Stem villous arteries from the placentas of heavy smokers: functional and mechanical properties

Smoking for two- effects of tobacco consumption on placenta

Tobacco smoking is an important public health issue recognized by the world health organization as one of the most serious, preventable risk factors for developing a series of pregnancy pathologies. Maternal smoking is positively associated with intrauterine growth restriction (IUGR) and gestational diabetes (GDM), but negatively associated with preeclampsia (PE). In this review, we examine epidemiological, clinical and laboratory studies of smoking effects on immunoregulation during pregnancy, trophoblast function, and placental vasculature development and metabolism. We aim to identify effects of tobacco smoke components on specific placental compartments or cells, which may contribute to the understanding of the influences of maternal smoking on placenta function in normal and pathological pregnancies. Data corroborates that in any trimester, smoking is unsafe for pregnancy and that its detrimental effects outweigh questionable benefits. The effects of maternal smoking on the maternal immune regulation throughout pregnancy and the impact of different tobacco products on fetal growth have not yet been fully understood. Smoking cessation rather than treatment with replacement therapies is recommended for future mothers because also single components of tobacco and its smoke may have detrimental effects on placental function.

Tobacco Smoking During Pregnancy Is Associated With Increased Risk of Moderate/Severe Bronchopulmonary Dysplasia: A Systematic Review and Meta-Analysis

Epidemiological evidence and animal studies support that intrauterine exposure to tobacco smoke disturbs lung development and has a negative effect in the pulmonary health of the offspring. Individual studies suggest an association between fetal exposure to maternal smoking and risk of developing bronchopulmonary dysplasia (BPD). However, this association has not yet been systematically investigated. We aimed to conduct a systematic review of studies reporting on tobacco smoking during pregnancy as potential risk factor for BPD. PubMed/MEDLINE and EMBASE databases were searched. BPD was defined as requirement of supplemental oxygen on postnatal day 28 (BPD28; all BPD), at the postmenstrual age (PMA) of 36 weeks (BPD36; moderate/severe BPD), or as requirement of more than 30% oxygen and/or positive pressure at 36 weeks PMA (severe BPD). Pooled risk ratios (RR) and 95% confidence intervals (CI) were calculated using a random-effects model. Of 2,894 potentially relevant studies, 33 met the inclusion criteria. The included studies evaluated 171,772 infants and included 30,445 cases of exposure to maternal smoking and 25,340 cases of BPD of any severity. Meta-analysis showed a significant association between tobacco smoking during pregnancy and BPD36 (17 studies, RR 1.126, 95% CI 1.008-1.259, p = 0.036), but could not demonstrate a significant association between tobacco smoking during pregnancy and BPD28 (16 studies, RR 1.021, 95% CI 0.924-1.129, p = 0.681), or severe BPD (3 studies, RR 1.143, 95% CI 0.528-2.478, p = 0.734). In conclusion, our data suggest that tobacco smoking during pregnancy increases the risk of moderate/severe BPD. Our results highlight the detrimental effects of tobacco smoking and reinforce the hypothesis of the involvement of prenatal insults in the etiopathogenesis of BPD.

Pharmacological profile of vascular activity of human stem villous arteries

INTRODUCTION

The function of the placental vasculature differs considerably from other systemic vascular beds of the human body. A detailed understanding of the normal placental vascular physiology is the foundation to understand perturbed conditions potentially leading to placental dysfunction.

METHODS

Behaviour of human stem villous arteries isolated from placentae at term pregnancy was assessed using wire myography. Effects of a selection of known vasoconstrictors and vasodilators of the systemic vasculature were assessed. The morphology of stem villous arteries was examined using IHC and TEM.

RESULTS

Contractile effects in stem villous arteries were caused by U46619, 5-HT, angiotensin II and endothelin-1 (p ≤ 0.05), whereas noradrenaline and AVP failed to result in a contraction. Dilating effects were seen for histamine, riluzole, nifedipine, papaverine, SNP and SQ29548 (p ≤ 0.05) but not for acetylcholine, bradykinin and substance P.

