2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) alters intrathymic T-cell development in mice

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) was administered to 2-4-week-old mice (5, 25, and 50 micrograms/kg body wt.) and to in vitro cultures (10(-9) M) of fetal thymi. By monitoring thymocyte populations with respect to the differentiation antigens CD4 and CD8, it was found that the cell number in all thymocyte populations except for CD8+ decreased significantly compared with controls. In vivo the most marked decrease occurred among double negative (DN) and double positive (DP) cells, whereas in vitro, the DP cells were most severely affected. The cell number had already decreased to some extent by day 1 after a dose of 50 micrograms/kg body wt. of TCDD, although a severe reduction did not become apparent until day 4. There was a clear dose/response relationship between 5 and 50 micrograms/kg body wt. Autoradiography and liquid scintillation counting studies showed that incorporation of [3H]thymidine in the thymus had already decreased 24 h after TCDD treatment, with the decrease being even more pronounced at 48 h. By 96 h, the rate of cell proliferation had returned to approximately normal values. The results show that TCDD has a long-lasting effect on thymocyte abundance together with a transient effect on cell proliferation. This indicates that in addition to the initial effects of TCDD on cell proliferation, it may also more permanently disturb the normal process of elimination by means of selection.     

Perinatal thymocyte antigen expression and postnatal immune development altered by gestational exposure to tetrachlorodibenzo-p-dioxin (TCDD).

In utero exposure to the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was found to alter expression of murine thymocyte fetal cell-surface markers. Pregnant mice were treated (via gavage) with 0, 1.5, or 3.0 micrograms TCDD/kg/day in corn oil on gestational days (gd) 6-14. Offspring were examined on gd 18 and postnatally on d6, d14, and d21, and at 7, 8, and 10 weeks of age. Severe thymic atrophy and cellular depletion were found both pre- and postnatally in TCDD-exposed mice. Immunocytochemical localization of the Thy 1.2 antigen on gd 18 thymocytes revealed no TCDD-related changes in cellular distribution. Flow cytometric analysis, however, indicated that the TCDD treatment resulted in a significant decrease in the percentage of CD4+8+ fetal thymocytes, as well as significantly increased CD4-8- and CD4-8+ thymocytes. The increased CD4-8+ population after TCDD was not from induction of Ts cells. At 7-8 weeks postnatally, no differences existed between control and treatment groups in mitogen responses and antibody plaque response. However, altered thymocyte antigen expression was found to correlate with altered postnatal immune function, as evidenced by decreased cytotoxic T lymphocyte response at 8 weeks of age. Taken together, these results indicate that immunosuppression following prenatal exposure to TCDD can be readily detected by qualitative and quantitative changes in the cell surface phenotype of fetal thymocytes. Furthermore, the observed altered distribution suggests that TCDD inhibits normal thymocyte maturational processes.     

Impairment of prothymocyte activity by 2,3,7,8-tetrachlorodibenzo-p-dioxin

Exposure of experimental animals to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) results in severe thymic atrophy and suppression of cell-mediated and humoral immune functions. However, despite much effort the mechanism by which TCDD produces these responses, particularly thymic atrophy, remains unclear. In this report, we have examined the effect of acute TCDD exposure on lymphocyte stem cells in young adult BALB/c mice to determine whether alterations to events early in T lymphopoiesis contribute to TCDD-induced thymic atrophy. TCDD produced a dose-dependent reduction in thymic weight and cellularity following a single dose of 5 to 120 micrograms TCDD/kg. This thymic atrophy correlated with a dose-dependent suppression of the biosynthesis and mRNA levels of the lymphocyte stem cell-specific DNA polymerase terminal deoxynucleotidyl transferase in bone marrow and thymus. However, the reduction in thymic terminal deoxynucleotidyl nucleotidyl transferase synthesis, on a per cell basis, was less than that observed in bone marrow. Intrathymic CD4/CD8 and IL-2R expression demonstrated only mild alterations after exposure to 30 micrograms TCDD/kg. These data suggest that thymocytes are more refractory to TCDD than are pre-T cells. To assess this possibility directly, bone marrow prothymocytes from TCDD-treated donor mice were examined for their capacity to reconstitute the thymuses of adoptive, irradiated recipients. Our results indicate that prothymocyte activity was severely impaired by TCDD exposure and that this effect occurred at low tissue levels of TCDD. In contrast, we observed no reduction in the number of colony-forming unit-granulocyte macrophage and a moderate decrease in colony-forming unit-spleen. These data suggest that TCDD-induced thymic atrophy is the result, at least in part, of impaired thymic seeding by prothymocytes.     

Effects of TCDD on embryonic ureteric epithelial EGF receptor expression and cell proliferation

