Angiotensin-converting enzyme activity and its modulation by oxygen tension in the guinea pig fetal-placental unit

Angiotensin-converting enzyme (ACE) activity in the guinea pig fetal-placental unit was assessed at the different oxygen tensions found in utero, during labor, and at birth. To determine fetal-placental ACE activity, we separately perfused in situ term guinea pig fetuses and their placentas via the umbilical vessels under controlled conditions of flow, temperature, and pH. ACE activity was defined as the percent of angiotensin I (AO) or bradykinin (BK) in Krebs-Henseleit solution cleared by a single passage through the placenta or fetus. Peptide concentrations were measured by radioimmunoassay (RIA). Using BK as substrate, we found that placental and fetal ACE activities were reflected by 45% (SD = 10) and 24% (SD = 7) clearances, respectively, at a perfusate PO2 of 29 mm Hg. Maternal hypoxia (PaO2 = 28 mm Hg) decreased placental ACE activity to 16% (SD = 8) and maternal hyperoxia (PaO2 = 191 mm Hg) increased placental ACE activity to 56% (SD = 9). Using a perfusate PO2 of 95 mm Hg, fetal and placental ACE activity increased in less than 5 minutes to 75% (SD = 10) and 77% (SD = 9), respectively. Similar results were obtained using AI as substrate. We conclude that: fetal-placental ACE activity exhibits a chronically reduced level of activity appropriate to the low oxygen tension found in the fetal-placental unit; the placenta is the primary site of ACE activity in the fetus; maternal oxygenation modulates fetal-placental ACE activity; and fetal ACE activity acutely increases with increased fetal oxygenation and thus may play an important physiological role in the regulation of circulating levels of BK and AII and the circulatory adjustments at birth.     

Expressions of irisin and urotensin II and their relationships with blood pressure in patients with preeclampsia

The aims of this study are to observe irisin and urotensin II (UII) levels in serum and placenta in normal pregnant and preeclamptic women and investigate the relationship between expressions irisin and UII, and their association with blood pressure. A total of 67 pregnant subjects were recruited, including 31 healthy and 36 preeclamptic pregnant women. Serum irisin and UII concentrations were measured. Expressions of fibronectin type III domain-containing protein 5 (FNDC5) (irisin precursor) and UII in placenta specimens were performed. There was no significant difference of serum irisin levels between severe preeclamptic (SPE)) patients, mild preeclamptic (MPE) patients and normal controls, while serum UII was significantly higher in preeclamptic women than normal pregnancy. There was no relationship between serum UII and irisin levels. In patients with preeclampsia, serum irisin was negatively associated with systolic and diastolic blood pressure(r = ?0.350, P = 0.004, r = ?0.307, P = 0.011), while serum UII was positively associated with systolic blood pressure (r = 0.291, P = 0.031). Serum irisin, UII, urinary protein level, BMI and serum creatinine were the independent determinants of blood pressure in preeclampsia by multiple regression analysis. Protein expression of FNDC5 and UII was upregulated in placenta of patients with SPE and positively correlated with systolic blood pressure and urinary protein level. We firstly verify that serum irisin and placental irisin precursor expressions have differently correlated with blood pressure. Expressions of irisin and urotensin II have relationships with blood pressure in patients with preeclampsia     

Activation of local chorionic villi angiotensin II levels but not angiotensin (1-7) in preeclampsia

