Smoking enhances oxytocin-induced rhythmic myometrial contraction

Changes in the conflicting nongenomic effects of progesterone in rat myometrium during pregnancy

AIMS

Although the functions of progesterone in the myometrium are well-established, the nongenomic effects of progesterone in pregnant myometrial contractions are still unclear. Therefore, this study aimed to investigate changes in the nongenomic effects of progesterone during pregnancy.

MAIN METHODS

Myometrial strips were obtained from non-pregnant, pregnant, and postpartum rats, and the nongenomic effects of progesterone in the myometrium during pregnancy were examined. Additionally, the influence of actinomycin D and cycloheximide and the effects of Org OD-02-0 (a specific membrane progesterone receptor (mPR) agonist) in the myometrium were investigated. Moreover, DNA microarray and quantitative real-time polymerase chain reaction (qRT-PCR) were performed to identify genes involved in progesterone-induced effects in the myometrium.

KEY FINDINGS

Progesterone did not cause rhythmic contractions in non-pregnant myometrium but induced rhythmic contractions in pregnant myometrium, with the effects peaking at 20 d + 8 h of pregnancy. However, myometrial contractions decreased after delivery and were restored to non-pregnant levels at 7 d postpartum. Additionally, progesterone stably inhibited high KCl-induced myometrial contractions during pregnancy. Moreover, the nongenomic effects of progesterone were unaffected by actinomycin D or cycloheximide, and Org OD-02-0 effectively mimicked these effects. DNA microarray analysis and qRT-PCR revealed a significant increase in mPRβ gene expression during pregnancy. However, mPRα, mPRγ, mPRδ, and mPRε expression levels remained unchanged.

SIGNIFICANCE

The stimulatory nongenomic effect of progesterone, which was inducible and mPRβ-dependent during pregnancy, may be involved in parturition. The inhibitory effect, which was constitutive and depended on other mPRs, may be involved in pregnancy maintenance.

The long-term effects of heated tobacco product exposure on the central nervous system in a mouse model of prodromal Alzheimer's disease

Heated tobacco products (HTPs) have emerged as novel alternatives to conventional cigarettes (CCs), marketed by the tobacco industry as having a reduced potential for harm. Nevertheless, a significant dearth of information remains regarding the long-term effects of HTPs on the central nervous system (CNS). Here, we sought to shed light on the repercussions of prolonged exposure to HTPs on the CNS, employing a mouse model mimicking prodromal Alzheimer's disease (AD). Our study entailed subjecting App knock-in mice to 16 weeks of HTP exposure, administered 5 days per week, with serum cotinine concentration serving as confirmation of HTP exposure within this model. Histological analysis, aimed at assessing amyloid pathology, unveiled a minimal impact attributable to HTPs. However, exploration of differentially expressed genes in the cerebral cortex, using unadjusted p values, indicated an association between HTP exposure and non-inflammatory pathways, specifically linked to neurohypophyseal and neuropeptide hormone activity within the CNS. Of note, similar results have already been observed after exposure to CCs in vivo. Our study not only contributes insights into the potential non-inflammatory effects of HTPs within the context of AD pathogenesis but also underscores the significance of continued research to comprehend the full scope of their impact on the CNS.

Conflicting Nongenomic Effects of Progesterone in the Myometrium of Pregnant Rats

Recently, it has been suggested that progesterone affects the contractile activity of pregnant myometrium via nongenomic pathways; therefore, we aimed to clarify whether progesterone causes and/or inhibits pregnant myometrial contractions via nongenomic pathways. Our in vitro experiments using myometrial strips obtained from rats at 20 days of gestation revealed that progesterone caused myometrial contractions in a concentration- and time-dependent manner at concentrations up to 5 × 10-7 M; however, this effect decreased at concentrations higher than 5 × 10-5 M. Similarly, progesterone enhanced oxytocin-induced contractions up to 5 × 10-7 M and inhibited contractions at concentrations higher than 5 × 10-5 M. Conversely, progesterone did not enhance high-KCl-induced contractions but inhibited contractions in a concentration- and time-dependent manner at concentrations higher than 5 × 10-7 M. We also found that RU486 did not affect progesterone-induced contractions or the progesterone-induced inhibition of high-KCl-induced contractions; however, progesterone-induced contractions were blocked by calcium-free phosphate saline solution, verapamil, and nifedipine. In addition, FPL64176, an activator of L-type voltage-dependent calcium channels, enhanced high-KCl-induced contractions and rescued the decrease in high-KCl-induced contractions caused by progesterone. Together, these results suggest that progesterone exerts conflicting nongenomic effects on the contractions of pregnant myometrium via putative L-type voltage-dependent calcium channels.