DISCUSSION

Stem villous arteries behave differently to vessels of the systemic vasculature and results indicate that the placenta is cut off from the systemic maternal vascular regulation. Particularly, endothelium-dependent processes were attenuated in the placental vasculature, creating a need to determine the role of the endothelium in the placenta in future studies.

Prolonged endoplasmic reticulum stress alters placental morphology and causes low birth weight

The role of endoplasmic reticulum (ER) stress in pregnancy remains largely unknown. Pregnant mice were subcutaneously administered tunicamycin (Tun), an ER stressor, as a single dose [0, 50, and 100 μg Tun/kg/body weight (BW)] on gestation days (GDs) 8.5, 12.5, and 15.5. A high incidence (75%) of preterm delivery was observed only in the group treated with Tun 100 μg/kg BW at GD 15.5, indicating that pregnant mice during late gestation are more susceptible to ER stress on preterm delivery. We further examined whether prolonged in utero exposure to ER stress affects fetal development. Pregnant mice were subcutaneously administered a dose of 0, 20, 40, and 60 μg Tun/kg from GD 12.5 to 16.5. Tun treatment decreased the placental and fetal weights in a dose-dependent manner. Histological evaluation showed the formation of a cluster of spongiotrophoblast cells in the labyrinth zone of the placenta of Tun-treated mice. The glycogen content of the fetal liver and placenta from Tun-treated mice was lower than that from control mice. Tun treatment decreased mRNA expression of Slc2a1/glucose transporter 1 (GLUT1), which is a major transporter for glucose, but increased placental mRNA levels of Slc2a3/GLUT3. Moreover, maternal exposure to Tun resulted in a decrease in vascular endothelial growth factor receptor-1 (VEGFR-1), VEGFR-2, and placental growth factor. These results suggest that excessive and exogenous ER stress may induce functional abnormalities in the placenta, at least in part, with altered GLUT and vascular-related gene expression, resulting in low infant birth weight.

Morphological and biological effects of maternal exposure to tobacco smoke on the feto-placental unit

Active and passive maternal smoking has a damaging effect in every trimester of human pregnancy. Cigarette smoke contains scores of toxins which exert a direct effect on the placental and fetal cell proliferation and differentiation and can explain the increased risk of miscarriage, fetal growth restriction (FGR) stillbirth, preterm birth and placental abruption reported by epidemiological studies. In the placenta, smoking is associated from early in pregnancy, with a thickening of the trophoblastic basement membrane, an increase in collagen content of the villous mesenchyme and a decrease in vascularisation. These anatomical changes are associated with changes in placental enzymatic and synthetic functions. In particular, nicotine depresses active amino-acid (AA) uptake by human placental villi and trophoblast invasion and cadmium decreases the expression and activity of 11 beta-hydroxysteroid dehydrogenase type 2 which is causally linked to FGR. Maternal smoking also dysregulates trophoblast expression of molecules that govern cellular responses to oxygen tension. In the fetus, smoking is associated with a reduction of weight, fat mass and most anthropometric parameters and as in the placenta with alterations in protein metabolism and enzyme activity. These alterations are the results of a direct toxic effect on the fetal cells or an indirect effect through damage to, and/or functional disturbances of the placenta. In particular, smoking interferes strongly with the fetal brain and pancreas biological parameters and induces chromosomal instability, which is associated with an increase in the risk of cancer, especially childhood malignancies.

The human placenta from heavy smokers: evaluation of vasoactive peptides by immunohistochemistry

The study aimed to demonstrate the expression of nitric oxide converting enzyme, nitric oxide synthase (e-NOS), and endothelin-1 (Et-1) in formalin-fixed paraffin-embedded placental tissue, and to demonstrate a difference in staining intensity between heavy smokers and non-smokers. Term placentas from pregnancies from otherwise healthy women smoking 15 or more cigarettes per day (heavy smokers) and term placentas from a matching group of non-smokers were included. The antibodies for Et-1 and e-NOS are recommended for cryostat sections. We evaluated the antibodies on paraffin-embedded tissue combined with the streptavidin-biotin-peroxidase technique. Et-1 and e-NOS were demonstrated in the placental vasculature, the trophoblast, and the amnion. A blinded comparative study showed no reproducible significant differences in the staining intensity of the antigen-antibody reaction to Et-1 and e-NOS between the two groups.