The chorionic villi in the placenta are responsible for the regulation of fetal oxygen and nutrient transport. Although the peripheral renin-angiotensin system is activated during normal pregnancy, the regulation of the local chorionic villi renin-angiotensin system remains unknown. Therefore, placental chorionic villous tissue was collected from nulliparous third-trimester normotensive or preeclamptic subjects and was analyzed for angiotensin peptide content, angiotensinogen, renin, angiotensin-converting enzyme (ACE), ACE2, neprilysin, angiotensin II type 1 (AT(1)), angiotensin II type 2, Mas receptor mRNAs, and angiotensin receptor density and subtype. Angiotensin II in chorionic villi was significantly higher in preeclamptic subjects, whereas angiotensin (1-7) was not different. Angiotensinogen and AT(1) receptor gene expression was significantly higher in preeclamptic subjects. No differences were observed in renin, ACE, ACE2, or neprilysin gene expression. Mas receptor mRNA in preeclamptic subjects was decreased. The AT(1) receptor was the predominant receptor subtype in normal and preeclamptic chorionic villi. There was no difference in the density of the AT(1,) angiotensin II type 2, and angiotensin (1-7) receptors. These results indicate that enhanced chorionic villous expression of angiotensin II may result from increased angiotensinogen. Elevated angiotensin II, acting through the AT(1) receptor, may favor vasoconstriction in placental chorionic villi and contribute to impaired fetal blood flow and decreased fetal nutrition observed during preeclampsia.     

Lipid metabolism in pregnancy and its consequences in the fetus and newborn

During early pregnancy there is an increase in body fat accumulation, associated with both hyperphagia and increased lipogenesis. During late pregnancy there is an accelerated breakdown of fat depots, which plays a key role in fetal development. Besides using placental transferred fatty acids, the fetus benefits from two other products: glycerol and ketone bodies. Although glycerol crosses the placenta in small proportions, it is a preferential substrate for maternal gluconeogenesis, and maternal glucose is quantitatively the main substrate crossing the placenta. Enhanced ketogenesis under fasting conditions and the easy transfer of ketones to the fetus allow maternal ketone bodies to reach the fetus, where they can be used as fuels for oxidative metabolism as well as lipogenic substrates. Although maternal cholesterol is an important source of cholesterol for the fetus during early gestation, its importance becomes minimal during late pregnancy, owing to the high capacity of fetal tissues to synthesize cholesterol. Maternal hypertriglyceridemia is a characteristic feature during pregnancy and corresponds to an accumulation of triglycerides not only in very low-density lipoprotein but also in low- and high-density lipoprotein. Although triglycerides do not cross the placental barrier, the presence of lipoprotein receptors in the placenta, together with lipoprotein lipase, phospholipase A₂, and intracellular lipase activities, allows the release to the fetus of polyunsaturated fatty acids transported as triglycerides in maternal plasma lipoproteins. Normal fetal development needs the availability of both essential fatty acids and long chain polyunsaturated fatty acids, and the nutritional status of the mother during gestation has been related to fetal growth. However, excessive intake of certain long chain fatty acids may cause both declines in arachidonic acid and enhanced lipid peroxidation, reducing antioxidant capacity.     

Assessment of uterine placental circulation in thrombophilic women

Thrombophilia is associated with several complications of pregnancy including first and second trimester fetal loss, intrauterine fetal death, intrauterine growth restriction, preeclampsia, and placental abruption. Few studies have documented thrombotic lesions observed on the pathologic examination of the placenta in women with severe pregnancy complications. Moreover, a significantly higher rate of factor V Leiden and prothrombin G20210A gene mutations have been found in placentas with thrombotic events compared with normal placentas. In addition, clinical studies have been performed, using Doppler ultrasonography, to assess the uterine placental circulation in women with thrombophilia. Doppler studies of the umbilical artery in cases of intrauterine growth retardation have shown a high systolic to diastolic ratio (S/D) ratio, suggesting an increase in the resistance of the placental small vessels. When these placental vessels were examined after delivery, significant differences were found in comparison with placental vessels of normal pregnancies. Most of the Doppler studies of the umbilical and uterine arteries in pregnancies with thrombophilia were performed in women with antiphospholipid antibodies. The other pathologic conditions associated with thrombophilia and complications of pregnancy were published only recently. These few studies have demonstrated abnormal umbilical and uterine arteries blood flow in complicated pregnancies. Finally, few Doppler studies also suggest improved uterine placental circulation when women with thrombophilia received thromboprophylaxis.     

