layer is still present at both the embryonic disc (Rauber's layer) and the extraembryonic regions (mural and abembryonic pole trophoblast), whereas at 6 d p.c. Rauber's layer has largely degenerated. Correlation of regional differences in blastocyst coverings structure with presence or absence of an intact trophoblast is taken as suggestive evidence for a role of the trophoblast in the formation or the structural modification of blastocyst coverings components. Blastocysts of both stages were fixed in glutaraldehyde with and without ruthenium red and processed for TEM. The neozona was found to be almost equally well developed in all regions at 5 d p.c. On contrast, at 6 d p.c. (Rauber's layer defective) the neozona is consistently found to be much thinner at the embryonic disc than in the extraembryonic regions where the trophoblast is still intact. This is the first report on regional differences of the structural composition of blastocyst covering within the same blastocyst.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Developmental changes in the cell columns and trophoblastic shell of the macaque placenta: an immunohistochemical study localizing type IV collagen, laminin, fibronectin and cytokeratins.

Developmental changes in the organization of cells and extracellular matrix in the cell columns and trophoblastic shell of macaque placentas have been examined between 37 days of gestation and term. Between 37 and 53 days a thickened basement membrane developed between the trophoblast cells of the proximal cell columns and the mesenchymal cores of contiguous anchoring villi. This layer stained strongly for type IV collagen and laminin, but weakly for fibronectin. Large "lakes" of extracellular matrix immunoreactive for all 3 of these antigens were present in the distal columns, while smaller amounts were distributed between cells of the proximal columns. During this period the trophoblast cells in the proximal shell reorganized, forming strands of cells that were separated by bands of matrix immunoreactive for type IV collagen, laminin, and fibronectin. Staining for these antigens decreased abruptly at the junction between fetal and maternal tissues. Between 66 and 104 days the thick basement membrane of the proximal columns persisted, but stained only weakly for each of the 3 extracellular matrix antigens. The large lakes of matrix in the distal columns characteristic of earlier stages gradually disappeared. The cell columns became progressively shorter and the tips of the anchoring villi became embedded in the trophoblastic shell. The matrix of the shell decreased in immunostaining intensity except for narrow rims around the trophoblast cells. Gestational ages later than 104 days showed few additional changes in the distribution of the matrix antigens or cell organization of the columns and shell. The thick basement membrane-like layer persisted to term although it continued to stain weakly for the 3 matrix antigens. The distal ends of most anchoring villi were embedded in the trophoblastic shell. The developmental changes in the organization of the columns and shell may be related to changes in placental growth rate.

Animals↗
PubMed1993

Localization and production of immunoreactive endothelin-1 in the trophoblast of human placenta.

Regarding their endocrine and paracrine activities, endothelins can be considered as peptide hormones and growth factors. The presence of endothelin-1 (ET-1)-binding sites on smooth muscle of placental villous vessels, on villous trophoblast and on purified trophoblast in culture raises the question of the origin of the peptide. In placenta, endothelin could derive from maternal, fetal and/or endogenous sources. Therefore, localization of ET-1 was investigated by use of immunohistochemistry in human term placenta and in cultured trophoblast using the avidin-biotin-peroxidase complex procedure. Specificity of immunostaining was demonstrated by applying ET-1 antibody that has been preabsorbed with excess peptide. In sections of placenta, ET-1 immunoreactivity (ET-1 IR) was specifically detected in the endothelium of the vessels and in the syncytiotrophoblast of the villi. ET-1 IR was also detected in the decidua-like cells and in the extravillous cytotrophoblast of the basal plate, a region where the maternal and fetal cells intermingle closely. The extravillous cytotrophoblast of the chorionic plate and of the placental septa also exhibited a strong ET-1 IR. For trophoblast culture cytotrophoblastic cells were obtained from placental villi by trypsin-DNase dispersion, further purified on Percoll gradient and enriched by employing a monoclonal anti-HLA class-I antibody. The trophoblastic origin of the cells was demonstrated by immunohistochemistry and by studying the secretion of gestational hormones during culture. After different periods of culture of purified cytotrophoblastic cells (1 to 5 days), ET-1 IR was observed in 95% of cells: cytotrophoblastic cells, trophoblast aggregates, and syncytiotrophoblast.(ABSTRACT TRUNCATED AT 250 WORDS)

Cells, Cultured↗
PubMedDate not supplied

Reduced systemic toxicity from superselective chemoembolization compared with systemic chemotherapy in patients with high-risk metastatic gestational trophoblastic disease.