Maternal cigarette smoking before and during pregnancy and the risk of preterm birth: A dose-response analysis of 25 million mother-infant pairs

BACKGROUND

Most of the women who smoke before pregnancy continue smoking during pregnancy, and some start to quit smoking after being pregnant, although existing guidelines for pregnancy recommend that women who smoke should quit smoking before pregnancy. Findings about the timing and intensity of maternal smoking, especially low-intensity smoking (1-9 cigarettes per day), and preterm birth are still inconsistent and ambiguous. This study aimed to examine the association of the timing of smoking and doses of smoking before pregnancy and during the first or second trimester of pregnancy with preterm birth in a large-scale population-based retrospective cohort study.

METHODS AND FINDINGS

We used nationwide birth certificate data from singleton mother-infant pairs in the United States National Vital Statistics System, 2011-2018. All adult women with live singleton births, without preexisting hypertension or diabetes, and with complete data on smoking and gestational age at delivery were included. Participants reported their smoking status (yes or no) and daily number of cigarettes consumed before and during each trimester of pregnancy. The outcome of interest was preterm birth, defined as a birth before 37 weeks of gestation. Logistic regression models were used to estimate the odds ratio (OR) with 95% confidence intervals (CIs) of preterm birth associated with smoking status and the number of cigarettes consumed, adjusting for maternal age, race/ethnicity, parity, education levels, prepregnancy BMI, previous history of preterm birth, marital status, infant sex, and initiation of prenatal care. This study included 25,623,479 women, with a mean age of 29 years (range 20-50 years); 13,742,486 (53.6%) participants were of non-Hispanic white ancestry, 5,971,598 (23.3%) of Hispanic ancestry, and 3,417,456 (13.34%) of non-Hispanic black ancestry. The prevalence of preterm birth was 9.3% (n = 2,378,398). We found that maternal smoking during pregnancy, even at a very low level of intensity, was associated with an increased risk of preterm delivery. The adjusted ORs (95% CI) of preterm birth for mothers who smoked 1-2, 3-5, 6-9, 10-19, and ≥20 cigarettes per day during the first trimester compared with mothers who did not smoke were 1.31 (1.29-1.33), 1.31 (1.30-1.32), 1.33 (1.31-1.35), 1.44 (1.43-1.45), and 1.53 (1.52-1.55), respectively (all P values < 0.001), whereas for those who smoked during the second trimester, the corresponding ORs were 1.37 (1.35-1.39), 1.36 (1.35-1.38), 1.36 (1.34-1.38), 1.48 (1.47-1.49), and 1.59 (1.58-1.61), respectively (all P values < 0.001). Furthermore, smokers who quit before pregnancy, regardless of smoking intensity, had a comparable risk of preterm birth with nonsmokers, although this was not the case when cessation occurred in the first or second trimester of pregnancy. The major limitation of this study is the self-reported information about smoking, which may be subject to information bias. In addition, we cannot rule out the possibility of residual confounding caused by unmeasured factors in an observational research design.

CONCLUSIONS

In this study, we observed that low-intensity cigarette consumption during either the first or second trimester of pregnancy, even as low as 1-2 cigarettes per day, was associated with an increased risk of preterm birth. These findings suggest that there is no safe level or safe trimester for maternal smoking during pregnancy. Women of reproductive age who smoke should be strongly encouraged and supported to quit smoking before pregnancy.