The effects of smoking and hypertensive disorders on fetal growth

Background

It is well known that smoking and pregnancy induced hypertension (PIH) are associated with decreased fetal growth. It has been reported that in preeclampsia the fetal growth deficit attributable to smoking is higher, which has been contradicted in other studies. We therefore evaluated the effects on fetal growth of early- and late onset PIH and chronic hypertension and how cigarette smoking modify these effects. We also quantified the proportion of small for gestational age (SGA) cases attributable to PIH, chronic hypertension, and smoking.

Methods

Population-based study based on record of 215598 singleton pregnancies from the Medical Birth Registry of Norway.

Results

In severe preeclampsia, mild preeclampsia, transient hypertension, and normotension in term birth, odds ratios (ORs) of SGA in smokers compared with non-smokers were 1.4 (95% confidence interval 0.9, 2.2), 1.6 (1.3, 1.9), 2.3 (1.8, 3.1), and 2.0 (1.9, 2.1), respectively. For preterm births, corresponding ORs were 1.3 (0.9, 2.0), 1.8 (1.1, 3.0), 4.1 (1.9, 9.0), and 1.7 (1.4, 2.0), respectively. The effect of early onset PIH was stronger than that in term births, while the effect of smoking was equal in preterm and term newborns. Only in non-smokers who delivered at term, the rates of SGA significantly increased with the severity of PIH (ORs = 1.3 (1.1, 1.5), 1.8 (1.7, 2.0), and 2.5 (2.2, 3.0) for transient hypertension, mild-, and severe preeclampsia, respectively). The combined effects of smoking and hypertension were generally not synergistic. The effect of smoking was not stronger in women who had chronic hypertension. Nor were the effects of chronic hypertension stronger in smokers. PIH explained 21.9 and 2.5% of preterm and term cases of SGA, respectively, while smoking explained 12% of SGA cases.

Conclusion

The effects of hypertensive disorder and smoking were generally not synergistic, which suggest that they may exert their main actions on separate sites or work through separate mechanisms within or outside the placenta. If smoking were eliminated in pregnant women, the number of SGA cases would be reduced by 12%.

Sphingosine-1-Phosphate Acts via Rho-Associated Kinase and Nitric Oxide to Regulate Human Placental Vascular Tone1

Sphingosine-1-phosphate (S1P), a bioactive lipid released from activated platelets, has been demonstrated in animal models to regulate vascular tone through receptor-mediated activation of Rho-associated kinase 1 and nitric oxide synthase 3. The role of S1P in regulation of human vascular tone (particularly during pregnancy, with its unique vascular adaptations and localized platelet activation) is unknown. We hypothesized that S1P would constrict small placental arteries through activation of Rho-associated kinases with modulation by nitric oxide. Reverse transcription-polymerase chain reaction of chorionic plate artery preparations detected mRNAs encoding all five receptors for S1P, and S1P induced dose-dependent vasoconstriction of both chorionic plate and stem villous isobarically mounted arteries, which at 10 micromol/L was 32.9% +/- 3.86% (mean +/- SEM) and 34.6% +/- 7.01%, respectively. In stem villous arteries, S1P-induced vasoconstriction was enhanced significantly following inhibition of nitric oxide synthases with N(G)-nitro-L-arginine methyl ester (100 micromol/L, 52.6% +/- 6.28%, P < 0.05). The S1P-induced vasoconstriction was reversed by Y27632, an inhibitor of Rho-associated kinases (10 micromol/L) in both chorionic plate (to 14.9% +/- 4.95%) and stem villous arteries (to 2.71% +/- 6.13%). The S1P added to alpha-toxin-permeabilized, isometrically mounted chorionic plate arteries bathed in submaximal Ca(2+)-activating solution induced Ca(2+)-sensitization of constriction, which was 47.7% +/- 10.0% of that occurring to maximal Ca(2+)-activating solution. This was reduced by Y27632 to 18.4% +/- 18.4%. Interestingly, S1P-induced vasoconstriction occurred in all isobarically mounted arteries but was inconsistent in isometrically mounted chorionic plate arteries. In summary, S1P-induced vasoconstriction in human placental arteries is mediated by increased Ca(2+)-sensitization through activation of Rho-associated kinases, and this vasoconstriction also is modulated by nitric oxide. Identification of these actions of S1P in the placental vasculature is important for understanding both normal and potentially abnormal vascular adaptations with pregnancy.