PURPOSE: The efficacy of chemoembolization of primary and metastatic gestational trophoblastic neoplasms was studied. METHODS: Six female patients, 19-33 years old, with high-risk trophoblastic disease were subjected to one to five chemoembolizations in 3-week intervals. Three of the patients had metastases to the liver, 2 had local tumor extension to the pelvic wall, and all 5 had failed initial systemic chemotherapy. The sixth patient was treated for a trophoblastic remnant following surgical expression of a tubal pregnancy. For follow-up, beta hCG levels in urine and serum and dynamic or angio-computed tomograms were obtained in biweekly to 6-month intervals. RESULTS: Two of 3 patients with liver metastases are alive and free of disease 6 and 7 years after initial chemoembolization. The third is alive at 3 years but with evidence of recurrent disease. Two patients treated for locally invasive trophoblastic disease died 3 months and 4 years, respectively, after initial chemoembolization. One had a 2 1/2 -year remission. The patient treated for a trophoblastic remnant in the tube is alive and free of disease at 6-year follow-up. Hematologic toxicity occurred in only one. CONCLUSION: Selective chemoembolization in our small series of patients with high-risk trophoblastic disease was equally effective as results reported for multi-drug systemic chemotherapy but had markedly lower renal, liver, and hematologic toxicity.

Adult↗
PubMed2003

Developmental changes in the ploidy of mouse implanting trophoblast cells in vitro.

Shortly after the onset of implantation, polar mouse trophoblast cells proliferate and give rise to the ectoplacental cone, constituted by two distinct cell populations: undifferentiated, diploid cells and giant cells. Giant cells characteristically exhibit exaggerated dimensions and polyploid nuclei. In this study, we employ ectoplacental cones as a dynamic source of trophoblast giant cells to analyze cell proliferation, cell death, and ploidy under in vitro conditions. Our results show that DNA synthesis and the increase in the cell number are relevant only during the first 24 h of culture. Subsequently, DNA synthesis still occurs, mainly in the giant cell compartment, while the number of cells gradually decreases. Cell death by injury and apoptosis was also observed in the non-giant cell compartment of the ectoplacental cone. These findings suggest that the first 24 h of culture are crucial to the mitotic activity of the ectoplacental cone cells that gradually ceases, favoring the endoreduplication process. The DNA synthesis index during the subsequent experimental intervals emphasizes accumulation of DNA for the polyploidization. There was clear correlation between DNA content and nuclear dimension. The ploidy values for the trophoblast giant cells varied from 2C up to 368C in the giant cells, but were not as expressive as those known from in vivo conditions, probably due to the absence of regulatory factors specific to the embryonic-maternal interface. In situ hybridization and histochemistry for the nucleolus-organizing region showed that trophoblast nuclei have only two marker signals, indicative of a typical polytenic process. This present study elucidates important aspects of trophoblast behavior and provides new information on trophoblast physiology in vivo and in vitro.

Animals↗
PubMed1999

Calomys callosus (Rodentia : Cricetidae) trophoblast cells as host cells to Toxoplasma gondii in early pregnancy.