The relationship between gestational active and passive smoking and early postpartum complications

Objective: The studies especially on the postpartum effects of passive exposure to cigarette smoke are limited, although there are studies investigating early and late postpartum effects of active smoking during pregnancy. This study aimed to investigate the relationship between gestational active and passive smoking and early postpartum complications.Methods: This study was conducted with 217 women in the early postpartum period (first 7 days after birth) in a research hospital, gynecology and obstetrics clinic. Data were collected using the questionnaire form prepared in accordance with the literature by the face-to-face interview method. They were evaluated in the SPSS 23.0 program, and descriptive statistics, logistic regression analysis in multivariate analyses and multiple linear regression analysis were in the analysis of data.Results: In the study, it was found that active smoking was associated with cardiac anomalies (OR = 0.18, 95% = CI 0.03-0.91; p = .039), developmental retardation (OR = 0.11, 95% CI = 0.02-0.56; p = .008), respiratory distress (OR = 0.12, 95% CI = 0.02-0.58; p = .008), low birth weight (OR = 0.22, 95% CI = 0.08-0.57; p = .003) and premature labor (OR = 0.30, 95% CI = 0.16-0.59; p = .000) while passive smoking was associated with premature labor (OR = 0.47, 95% CI = 0.25-0.89; p = .021). It was determined that passive smoking was associated with gestational hypertension (OR 0.30, 95% CI = 0.09-0.85; p = .025). Nevertheless, it was found that active smoking negatively affected the infant's birth weight (p = .000), length (p = .040), head circumference (p = .000) and breastfeeding (p = .005).Conclusion: Gestational active and passive smoking has significant negative effects on maternal and infant health in the early postpartum period.

Smoking alters hydroxyprostaglandin dehydrogenase expression in fetal membranes

INTRODUCTION

The way in which tobacco smoking increases the risk of preterm labor remains uncertain. Altered prostaglandin metabolism is one potential mechanism.

METHODS

Proteins in fetal membrane samples (amniochoriodecidua) from 20 women were relatively quantified using Tandem Mass Tagging nano-liquid chromatography mass spectrometry.

RESULTS

Prostaglandin synthases and two enzymes involved in prostaglandin degradation, hydroxyprostaglandin dehydrogenase (HPGD) and CBR1, were detected by the mass spectrometer. The expression of HPGD was significantly lower in smokers relative to non-smokers (0.43 fold, p = 0.016). There was no effect of labor, inflammatory status or gestational age on the HPGD levels.

DISCUSSION

We describe for the first time an association between maternal smoking and HPGD expression. We propose that reduced expression of HPGD is one mechanism through which smoking may contribute to preterm labor. Lower levels of this enzyme, key to metabolising prostaglandins, may result in higher levels of prostaglandins and therefore precipitate labor prematurely.

The steroid hormone dydrogesterone inhibits myometrial contraction independently of the progesterone/progesterone receptor pathway

AIMS

In this study, we aimed to investigate the direct effects of steroid hormones on pregnant myometrial contraction.

MAIN METHODS

The effect of steroids on oxytocin-induced contraction was examined in vitro using pregnant rat or human myometrium. Subsequently, we evaluated whether RU486, a potent progesterone antagonist, influenced the effects of progestin on myometrial contraction. Additionally, we evaluated the effects of progestin on high-concentration KCl-induced contraction caused by voltage-dependent calcium channels in order to investigate the mechanisms involved in this process.

KEY FINDINGS

Of the natural steroids examined, 17β-estradiol, progesterone, testosterone, cortisol, and aldosterone did not influence oxytocin-induced contraction at concentrations <10^-6 M. Of the tested progestins, medroxyprogesterone acetate, norethisterone, chlormadinone acetate, levonorgesterol, 17α-hydroxyprogesterone capronate, and dienogest had no effect on contraction at <10^-6 M. However, dydrogesterone showed rapid and direct inhibition of contraction at 10^-6 M, and this inhibitory effect was dependent on dose and time. RU486 did not block the inhibitory effects of dydrogesterone on contraction. High-concentration KCl-induced contraction was also inhibited by dydrogesterone, and the inhibitory effects of dydrogesterone were observed at concentrations as low as 10^-7 M. Additionally, oxytocin-induced contraction in pregnant human myometrium was inhibited by 10^-6 M dydrogesterone.

SIGNIFICANCE

These results suggested that the rapid and direct effects of dydrogesterone on myometrial contraction were caused by a nongenomic pathway and that the progesterone receptor was not required for dydrogesterone action. Additionally, the mechanism of dydrogesterone action may involve voltage-dependent calcium channels.