Reduced expression of corticotropin-releasing hormone receptor type-1 alpha in human preeclamptic and growth-restricted placentas

Placentally derived CRH seems to play a major role in the mechanisms controlling human pregnancy and parturition, via activation of specific receptors widespread in reproductive tissues. In the human placenta, CRH seems to modulate vasodilation, prostaglandin production, and ACTH secretion. It has also been suggested that CRH might act as a placental clock, determining the length of gestation. In addition, maternal plasma CRH concentrations are further elevated in pregnancies associated with abnormal placental function, such as preeclampsia and intrauterine growth retardation (IUGR). In this study, we sought to investigate the expression of CRH-R1 alpha levels in placentas from women who have undergone normal deliveries (control group) and patients who have been diagnosed as having preeclampsia or IUGR. Results showed that placental CRH-R1 alpha mRNA levels (as shown by quantitative RT-PCR) and protein levels (shown by Western blotting analysis) were significantly (P < 0.05) reduced in all of the complicated pregnancies. In contrast, levels of the angiotensin II receptor were elevated in preeclampsia and reduced in IUGR subjects, as shown by RT-PCR and Western blotting analysis. These findings might suggest that changes in receptor expression may contribute toward dysregulation of the dynamic balance controlling vascular resistance.     

Determination of renin, angiotensin converting enzyme and angiotensin II levels in human placenta, chorion and amnion from women with pregnancy induced hypertension

OBJECTIVE  Pregnancy induced hypertension has been shown to be associated with a normal or low activity of the maternal circulating renin–angiotensin system (RAS) but little is known of the local RAS in placenta and fetal membranes. The present study attempts to determine, at full term of human preeclamptic pregnancies, the activity of the chorioplacental renin–angiotensin system.
PATIENTS AND MEASUREMENTS  We analysed the concentrations of active renin, prorenin, angiotensin converting enzyme (ACE) and angiotensin II in homogenates of human placenta and fetal membranes from preeclamptic patients at full term pregnancy. The values of renin, ACE and angiotensin II found in the patients with moderate preeclampsia (gestosis index 0–1) ( n  = 10) were compared with those of normal pregnant women ( n  = 8).
RESULTS  Our experiments showed that in preeclamptic pregnancies, the chorion membrane contained the highest concentrations of active renin (2905 ± 152 pg/g, mean ± SD), prorenin (21 315 ± 2849 pg/g) and ACE (1258 ± 302 U/g) whereas the placenta had more angiotensin II than the chorion and amnion (741 ± 45 vs 456 ± 40 and 428 ± 64 pg/g, respectively). In the placenta, as in the fetal membranes, no significant difference was found in the levels of active renin, ACE or angiotensin II between hypertensive patients and normal subjects but a slightly lower level of chorionic prorenin ( P  < 0.05) was observed in pregnancy induced hypertension.
CONCLUSION  These findings indicate that in moderate preeclampsia (gestosis index 0–1), the activity of the renin–angiotensin system in term human placenta and fetal membranes remains essentially normal.     

Exogenous vascular endothelial growth factor can induce preeclampsia-like symptoms in pregnant mice

It is reported that expression of vascular endothelial growth factor (VEGF) in trophoblasts increases in cases with preeclampsia. Recently, we demonstrated that the lack of cyclin-dependent kinase inhibitor, p57kip2, expression in the fetus and the placenta plays a role in the development of preeclampsia-like symptoms in pregnant mice. Furthermore, we observed that VEGF mRNA and protein levels, especially VEGF (164), were higher and its expression was stronger in placentas of p57kip2-null embryos than in placentas of wild-type embryos. In this study we investigated whether exogenous murine VEGF (164) induced preeclampsia-like symptoms in pregnant mice, and anti-VEGF neutralized antibody could suppress these symptoms. Administration of VEGF induced hypercoagulation in the placental circulation and a significant elevation of systolic blood pressure in pregnant mice. Furthermore, we demonstrated that treatment with anti-VEGF antibody could suppress the hypercoagulability in placenta and the elevation of systolic blood pressure. These data suggest that VEGF is related to the pathophysiology of preeclampsia.     