The potential of the RH strain of Toxoplasma gondii to invade trophoblast cells of the cricetid rodent Calomys callosus in a congenital infection in the initial third of pregnancy was investigated in this study using morphological and immunocytochemical approaches. The animals were intraperitoneally inoculated on the 1st day of pregnancy and the infection was observed on day 7. Various numbers of parasites could be observed inside the parasitophorous vacuoles in trophoblastic cells under light and electron microscopy. The trophoblast cells showed characteristics of healthy cells, and no alteration other than parasite vacuoles in their cytoplasm could be detected. Polyclonal or monoclonal anti-T. gondii antibodies (respectively, anti-T. gondii components and the major surface parasite antigen p30) labeled both the parasite surface and parasitophorous vacuole membranes, regardless of the number of parasites inside the compartment. In addition, p30-containing trails were detected in the extracellular matrix surrounding trophoblastic cells similar to those found with other parasites during locomotion and the invasion process. Our results show the ability of T. gondii to infect trophoblast cells during the early blastocyst-endometrial relationship and open new possibilities for more accurate study of the invasion process of this parasite and the role of the trophoblast as an embryo defense barrier.

Animals↗
PubMed2003

Elevated concentration of TNF-alpha induces trophoblast differentiation in mouse blastocyst outgrowths.

Elevated expression of tumour necrosis factor-alpha (TNF-alpha) is associated with adverse pregnancy outcome. This study has examined the expression of TNF-alpha and its receptors (TNF-Rs) by mouse blastocysts and blastocyst outgrowths from day 4 to 9.5 of pregnancy and investigated the effects of elevated TNF-alpha on the inner cell mass (ICM) and trophoblast cells of blastocyst outgrowths. RT-PCR demonstrated TNF-alpha mRNA expression from day 7.5 to 9.5, TNF-R1 from day 6.5 to 9.5 and TNF-R2 from day 5.5 to 7.5 of pregnancy, and in situ hybridisation revealed the trophoblast giant cells (TGCs) of the early placenta as the site of TNF-alpha expression. Day 4 blastocysts were cultured in a physiologically high concentration of TNF-alpha (100 ng/ml) for 72 h to the outgrowth stage and then compared to blastocysts cultured in media alone. TNF-alpha-treated blastocyst outgrowths exhibited a significant reduction in ICM cells (mean +/- SD 23.90+/-10.42 vs 9.37+/-7.45, t-test, P<0.0001) with no significant change in the numbers of trophoblast cells (19.97+/-8.14 vs 21.73+/-7.79, t-test, P=0.39). Within the trophoblast cell population, the TNF-alpha-treated outgrowths exhibited a significant increase in multinucleated cells (14.10+/-5.53 vs 6.37+/-5.80, t-test, P<0.0001) and a corresponding significant decrease in mononucleated cells (5.87+/-3.60 vs 15.37+/-5.87, t-test, P<0.0001). In summary, this study describes the expression of TNF-alpha and its receptors during the peri-implantation period in the mouse. It also reports that elevated TNF-alpha restricts ICM proliferation in the blastocyst and changes the ratio of mononucleated to multinucleated trophoblast cells. These findings suggest a mechanism by which increased expression of TNF-alpha during trophoblast differentiation may be detrimental to pregnancy.

Animals↗
PubMed1988

Dietary factors and risk of trophoblastic disease.

The risk of gestational trophoblastic disease in relation to frequency of consumption of selected dietary items was evaluated with data from a case-control study conducted in Northern Italy on 148 women with histologically confirmed gestational trophoblastic disease and two control groups, one consisting of 372 obstetric control subjects and one consisting of 406 patients in the hospital for acute, nonobstetric, nongynecologic conditions. Patients with gestational trophoblastic disease tended to consume several foods less frequently, including the major sources of vitamin A and animal protein in the Italian diet. Relative risk estimates were significantly below unity in both control groups for green vegetable, carrot, liver, and cheese consumption and in the obstetric control group only for milk, meat, eggs, fresh fruit, and fish. Inverse relationships emerged between the risk of gestational trophoblastic disease and beta-carotene or retinol intake index. The trend of decreasing risk with increasing intake was significant for beta-carotene consumption. The present findings confirm that various aspects of diet may influence the risk of gestational trophoblastic disease. However, the limitation of available evidence still introduces serious uncertainties in the interpretation of these findings and suggests the potential importance of further epidemiologic and biochemical research to obtain more precise definition of specific dietary correlates of gestational trophoblastic disease.