Maternal smoking and causes of very preterm birth

BACKGROUND

Smoking increases the risk of preterm birth. The present study was made to elucidate the relation of smoking to causes of very preterm birth.

METHODS

In a case-control study on all very preterm births in two regions of Stockholm 1988-1992, prospectively collected data were extracted from antenatal and delivery records on smoking, other maternal characteristics, pregnancy complications, and causes of preterm birth. Cases were live single births with a gestational age of < or =32 weeks and 0 days, and controls were live singletons delivered at 37 weeks or later (n = 295, respectively). Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated with logistic regression.

RESULTS

Compared with non-smokers, adjusted ORs of very preterm birth among moderate smokers (1-9 cigarettes per day) and heavy smokers (> or =10 cigarettes per day) were 1.4 (95% CI 0.8-2.4) and 2.9 (95% CI 1.5-5.7), respectively. Compared with non-smokers, risk of preterm labor was increased among moderate and heavy smokers [ORs 1.9 (95% CI 1.0-3.6) and 2.6 (95% CI 1.1-1.6), respectively]. These risks remained essentially unchanged in women without an identifiable cause of preterm labor ('idiopathic preterm labor'). Smoking was also associated with dose-dependent increases in risks of preterm birth due to preterm premature rupture of membranes and late pregnancy bleedings. There was no association between smoking and risk of very preterm birth caused by hypertensive diseases.

CONCLUSIONS

Smoking increases the risk of very preterm birth caused by preterm labor (including idiopathic preterm labor), preterm premature rupture of membranes, and late pregnancy bleedings.

Metals content in placentas from moderate cigarette consumers: correlation with newborn birth weight

Cigarette consumption during pregnancy produces deleterious effects in both, mother and fetus, some of them due to the presence of toxic elements in cigarette smoke, such as cadmium. Placenta constitutes a dual-purpose specimen for evaluating the pollutant burden exerted on the mother as well as on the fetus. The main objective of this study was to establish a correlation between placental concentration and distribution of some metal elements and birth weight of neonates delivered by mothers, who were either moderate smokers or nonsmokers. Forty nonsmoking and moderate smoking pregnant women paired per age, parity, weight, height and body mass index were selected. Smoking was assessed by self-reported cigarette consumption during pregnancy and urine cotinine concentration before delivery. Placental metal concentrations were evaluated by atomic absorption spectrometry (copper and cadmium) and neutron activation analysis (zinc and iron). Newborns from smokers had lower birth weights compared to infants from nonsmokers. Birth weights were correlated with placental cadmium concentrations in both, smokers and nonsmokers. Placental zinc and cadmium of smokers were mainly located at the maternal side and their levels were higher than those found in nonsmoker's placentas. In addition, all metal nutrient/pollutant ratios were decreased in the smoker group. In this first study performed in our region, we found that moderate smoking mothers deliver neonates with decreased birth weight and highly correlated to placental cadmium concentration. Decreased metal nutrient/pollutant ratios, a condition here found in smokers, may indicate a placental dysfunction, contributing to impair birth weight.

Direct placental effects of cigarette smoke protect women from pre-eclampsia: the specific roles of carbon monoxide and antioxidant systems in the placenta

Pre-eclampsia is a hypertensive disorder of pregnancy characterized by shallow placentation, inadequate placental perfusion, localized placental oxidative stress, a heightened maternal inflammatory response and subsequent maternal endothelial dysfunction. This pathophysiology leads to an increase in maternal blood pressure, edema and proteinurea. Interestingly, women who smoke cigarettes throughout pregnancy are at a 33% reduced risk of developing this disorder. The exact mechanisms through which cigarette smoke reduces the risk of pre-eclampsia are not yet understood. We propose that cigarette smoke reduces the risk of developing pre-eclampsia via direct placental effects. In this review we will address, and provide evidence for, our specific hypotheses that: (a) CO increases trophoblast invasion and spiral arteriole remodeling; (b) CO decreases a localized inflammatory response at the level of the decidua; (c) CO increases utero-placental, intra-placental and feto-placental blood flow; (d) CO decreases hypoxia-induced apoptosis of the syncitiotrophoblast layer; (e) CO activates hemoproteins involved in normal endothelial functioning normally acted upon by NO; (f) compound(s) within cigarette smoke result in upregulation of antioxidant systems within the placenta. These various mechanisms of action must be further examined as they may provide valuable keys to novel therapeutic design in the realm of pre-eclampsia research.