Dysregulation of the circulating and tissue-based renin-angiotensin system in preeclampsia

The renin-angiotensin system (RAS) participates in preeclampsia; however, the relative contributions from the circulating RAS and the tissue-based, uteroplacental RAS are unknown. We hypothesized that the tissue-based uteroplacental RAS is dysregulated in preeclampsia. We performed microarray and gene expression studies and confirmed the findings on the protein level by immunohistochemistry in ureteroplacental units from 10 preeclamptic women and 10 women with uneventful pregnancies. All of the women were delivered by cesarean section. We also analyzed plasma renin activity and circulating agonistic angiotensin II type 1 (AT1) receptor autoantibodies. In preeclampsia, we found that the angiotensin II AT1 receptor gene was 5-fold upregulated in decidua (maternal origin). We also found AT1 autoantibodies in preeclamptic women and in their offspring by neonatal cardiomyocyte bioassay compared with women with normal pregnancies and their infants (mother: 17.5+/-2.2 versus 0.05+/-0.4; fetus: 14.5+/-1.8 versus 0.5+/-0.5 Deltabpm). Gene expressions for renin (35.0-fold), angiotensin-converting enzyme (2.9-fold), and angiotensinogen (8.9-fold) were higher in decidua than placenta (fetal origin) in both control and preeclamptic women, whereas the AT1 receptor was expressed 10-fold higher in placenta than in decidua in both groups. Our findings elucidate the ureteroplacental unit RAS in preeclamptic and normal pregnancies. We found that, in preeclampsia, the AT1 receptor expression is particularly high in decidua, combined with pregnancy-specific tissue RAS involving decidual angiotensin II production and AT1 autoantibodies. We also showed that AT1 autoantibodies cross the ureteroplacental barrier. These components could participate in the pathophysiology of preeclampsia.     

Excretion of biliary compounds during intrauterine life

In adults, the hepatobiliary system, together with the kidney, constitute the main routes for the elimination of several endogenous and xenobiotic compounds into bile and urine, respectively. However, during intrauterine life the biliary route of excretion for cholephilic compounds, such as bile acids and biliary pigments, is very poor. Although very early in pregnancy the fetal liver produces bile acids, bilirubin and biliverdin, these compounds cannot be efficiently eliminated by the fetal hepatobiliary system, owing to the immaturity of the excretory machinery in the fetal liver. Therefore, the potentially harmful accumulation of cholephilic compounds in the fetus is prevented by their elimination across the placenta. Owing to the presence of detoxifying enzymes and specific transport systems at different locations of the placental barrier, such as the endothelial cells of chorionic vessels and trophoblast cells, this organ plays an important role in the hepatobiliary-like function during intrauterine life. The relevance of this excretory function in normal fetal physiology is evident in situations where high concentrations of biliary compounds are accumulated in the mother. This may result in oxidative stress and apoptosis, mainly in the placenta and fetal liver, which might affect normal fetal development and challenge the fate of the pregnancy. The present article reviews current knowledge of the mechanisms underlying the hepatobiliary function of the fetal-placental unit and the repercussions of several pathological conditions on this tandem.     

Effect of a low calcium intake on the vascular sensitivity to angiotensin II in normotensive pregnant rats.

Vascular responsiveness to angiotensin II in pregnant rats with a normal or a low calcium diet were examined. From day 6 of pregnancy, Wistar rats were separated into two groups. One group was fed a normal diet containing 1.2% calcium (control group) and the other group was fed a low calcium diet containing 0.02% calcium (low Ca group). Using a tail cuff method, the systolic blood pressure in the low Ca group was found to be significantly higher than that in the control group on day 18 of pregnancy. On days 12 and 18 of pregnancy using the hindquarters perfusion technique, the vascular response to bolus angiotensin II (30, 100, 300, and 1000 ng/kg of rat body weight) in the low Ca group increased significantly more than that in the control group. However, the pressor response to norepinephrine and the depressor response to acetylcholine did not differ between the low Ca group and the control group. Urinary sodium excretion in the low Ca group was lower than that in the control group on days 12 and 18 of pregnancy, and decreased toward term, whereas urinary phosphorus excretion in the low Ca group was higher than that in the control group on days 12 and 18 of pregnancy. These data indicate that low calcium intake during pregnancy increases sensitivity to the pressor effects of angiotensin II and increases systolic blood pressure in normotensive pregnant rats.     