Adolescent↗
PubMed1989

Trophic effects of first-trimester human trophoblasts and human chorionic gonadotropin on lymphocyte proliferation.

We examined the effects of pure first-trimester human trophoblast cells grown in long-term cultures or their secreted products on the proliferation of human peripheral blood lymphocytes cultured alone, under allogeneic stimulation, or in the presence of concanavalin A. Both trophoblasts and their culture supernatants stimulated lymphocyte proliferation. Culture supernatant had a moderate enhancing effect on lymphocyte mitogenesis in mixed lymphocyte cultures and in the presence of concanavalin A. Anti-human chorionic gonadotropin antibody suppressed the proliferative effect of trophoblast cells and their supernatants in the above experiments in a dose-dependent manner. At physiologic concentrations, both pure and impure forms of human chorionic gonadotropin enhanced (in a dose-dependent manner) proliferation of lymphocytes cultured alone (peak stimulation index, 6 to 7.8 at approximately 7 IU/ml). At higher concentrations (20 to 400 IU/ml) the proliferative effect was abolished. Trophoblast culture supernatant induced the expression of interleukin-2 receptors on lymphocytes after 48 hours of incubation. The supernatant also stimulated proliferation of human colon carcinoma cells. Thus trophoblast or trophoblast-derived human chorionic gonadotropin has a lymphocytotrophic function that may have implications for fetal survival.

Carcinoma↗
PubMed1991

Cytotoxic activity against trophoblast and choriocarcinoma cells of large granular lymphocytes from human early pregnancy decidua.

Large granular lymphocytes (LGL) are the most abundant cell type in first trimester human pregnancy decidua. We have shown previously that CD56-positive decidual LGL have cytotoxic activity against the natural killer (NK) target K562, and that this cytotoxicity is augmented by pretreatment with interleukin-2 (IL-2). We now report that flow cytometrically purified populations of CD56-positive decidual LGL have no cytotoxic activity against either the BeWo choriocarcinoma cell line or freshly isolated term trophoblast. Incubation of unfractionated decidual cells with IL-2 induced cytotoxicity against BeWo, but term trophoblast remained resistant to lysis. Both BeWo and trophoblast showed much lower binding frequencies to decidual or peripheral blood cells than K56 targets, and excess trophoblast did not inhibit cytotoxic activity against K562. This suggests that the resistance of trophoblast to lysis by either decidual or peripheral blood LGL is due to the lack of accessible NK target structures on the surface of trophoblast.

Choriocarcinoma↗
PubMed1992

HPL-positive infiltrating trophoblastic cells in normal and abnormal pregnancy.

In a series of 24 pregnant women, placental bed biopsies were performed in the third trimester at cesarean section. All the resulting specimens contained infiltrating trophoblast with both small and giant cells, and eight also contained vascular trophoblast. On immunoperoxidase staining for HPL, some small interstitial trophoblastic cells were positive in 12 cases. Some cells of the vascular intramural trophoblast and practically all cells of the vascular intraluminal trophoblast were positive. Seven cases were normal pregnancies whereas 17 were complicated by arterial hypertension and/or fetal growth retardation. A significant correlation between abnormal pregnancy and absence of HPL-positive interstitial cells in the placental bed biopsy was found. This probably indicates a diminished overall number of HPL-positive interstitial cells in the group of abnormal pregnancies and might reflect some defect of interstitial trophoblast. Such a defect may play a role in the arrest of the physiological changes of pregnancy in spiral arteries, which has been described in pre-eclampsia and in many cases of idiopathic fetal growth retardation.

Biopsy↗
PubMed1995

First-trimester endocervical irrigation: feasibility of obtaining trophoblast cells for prenatal diagnosis.