Dose-Dependent Differential Effects of In Vivo Exposure of Cadmium on Myometrial Activity in Rats: Involvement of VDCC and Ca2+-Mimicking Pathways

Present study was undertaken to study the effect of 28-days exposure of female adult rats to cadmium (Cd) in drinking water @ 3, 10 and 30 parts per million (ppm) on myometrial responsiveness to different spasmogens and unravel the possible mechanism of alterations in myometrial activity. Cadmium and Ca²⁺ levels in blood and uterus were measured by atomic absorption spectroscopy while isometric tension in myometrial strips was measured using data acquisition system-based physiograph. Dose-dependent increase in levels of cadmium was observed in both blood and uterus while calcium was increased only in the uterus as compared to those in control. Significant increase in absolute tension and mean integral tension along with non-significant increase in frequency of myometrial contraction was observed in rats of Cd-treated groups. As compared to the control, cadmium decreased and increased the effects of calcium chloride, 80 mM KCl, histamine (0.1 μM) and oxytocin (10^-2 IU/ml) in lower-dose (3 ppm) and higher-dose groups (10 and 30 ppm), respectively. Cadmium potentiated and inhibited the relaxant response to phenylephrine in myometrium of rats at lower-dose (3 ppm) and highest-dose (30 ppm) Cd-treated groups, respectively. Results of our study revealed that Cd accumulates in the myometrium of rats and alters its responsiveness to oxytocin, histamine, 80 mM KCl, calcium chloride and phenylephrine, and these effects are differentially mediated depending on levels of exposure possibly through voltage-dependent calcium channel (VDCC) and Ca²⁺-mimicking pathways.

Oxytocin is lower in African American men with diabetes and associates with psycho-social and metabolic health factors

Objective

Recently, it has been suggested that oxytocin (OT) has a role in metabolism and neuropsychiatry health and disease, and therefore, it may represent a potential therapeutic target. The current study aimed to investigate relationships between OT and glycemic status along with psycho-social and behavioral factors.

Design and methods

A total of 92 obese or overweight, African American, male subjects were enrolled in the study. Biometric and biochemical data were collected including oral glucose tolerance testing and urinary OT (measured by ELISA). Subjects also completed questionnaires on social and lifestyle factors.

Results

OT levels were found to be significantly lower in subjects with type 2 diabetes mellitus (T2DM) compared to normal glucose tolerance (p<0.05). When stratified by OT tertiles, subjects with higher OT had lower weight, body mass index (BMI) and hemoglobin A1c, but higher eGFR which remained significant after BMI adjustment. The highest OT tertile also had more smokers and more users of psychiatric medications. A stepwise ordered logistic regression supported these findings and could account for 21% of the variation in OT categories (pseudoR² = 0.21).

Conclusions

In this unique population, OT was found lower in subjects with diabetes but higher with better renal function, cigarette smoking and use of psychiatric medications. Future studies are needed to confirm these findings and examine the potential therapeutic role of OT.

Functional involvement of L-type calcium channels and cyclic nucleotide-dependent pathways in cadmium-induced myometrial relaxation in rats

Modulation of myometrial spontaneity by cadmium (Cd) and its regulatory pathways was studied in rat uterus in the absence and presence of blockers of different signaling pathways. Isometric tension in myometrial strips, under a resting tension of 1 g, mounted in organ bath containing Ringer-Locke solution (RLS) continuously aerated with carbogen, was measured using data acquisition system-based physiograph and Lab Chart Pro V7.3.7 software. Mean integral tension was measured for 8 min. Cd (1 nM-0.1 mM) not only produced concentration-dependent inhibitory effect on rat myometrium but it (10 µM) also significantly ( p < 0.05) inhibited calcium chloride and BAY K-8644-induced myometrial contraction. Glybenclamide (10 µM), 4-aminopyridine (1 mM), and propranolol (10 µM) failed to significantly attenuate Cd-induced inhibitory responses, while L-NAME (0.1 mM), 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 25 µM), and 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ 22536; 1 µM) significantly ( p < 0.05) produced inhibitory effects on Cd-induced myometrial relaxation. Phenylephrine (1 nM-10 µM) and salbutamol (0.01 nM-0.1 µM)-induced relaxant effects on rat myometrium were significantly potentiated by 10 µM Cd. Thus based on the results of present functional study, it may be inferred that inhibitory effects of Cd on rat myometrium are mediated through blockade of L-type calcium channels and activation of NOS-NO-sGC and/or AC-cAMP pathways.