Hypertension in pregnancy

Hypertension in pregnancy is diagnosed on systolic blood pressure greater than or equal to 140 mm Hg and/or diastolic greater than or equal to 90 mm Hg. The classification systems separate chronic and gestational hypertension from preeclampsia. Significant uncertainty regarding optimal management is reflected in the differing major international society recommendations. Blood pressure treatment is designed to minimize maternal end-organ damage. Methyldopa, labetalol, hydralazine, and nifedipine are oral options; angiotensin-converting enzyme inhibitors and angiotensin receptor antagonists are contraindicated. Women with preeclampsia should be closely monitored and receive intravenous magnesium sulfate.     

Multiple factors contribute to the pathogenesis of hypertension in Cushing's syndrome

The mechanisms causing high blood pressure in patients with Cushing's syndrome were investigated by measurements of humoral factors and pharmacological maneuvers. Twelve patients with adrenal adenomas were studied. The mean systolic and diastolic pressures of the patients were 171 +/- 28 and 109 +/- 15 mm Hg (+/- SEM), respectively, which were significantly higher than those of normal subjects. PRA, plasma renin concentration, plasma renin substrate, plasma cortisol, plasma aldosterone, urinary kallikrein, and urinary prostaglandin E2 were measured as the humoral factors. PC values were markedly elevated in patients with Cushing's syndrome. Among the components of the renin-angiotensin system, only plasma renin substrate was increased. Urinary kallikrein and prostaglandin E2 were decreased in patients with Cushing's syndrome. Oral administration of captopril lowered blood pressure, but infusion of an angiotensin II analog did not. Furthermore, the pressor responses to infusion of both norepinephrine and angiotensin II were increased. We conclude that blood pressure is elevated in patients with Cushing's syndrome because they have enhanced pressor responses to vasoactive substances, suppression of depressor systems, and some abnormalities of the renin-angiotensin system.     

Clinical use of placental hormones in pregnancy management

Across human pregnancy, placenta represents a transit of oxygen and nutrients from the mother to the fetus and actively produces a large number of hormones that serve to regulate and balance maternal and fetal physiology. An abnormal secretion of placental hormones may be part of the pathogenesis of the main obstetric syndrome, from early to late pregnancy, in particular chromosomopathies, miscarriage, gestational trophoblastic diseases, preeclampsia, gestational diabetes, and pre-term delivery. The possibility to measure placental hormones represents an important tool not only for the diagnosis and management of gestational disorders, but it is also fundamental in the early identification of women at risk for these pregnancy complications. In the last decades, the use of ultrasound examination has provided additional biophysical markers, improving the early diagnosis of gestational diseases. In conclusion, while few placental hormones have sufficient sensitivity for clinical application, there are promising new biochemical and biophysical markers that, if used in combination, may provide a valid screening tool.     

Transplacental transfer of human antinuclear antibodies in mice by injection of lupus IgG in pregnant animals

Pregnant female Balb/c mice were injected with IgG fractions from patients with systemic lupus erythematosus, in order to study the in vivo passage of antinuclear antibodies (ANA) across the placenta. After injection of monospecific sera directed against nDNA, Sm, nRNP, Ro(SSA) and La(SSB), ANA were found in fetal circulation and trapped in the liver, spleen kidney and skin of fetus. Also, ANA were demonstrated in placental tissue and cord. The placental IgG-Fc receptors apparently played a major role in ANA entry into the fetus. Our study demonstrates that human ANA can be passively transferred into experimental animals to study their kinetics during pregnancy.     