Aspects of human fetoplacental vasculogenesis and angiogenesis. III. Changes in complicated pregnancies

Patterns of fetoplacental angiogenesis vary not only during the course of a normal pregnancy but also in certain pregnancy pathologies. Here, we review some of the molecular and morphological events which occur in complicated pregnancies. The pregnancy complications are chosen in an attempt to represent the possible different origins (preplacental, uteroplacental, postplacental) of fetal hypoxia. Molecular events focus on reported changes in hypoxia-inducible factors, angiopoietins and the vascular endothelial, basic fibroblast and placenta growth factors and their receptors. Morphological changes focus on patterns of angiogenesis (branching and non-branching) and a consistent set of morphometric descriptors (covering measures of total capillary growth, villous capillarization and capillary size and shape in transverse section). Apart from some uncertainties due to lack of information, or failure to resolve fully the effects of intrauterine growth restriction and pre-eclampsia, alterations in the angiogenic growth factors and morphologies of capillaries and villi in different complicated pregnancies seem to conform reasonably well to those predicted by the fetal hypoxia paradigm. However, it is clear that future studies on the effects of different origins of fetal hypoxia should exercise more care in the choice and interpretation of relevant descriptors and take more account of the parallel effects of possible confounders. In addition, rather than comparing uncomplicated and complicated pregnancies only at term, more information about molecular and morphological events that occur throughout gestation would be extremely valuable. This includes further studies on changes in growth factor receptors, the less-well-documented angiogenic factors (e.g. angiogenin, angiostatin, endostatin) and the associations between endothelial cells and pericytes. A more integrated approach involving also parallel analysis of the effects of erythropoietin and other potential vasoactive factors on the behaviour and morphology of fetal vessels would be beneficial.

Vascular reactivity of the preplacental vasculature in Guinea pigs

The functional correlates of structural remodelling of the preplacental arteries are not well known. We examined the responses of these vessels to vasoactive agents in guinea pigs at mid and late gestation, and attempted to relate them to changes in vessel structure. Segments were taken from the arcade artery, a mesometrial artery near its origin, and an artery near the placenta. They were mounted as rings in a myograph and concentration-response curves were obtained for U46619, endothelin-1 and arginine vasopressin. The vessel segments were then examined by histology and immunohistochemistry. Trophoblast was identified as immunopositive for cytokeratin, circular muscle stained positive for muscle actin and smooth muscle actin, and presumed myofibroblasts in the adventitial layer stained positive only for smooth muscle actin. At both gestational ages, arcade and mesometrial arteries had intact vessel walls. Midgestation placental arteries were characterized by partial or complete disruption of the internal elastic lamina and the presence of a large number of myofibroblasts and of periarterial trophoblast. In late pregnancy, the changes were more extensive, with almost complete dedifferentiation of the smooth muscle cells and trophoblast invasion of the adventitial layer. From midgestation to late gestation, the responses of placental arteries to U46619, endothelin-1 and arginine vasopressin, normalized to the response to K(+)depolarization, were significantly reduced. This suggests that the extensive changes in wall structure in late gestation, which accompany trophoblast invasion, modulate the responses of these vessels to vasoconstrictors. However, mesometrial arteries also demonstrated reduced responsiveness to U46619, suggesting the influence of factors other than trophoblast.