Smoking and Preterm Birth

Premature birth is a significant global problem and the leading cause of newborn deaths. Tobacco smoking has been associated with premature birth for over 50 years. The mechanisms through which smoking exerts its effects on pregnancy outcomes remain unclear. In this review, we discuss rates of prematurity and smoking in pregnancy, the evidence of a causal relationship between tobacco and preterm birth, and proposed biochemical pathways through which the interaction is mediated. The suggested mechanisms include nicotine-induced vasoconstriction, carbon monoxide-induced fetal hypoxia, cadmium disruption of calcium signaling, altered steroid hormone production, disruption of prostaglandin synthesis, and changed responses to oxytocin. The relative importance of each of these pathways is yet to be ascertained. Further research is necessary to explore the mechanisms through which smoking exerts its effect on gestational length and the process of parturition. Moreover, the risks of nicotine replacement in pregnancy should be investigated further.

Effects of ovarian hormone treatment on the gene expression of muscarinic acetylcholine receptors in the ovariectomized rat myometrium

We investigate the effects of ovarian hormone on the gene expression of muscarinic acetylcholine receptors (M1-M5) in the myometrium using real-time PCR and evaluate the relationships between their expression and that of ovarian hormone receptors (ERα, ERβ, and PgR). Wistar rats were sham operated (SO) or ovariectomized (OVX) and treated with vehicle, estradiol (E2), progesterone (P4), or both E2 and P4 for 2 days beginning on postoperative day 33. M1 and M4 mRNA expressions were not detected in the myometrium. M2 mRNA expression did not change significantly in the OVX and OVX+P4 groups compared to the SO group, but increased significantly in the OVX+E2 group and was normalized in the OVX+E2P4 group. M3 mRNA expression increased significantly in the OVX and OVX+P4 groups compared to the SO group, but was normalized in the OVX+E2 and OVX+E2P4 groups. M5 mRNA expression did not change significantly in all experimental groups. ERα mRNA expression increased significantly in the OVX, OVX+E2, and OVX+P4 groups compared to the SO group, but was normalized in the OVX+E2P4 group. The changes in ERβ mRNA expression were similar to those of M3 mRNA expression in all experimental groups. In contrast, the changes in PgR mRNA expression did not correspond with that of M2, M3, or M5 mRNA expression in any of the experimental groups. Additionally, we evaluated the relationship between the expression of muscarinic acetylcholine receptors and ovarian hormone receptors in estrus cycle. M2 mRNA expression increased significantly in diestus and metaestrus compared in proestrus and estrus. M3 mRNA expression increased significantly in only diestrus compared in the other stages. In contrast, M5 mRNA expression did not change in estrus cycle. The changes in ERα mRNA expression appeared to be similar to those of M2 in estrus cycle, but no significant difference was found. The changes in ERβ mRNA expression were similar to those of M3 mRNA expression. The change in PgR mRNA expression increased significantly in diestrus compared in metaestrus, but did not correspond with that of M2, M3, or M5 mRNA expression in estrus cycle. When acetylcholine sensitivity in the myometrium was compared between diestrus and estrus, the sensitivity is significantly lower in estrus than in diestrus. These results suggest that ovarian hormones influence the expression of M2 and M3 in the myometrium by regulating the expression of hormone receptors. E2 may upregulate M2 via ERα, but P4 may downregulate M2 by inhibiting ERα via PgR. E2 may downregulate M3 by inhibiting ERβ, but P4 may not regulate the expression of M3 and ERβ. M5 may be a constitutive muscarinic receptor in the myometrium because neither E2 nor P4 influence the expression of M5. The combination of E2 and P4 may contribute the reproduction by quieting down the acetylcholine-induced myometrial contraction.