Low serine hydroxymethyltransferase activity in the human placenta has important implications for fetal glycine supply

Glycine is essential for fetal development, but in both sheep and human pregnancy, little is transported directly from the mother to the fetus, indicating that fetal glycine is derived from other sources. In the sheep, placental conversion of maternal serine by serine hydroxymethyltransferase (SHMT) provides almost all the glycine transported to the fetus. Although mRNA for mitochondrial and cytoplasmic SHMT has been detected in human placenta, it is not known whether substantial placental conversion of serine to glycine occurs in species other than sheep. We determined SHMT activity in human, rat, and sheep placenta by measuring conversion of [3-(14)C]serine to (14)C-methylene tetrahydrofolate. Compared with term human placenta, SHMT activity per gram of placenta was 5.1-fold higher in term rat placenta and 24.1-fold higher in term sheep placenta. In sheep placenta, SHMT activity per gram of placenta increased 2.1-fold between mid-gestation and term. In human placenta, placental SHMT activity was similar 8 wk post conception and at term. The low activity of SHMT in the human and rat placenta suggests that, unlike in the sheep, placental conversion of serine to glycine is not a major source of fetal glycine in these species.     

The effect of angiotensin II on platelet intracellular free calcium concentration in human pregnancy.

OBJECTIVES: The primary objective of this study was to determine the effect of i.v. angiotensin II infusion on platelet intracellular free calcium concentration in potentially hypertensive primigravid women. DESIGN: Patients at 28-32 weeks gestation were selected on the basis of a diastolic pressure less than or equal to 80 mmHg taken at the antenatal clinic visit. METHODS: An angiotensin II infusion test (4-16 ng/kg per min) was performed in 13 women. Platelet intracellular free calcium concentration, platelet angiotensin II binding site density and plasma angiotensin II concentration were measured before and at the end of the infusion. Pregnancy outcome (normotension or hypertension) was recorded. RESULTS: Platelet intracellular free calcium concentration rose in 12 of 13 women during angiotensin II infusion. This rise was not directly correlated with initial or final platelet angiotensin II binding site density, plasma angiotensin II concentration or the evoked change in systolic or diastolic blood pressure. Five women subsequently developed pregnancy-induced hypertension. Although basal platelet intracellular free calcium concentration did not differ between the two groups, platelet intracellular free calcium concentration rose twice as much in response to angiotensin II in the five hypertensive pregnant women. There was a 12-fold increase in platelet angiotensin II binding in the future hypertensives, although basal angiotensin II was the same in the two groups. CONCLUSION: The enhanced rise in platelet intracellular free calcium concentration in response to angiotensin II administration in women who subsequently became hypertensive, together with their increased angiotensin II binding site density suggest a possible enhanced stimulus-effect coupling. Pregnancy-induced hypertension is a state of marked vasoconstriction, with an enhanced pressor response to angiotensin II. These data supply grounds for a hypothesis concerning the mechanism.     

Understanding vitamin D metabolism in pregnancy: From physiology to pathophysiology and clinical outcomes

This critical time frame of intrauterine life development is considered of major importance on the metabolic imprinting of overall health of the offspring, in later life. This requires a delicate immune balance that nurtures the allogeneic fetus, while maintaining reactivity against pathogens. Dysregulation of these tightly controlled biophenomena at a systemic and placental level, have been considered as a potential mechanism mediating pathogenesis of preeclampsia and spontaneous birth. In this context, vitamin D has been considered as a significant regulator of both innate and adaptive immunity by regulating cell proliferation, differentiation and apoptosis.Vitamin D metabolism during pregnancy manifests striking differences as compared to the non-pregnant state. Calcitriol is increasing > 2–3 fold in the first weeks of pregnancy whereas maternal 25-hydroxyvitamin D crosses the placental barrier and represents the main pool of vitamin D in the fetus. Moreover, during pregnancy, vitamin D receptor and regulatory metabolic enzymes are expressed in the placenta and decidua, indicating a potential critical point in the immunomodulation at the maternal-fetal interface. Considering these effects, maternal hypovitaminosis D during pregnancy has been associated with pregnancy related disorders. This review focuses on the mechanistic basis of these adaptive changes, as a background for the development of pregnancy related disorders, with a discourse on the pathophysiology relating hypovitaminosis D and clinical outcomes.