Altered protein profile and possible hypoxia in the placenta of 2,3,7,8-tetrachlorodibenzo-p-dioxin-exposed rats

Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) during pregnancy causes fetal death in many animal species. In an earlier study we observed alteration of placental glucose kinetics at the same TCDD exposure level that resulted in fetal death (Ishimura et al., Toxicol. Appl. Pharmacol. 178, 161-171, 2002). In the present study, in order to identify the molecules that might explain the alterations of placental function and the mechanism of fetal death, we used two-dimensional gel electrophoresis (2D/E) to detect and identify placental proteins whose amounts changed after exposure to TCDD and we examined the expression properties of these proteins in the placenta during hypoxia by using the uterine artery ligation model. Pregnant Holtzman rats were given a single oral dose of 1600 ng TCDD/kg body wt or an equivalent volume of vehicle (control) on gestational day (GD) 15 and placental tissue was collected on GD16 and GD20. The 15,000 g supernatant fractions of placental homogenates from the control group and TCDD-exposed group were subjected to the 2D/E analysis, and the protein spots whose amounts had changed after exposure to TCDD were characterized by amino acid sequence analysis. The amounts of heat shock protein 27 (Hsp27) and beta-tropomyosin (beta-TM) in TCDD-exposed placentas tended to have increased on GD16 and had increased significantly on GD20, and these changes were followed by an approximately twofold increase in glyceraldehyde 3-phosphate dehydrogenase (GAPDH) on GD20. Next, the uterine-artery ligation model was prepared on GD15, and the hypoxic placentas were collected on GD20. Two-D/E analysis of the 15,000 g supernatant proteins of the placentas revealed an increased level of GAPDH but not of other proteins, including Hsp27 and beta-TM. The results of this study showed that the increase in GAPDH level during hypoxia previously observed in endothelial cells occurs in the placenta and indicated that the TCDD-exposed placentas were in a hypoxic state at the end of pregnancy. Finally, the results of this study suggested the possibility that the increased incidence of fetal death after exposure to TCDD was due to the placental hypoxia.

Stereologic examination of placentas from mothers who smoke during pregnancy

OBJECTIVE

Structural changes in the placenta might contribute to the lower birth weight seen among infants born to mothers who smoke cigarettes. In this study, a morphologic examination and a stereologic quantitation of placentas from mothers who smoked cigarettes and who did not smoke cigarettes during pregnancy were performed.

STUDY DESIGN

Twenty-five placentas from mothers who did not smoke cigarettes, 15 placentas from mothers who smoked 5 to 10 cigarettes per day, 16 placentas from mothers who smoked 11 to 20 cigarettes per day, and 16 placentas from mothers who smoked >20 cigarettes per day were delivered at term after normal pregnancies and were fixed by dual perfusion. The volume and the surface area of villi, the trophoblast volume, and the volume and the surface area and length of villous capillaries were estimated. A measurement of the concentration of cadmium in serum was used to assess the validity of information concerning smoking habits.

RESULTS

No differences were shown in the total volume of placenta between the groups. The estimated volume and surface area and the calculated lengths for villous capillaries were significantly reduced in all 3 groups of smokers. A significant increase of the trophoblast volume was observed in the mothers who smoked cigarettes.

CONCLUSION

Cigarette smoking during pregnancy influences the placental vasculature. The reduced dimensions of fetal capillaries in villi may affect the placental blood flow, and the diminished area for exchange of gases and nutrients between the mother and the fetus will increase the risk of fetal undernourishment.

Placental cadmium and progesterone concentrations in cigarette smokers

Cadmium and progesterone concentrations were evaluated in term placentas collected from 56 healthy parturients in the city of Zagreb. Concentrations of lead, iron, zinc, and copper in placentas were analyzed. Data collected by questionnaire identified 29 nonsmoking and 27 smoking women. From each placenta, three samples from different locations were taken. Metals were measured by atomic absorption spectrometry. Progesterone was determined by specific radioimmunoassay in homogenized and lyophilized tissue samples after steroid extraction with ethanol. No effect of sample location was found. In placentas of smoking women an increase in cadmium, reduced progesterone and a decrease in iron concentrations were found. Placental copper and zinc concentrations were not altered. In conclusion, the results present new evidence that maternal smoking reduces placental progesterone content and support the established association of smoking with placental cadmium.