We sought to determine the feasibility of obtaining trophoblast cells for first-trimester prenatal diagnosis using endocervical irrigation. We studied 20 pregnant patients between 7-10.5 weeks' gestation who presented for elective pregnancy termination. Under ultrasound guidance, a specially designed plastic catheter was advanced to the level of the internal cervical os. Gentle flushing and aspiration was performed with 3 mL of normal saline. The material obtained was fixed and stained. A placental pathologist identified trophoblast cells using light microscopy. In another five cases, we attempted to culture the endocervical washings. Trophoblast cells were identified by microscopy after staining the cultured material with an anti-alpha-hCG-antibody bound stain. In ten of 20 cases (50%), trophoblast material was retrieved on irrigation. Of the five additional cases on which culture was attempted, trophoblast was successfully cultured in one, the results were equivocal in two, and culture was unsuccessful in the other two. Trophoblast cells for prenatal diagnosis can be obtained in a significant percentage of cases by first-trimester endocervical irrigation. The advantages of irrigation include technical simplicity, brief duration (less than 3 minutes), and suitability to first-trimester diagnosis. Further testing is necessary to determine the risks.

Cells, Cultured↗
PubMed1996

Nitric oxide synthase activities in human myometrium and villous trophoblast throughout pregnancy.

OBJECTIVE: To study the changes in nitric oxide synthase activities in human myometrium and trophoblast throughout pregnancy and around delivery. METHODS: Samples of villous trophoblast were collected from women undergoing elective cesarean delivery at term (n = 12) or voluntary termination of pregnancy in the first (n = 27) or second (n = 11) trimesters of pregnancy. Myometrial samples were obtained from nonpregnant women undergoing hysterectomy (n = 5) and pregnant women both before (n = 7) and after (n = 7) the onset of spontaneous labor at term. Nitric oxide synthase activity was quantified for homogenized samples using the L-citrulline assay in the presence and absence of calcium. RESULTS: The highest levels of nitric oxide synthase activity were found in first-trimester villi (range 2-29 nmol L-citrulline/minute/g protein), with a significant fall in activity in the third trimester (range 2-10 nmol L-citrulline/minute/g protein; P < .001 for both calcium-dependent and calcium-independent activity). Myometrial activities were relatively low compared with those in the trophoblast (0-2 nmol L-citrulline/minute/g protein), with no significant differences in calcium-dependent activities between subgroups. Myometrial calcium-independent activities were lower in pregnant than in nonpregnant women (P = .007), with those in labor having levels higher than those not in labor (P = .048). CONCLUSION: Levels of nitric oxide synthase activity are relatively high in villous trophoblast, particularly during the first trimester. Although the contribution to total nitric oxide production in the uterus by myometrial nitric oxide synthase appears to be relatively small, nitric oxide produced by the trophoblast may play a role in maintaining uterine quiescence by a paracrine effect. Further work is needed to test this hypothesis and explore other possible roles for trophoblast-derived nitric oxide in early pregnancy.

Female↗
PubMed1995

Pre-eclampsia is associated with an excess of proliferative immature intermediate trophoblast.

Pre-eclampsia/toxemia (PET) is an idiopathic hypertensive disorder of pregnancy elicited in susceptible mothers by exposure to placental trophoblast. Three facts regarding the placenta in PET are known: an association with large placentas (excessive trophoblast), a tendency for superficial implantation, and inappropriate trophoblastic immaturity, as assessed by ultrastructural and biochemical criteria. A unitary hypothesis is that PET is related to a maturation defect leading to excessive accumulation of inappropriately immature intermediate trophoblast in the placental implantation site. We studied the implantation site of PET and control placentas from three gestational age groups (25 to 30, 30 to 35, and 36 to 40 weeks old [five per group]) by morphometry and immunohistochemistry using antibodies to three phenotypic markers (cytokeratin, human placental lactogen (HPL), and beta 2-microglobulin) and two markers of cell dynamics (proliferating cell nuclear antigen [PCNA] and bcl-2]). Implantation sites in the PET group had increased amounts of intermediate trophoblast (cell number and longitudinal extent) with an increased proliferative index (percentage of PCNA positive) and evidence of phenotypic immaturity (HPL negative). Intermediate trophoblast from both groups was uniformly bcl-2 negative and beta 2-microglobulin positive. Based on these data and the findings of other investigators, we propose that the diagnostic term "atypical implantation site" be added to acute atherosis, villous infarction, and increased syncytial knotting as a characteristic of placentas from pre-eclamptic pregnancies.