Effects of cigarette smoking on reproduction

BACKGROUND Cigarette smoking is associated with lower fecundity rates, adverse reproductive outcomes and a higher risk of IVF failures. Over the last few decades, prevalence of smoking among women of reproductive age has increased. This review focuses on current knowledge of the potential effects of smoke toxicants on all reproductive stages and the consequences of smoke exposure on reproductive functions. METHODS We conducted a systematic review of the scientific literature on the impact of cigarette smoking and smoke constituents on the different stages of reproductive function, including epidemiological, clinical and experimental studies. We attempted to create hypotheses and find explanations for the deleterious effects of cigarette smoke observed in experimental studies. RESULTS Cigarette smoke contains several thousand components (e.g. nicotine, polycyclic aromatic hydrocarbons and cadmium) with diverse effects. Each stage of reproductive function, folliculogenesis, steroidogenesis, embryo transport, endometrial receptivity, endometrial angiogenesis, uterine blood flow and uterine myometrium is a target for cigarette smoke components. The effects of cigarette smoke are dose-dependent and are influenced by the presence of other toxic substances and hormonal status. Individual sensitivity, dose, time and type of exposure also play a role in the impact of smoke constituents on human fertility. CONCLUSIONS All stages of reproductive functions are targets of cigarette smoke toxicants. Further studies are necessary to better understand the deleterious effects of cigarette smoke compounds on the reproductive system in order to improve health care, help to reduce cigarette smoking and provide a better knowledge of the molecular mechanisms involved in reproductive toxicology.

Cigarette smoke extract enhances oxytocin-induced rhythmic contractions of rat and human preterm myometrium

Although smoking during pregnancy is a major risk factor for preterm delivery, the underlying mechanism by which smoking stimulates uterine contractions is still poorly understood. In the present study, we tried to clarify the effects of smoking on myometrial contractility induced by oxytocin (OT) using cigarette smoke extract (CSE). Myometrial strips, which were taken from the rat on day 16 of pregnancy, and from human preterm and term delivery groups, were incubated overnight with several doses of CSE at 37 degrees C under non-hormonal conditions. The uterine contractile sensitivity and activity (force and frequency) upon exposure to OT were investigated. Furthermore, the expression levels of oxytocin receptor (OTR) mRNA in the myometrial strips were investigated by real-time PCR. Contractile sensitivity to OT in the rat CSE (10(-7) pieces/ml) group was found to be significantly higher than in the control group (P < 0.05). Contractile activity did not differ between the CSE and control groups. The expression levels of rat OTR mRNA in the CSE (10(-7) pieces/ml) group were significantly higher than in the control group (P < 0.01). Similarly, in preterm myometrial strips, the expression levels of human OTR mRNA in the CSE (10(-7) pieces/ml) group were significantly higher than in the control group (P < 0.05). These findings suggest that CSE directly increases the contractile sensitivity of preterm myometrium in response to OT by upregulating the expression of OTR mRNA and thereby increases the risk of preterm delivery in women, who smoke during pregnancy.

Hormonal changes accompanying cigarette smoke-induced preterm births in a mouse model

Epidemiologic evidence indicates that maternal smoking increases the risk of preterm birth. While a number of plausible mechanisms for early delivery have been offered, the role of gestational hormones in this smoke-induced outcome is uncertain. Thus, a toxicologic study was performed to examine the effects and underlying hormonal mechanisms of mainstream cigarette smoke (MCS) exposure on gestational duration. Pregnant B6C3F1 mice were exposed by inhalation to MCS for 5 days/week (4 hrs/day) from Gestational Day (GD) 4 to parturition. Smoke-induced effects on gestational length, interpubic ligament length, maternal hormone secretion patterns (estradiol-17beta, progesterone, prolactin, and relaxin), body weight gain, postimplantation loss, litter size, and offspring sex ratio were examined. Dams exposed to MCS at a concentration equivalent to smoking less than one pack of cigarettes/day (carbon monoxide = 25 parts per million, total suspended particulates = 16 mg/m3) demonstrated a significant (P < 0.05) shortening of gestational duration (compared with pregnant, air-exposed mice). In addition, MCS-exposed mice sacrificed on GD 18 had significantly (P < 0.05) increased interpubic ligament length, elevated serum estrogen levels, and a reduced progesterone to estradiol-17beta ratio (compared with air-exposed controls); levels of progesterone and prolactin were only modestly decreased and increased, respectively, in the MCS-exposed mice. Smoke exposure had no significant effects on maternal relaxin levels, body weight gain, postimplantation loss, litter size, or sex ratio. Results of this study demonstrate that inhalation exposure of pregnant mice to a low dose of MCS shortens gestation and alters hormone secretory patterns, which are important for maintaining pregnancy and inducing parturition. These findings support the view that pregnant women who smoke (even modestly) may be at increased risk for preterm birth, and that early delivery may be related (at least partly) to MCS-induced.

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.