Maternal cigarette smoking and oxygen diffusion across the placenta

The aim of this study was to test whether or not adaptations in partial, total and specific oxygen diffusive conductances occur in the placentae of women who smoke cigarettes during pregnancy and help to compensate for intrauterine fetal hypoxic stress. Tissue sections were randomly sampled from human term placentae divided into two groups (non-smokers and smokers) according to maternal smoking status. In smokers, status was expressed as either declared smoking rate or level of plasma cotinine (the major metabolite of nicotine). Sections were analysed stereologically to estimate key structural quantities (vascular volumes, exchange surface areas, tissue diffusion distances). These were combined with previously-published physicochemical quantities (oxygen-haemoglobin reaction rates and tissue oxygen diffusion coefficients) in order to estimate the partial conductances of six tissue compartments of the oxygen pathway: maternal erythrocytes and plasma, villous trophoblast, villous stroma (including fetal capillary wall), fetal plasma and erythrocytes. From partial conductances and birthweights, total and specific conductances were calculated for each placenta. Results were assessed statistically by analyses of variance and t -tests. Despite apparent improvements in the partial conductances of the maternal erythrocytes and plasma, total and specific conductances did not alter significantly in smoking groups. However, the relative biases affecting these estimates may be different in smokers and non-smokers. We conclude that total conductance does not increase in placentae associated with maternal smoking. However, given that the fetus suffers chronic hypoxic stress as a consequence of smoking (evidenced here by elevated haematocrits), even a constant diffusive conductance implies a reduced transplacental partial pressure gradient. This could be a contributory factor to the reduced birthweight.

Concordant in situ and in vitro data show that maternal cigarette smoking negatively regulates placental cytotrophoblast passage through the cell cycle

Maternal cigarette smoking is associated with fetal growth restriction and other pregnancy complications. To investigate possible mechanisms involving the placenta, we studied the morphology of first trimester chorionic villi from mothers who smoked. In mothers who smoked > 20 cigarettes/day, floating villi showed focal defects including an absence of cytotrophoblast stem cells and an abnormal thinning of the syncytium. Anchoring villi displayed a striking increase in the number of cytotrophoblast columns that failed to reach the uterus or degenerated in the intervillous space. Many samples showed a significant reduction in the number of anchoring villi. Also, the number of Ki67-positive cytotrophoblasts was dramatically decreased, indicating that fewer cells were in S phase of the mitotic cycle. Together, these results suggested premature depletion of the cytotrophoblast stem cell population. To test this hypothesis, we exposed anchoring villi from nonsmokers to nicotine in vitro and analyzed the effects on cytotrophoblast passage through the cell cycle. Nicotine (0.23 to 6.0 microM) negatively affected the expression of a number of cell cycle regulators/markers and BrdU incorporation, without discernable effects on apoptosis. These results link abnormal placental development secondary to maternal cigarette smoking to a substantial decrease in the mitotic potential of cytotrophoblasts.

A quantitative study on the effects of maternal smoking on placental morphology and cadmium concentration

The aim of this study was to quantify the effects of maternal cigarette smoking on placental morphology, paying particular attention to variables known to be influential in facilitating oxygen diffusion. Structural quantities were estimated by stereological analyses of placental samples drawn from non-smoking and smoking women whose smoking habits were assessed both subjectively (from volunteered cigarette consumption) and objectively (by determining levels of plasma cotinine, a major metabolite of nicotine). Concentrations of placental cadmium were also measured. In the smoking group, maternal and fetal haematocrits were elevated and mean birthweight was reduced. Within placentae, the most significant alterations were increases in cadmium levels, the relative volumes of maternal intervillous space, the relative surface areas of fetal capillaries and decreases in the relative and absolute volumes of fetal capillaries. Findings indicate that changes in capillary volume are the result of a decrease in mean capillary diameter rather than total length. The mean thickness of the trophoblast component of the villous membrane was also increased in the smoking group. Although increased haematocrits suggest that fetuses of smoking mothers suffer hypoxic stress, these morphological changes are likely to compromise, rather than assist, transplacental oxygen transfer. This is in marked contrast to the adaptive changes seen in pregnancies associated with preplacental hypoxia and suggests that other factors might be compromising the fetoplacental unit. Finally, although the morphological changes associated with maternal smoking seem to be the result of an all-or-none, rather than dose-dependent, effect, the available evidence is not conclusive.