Biomarkers↗
PubMedDate not supplied

Phagocytic properties of cultured murine trophoblast.

The phagocytic potential of cultured trophoblast from early (ectoplacental cone (EPC); day 7.5 post coitum) and mid-term (placenta; day 12 to 14 post coitum) pregnancy in the mouse has been examined using a variety of test particles and culture conditions. In suspension, small numbers (less than 1 per cent) of large placental trophoblast cells showed limited phagocytic uptake of Staphylococcus aureus but not of opsonized sheep red blood cells (RBCs). In contrast, trophoblast phagocytosis was never seen in monolayer placental cell culture. Placental macrophages consistently exhibited phagocytic uptake of both opsonized sheep RBCs and S. aureus under these conditions. In monolayer culture, EPC trophoblast phagocytosed S. aureus, but there was only limited uptake of RBCs (mouse or sheep) or spermatozoa. When cultured in a three-dimensional matrix (blood and plasma clots), however, EPC trophoblast demonstrated extensive phagocytosis of both RBCs and sperm. These results are discussed with reference to the use of in vitro systems for examining developmental processes, and a possible role for trophoblast phagocytosis in early gestation is proposed.

Animals↗
PubMedDate not supplied

Differential expression of blood-group-related carbohydrate antigens by trophoblast subpopulations.

A panel of monoclonal antibodies directed at fucosylated and sialylated carbohydrates on the Type 1 and Type 2 blood group precursor chains was used in an immunohistological study of trophoblast subpopulations. Formalin-fixed paraffin-embedded sections of normal trophoblast throughout pregnancy, hydatidiform moles and gestational choriocarcinoma were examined. Sialyl-Lex was localized in extravillous trophoblast populations in normal and molar pregnancies and choriocarcinoma tumour cells. After neuraminidase treatment, Lex was identified in similar cell populations. Although Lea was identified in syncytial trophoblast cells at the maternofetal interface, no staining was seen for sialyl-Lea. Villous trophoblast did not stain with any of the monoclonal antibodies used. Our results underline the divergent differentiation of trophoblast into villous and invasive extravillous subpopulations. The analogy with tumour cells is discussed.

Antibodies, Monoclonal↗
PubMedDate not supplied

Activities of key enzymes of purine degradation and re-utilization in human trophoblastic cells.

Using density gradient centrifugation, human trophoblastic cells were enriched from mixed cell populations of enzymatically dispersed first- and third-trimester placentae. Over 95 per cent of the cells recovered were of epithelial (i.e., trophoblastic) origin, as evidenced by their cytokeratin intermediate filament positivity and vimentin negativity, examined using indirect immunofluorescence, and also by their high content of human chorionic gonadotrophin. The activities of key enzymes involved in purine degradation and re-utilization (5'-nucleotidase; AMP-deaminase; hypoxanthine phosphoribosyltransferase (HPRT); xanthine dehydrogenase/oxidase) as well as the total activity of alkaline phosphatase were measured in the trophoblastic cells. A six-fold increase in the trophoblastic alkaline phosphatase activity was noted between the first and third trimester. A 40 per cent decrease was noted in the activity of 5'-nucleotidase, which, on the basis of kinetic properties, appears to have a dominant role in the dephosphorylation of placental nucleoside-5'-monophosphates. The trophoblastic activities of AMP-deaminase, HPRT, and xanthine dehydrogenase/oxidase did not change as a function of the gestational age. In view of the relative activities of the latter two enzymes, hypoxanthine formed in the trophoblast appears more likely to be re-utilized than degraded to uric acid.

5'-Nucleotidase↗