The potent toxin 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is teratogenic in mice, producing hydronephrosis and cleft palate. Because of the long half-life of TCDD, the urinary tract is exposed throughout development after a single dose on gestation day (GD) 10 or earlier. TCDD-induced hydronephrosis is a consequence of occlusion of the ureter by epithelial cells. Since embryonic growth factors and the epidermal growth factor (EGF) receptor are probably involved in regulation of embryonic cell proliferation, this study examines the effects of TCDD on expression of EGF receptors and proliferation of ureteric epithelial cells in vivo and in culture. After exposure to TCDD by gavage (12, 24, or 30 micrograms/kg on GD 10; 6 or 24 micrograms/kg on GD 12) the mean cell depth of the ureteric and bladder epithelia was increased. EGF receptors were detected immunohistochemically in sectioned urinary tracts. The expression of receptors decreased with advancing development in control ureteric epithelia. However, after TCDD exposure the level of EGF receptors failed to decline. The incorporation of 3H-TdR was observed in sections by autoradiography, and after exposure to TCDD more epithelial cells showed incorporation than was apparent in controls. Transmission electron microscopy (TEM) of embryonic ureters from fetuses exposed to TCDD in vivo showed no cytotoxicity in basal cells and the cells remained undifferentiated, as in controls. Ureters taken from GD 12 embryos and cultured with 1 x 10(-10)M TCDD showed ureteric epithelial hyperplasia without cytotoxicity, but at 1 x 10(-8)M TCDD evidence of cytotoxicity was observed by TEM. The levels of TCDD found in fetuses after in vivo exposure (204-307 pg/fetus, with 1-2 pg in the urinary tract) compare well with the in vitro level (32 pg/ml), which was most effective in producing hyperplasia of the epithelial cells. The present study correlates a TCDD-induced increase in cell depth with altered regulation of EGF receptors and excessive proliferation, both in vivo and in cultured embryonic ureters.     

Accumulation of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in porcine preovulatory follicles after in vitro exposure to TCDD: effects on steroid secretion and cell proliferation

The present experiments were conducted to test 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) accumulation in the tissues, and its influence on cell proliferation and steroid secretion. A dose of 3.2 ng of TCDD/g tissue was added at the beginning of the culture, and the media were changed every 24 h or not changed till the end (96 h) of the culture. TCDD in the tissue was analysed by mass spectrometry, and the percentage of proliferating cells was measured using the MIB-1 labelling index. TCDD added to the culture medium accumulated in the tissues after 24 h (59.3%) and 96 h (81.2%) of exposure. The accumulative effect of TCDD was manifested by a reduction in the percentage of proliferating cells (53.5 and 33.8%, after 24 and 96 h exposure, respectively). A single exposure to TCDD had no effect on progesterone, reduced testosterone secretion and caused a significant increase in oestradiol secretion. Prolonged exposure to TCDD caused an increase in the concentration of the three steroids investigated in the culture medium. The results suggest that TCDD action is complex in the follicles.     

Preferential proliferation of T cell receptor V gamma 3-positive cells in IL-2-stimulated fetal thymocytes

Thymocyte cell suspensions, prepared from mice at different ages, were cultured in vitro with human rIL-2. This stimulation resulted in a cell population that contained almost 50% TCR-gamma delta-positive cells if thymocytes were taken from fetal day 17 until just after birth. Analysis of the variable (V gamma) region used by the TCR-gamma delta cells revealed that 90% of them expressed TCR-V gamma 3, and less than 5% expressed TCR-V gamma 2. Cells positive for TCR-alpha beta were barely detectable. If fetal day 18 organ cultured thymus lobes, instead of a cell suspension, were stimulated with IL-2, no rise in the number of TCR-V gamma 3+ or TCR-delta+ cells was observed, whereas a partial outgrowth of TCR-alpha beta+ cells occurred. From day 1 after birth, the number of TCR-gamma delta cells recovered from an IL-2-stimulated thymocyte cell suspension dropped to reach a plateau of 15% of the total cell number, whereas TCR-V gamma 3+ cells became undetectable in older animals. TCR-alpha beta+ cells, on the other hand, quickly rose in cell number after birth. Kinetic analysis showed that the preferential outgrowth of TCR-V gamma 3+ cells in IL-2-stimulated fetal day 18 thymocyte cell suspensions was present from the onset of the culture; a significant proliferation of CD4 or CD8 single positive TCR-alpha beta cells was never observed. This lack of proliferation of TCR-alpha beta cells was not due to inhibition by the activated TCR-V gamma 3+ cells. Throughout the IL-2 culture, one-fourth of the TCR-V gamma 3+ thymocytes was positive for CD8. Analysis of the DNA content and the IL-2 receptor (IL-2R) p55 expression showed that during the first days of culture the TCR-V gamma 3+ cells had a much higher proliferation rate than the TCR-V gamma 3- cells, although TCR-V gamma 3+ IL2R p55+ cells could not be detected. From day 3 to 4 of culture, the proliferation rate of TCR-V gamma 3+ cells equaled that of the rest of the cells and less than 20% of the TCR-V gamma 3+ cells expressed the IL-2R p55. The biologic significance of our findings is discussed.     

Protection by dexamethasone from a lethal infection with Listeria monocytogenes in mice

Abstract The effects of dexamethasone (DEX) on a lethal infection with Listeria monocytogenes were studied in mice. Mice were completely protected against the lethal infection when treated with 3.3 mg per kg of DEX. The effect was observed only when DEX was injected before infection. The control mice died from day 3 to day 5 of infection, whereas DEX-treated mice could eliminate L. monocytogenes cells from the organs by day 11 of infection. High titres of endogenous tumour necrosis factor (TNF), interleukin-6 (IL-6) and gamma interferon (IFN-γ) were induced in the bloodstreams and organs of the drug-free mice. DEX suppressed IL-6 production, but augmented TNF and IFN-γ production within 24 h of infection, whereas production of all three endogenous cytokines was suppressed in the DEX-treated mice on day 3 of infection when the control mice began to die. These results suggest that DEX shows a protective effect on a lethal infection with L. monocytogenes in mice and that regulation of production of endogenous cytokines might be involved in the effect of DEX.     

Modulation of 2,3,7,8-tetrachlorodibenzo-p-dioxin toxicity in F344 rats by di(2-ethylhexyl)phthalate

The effects of cotreatment with a hyperlipidemic chemical, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and a hypolipidemic agent, di(2-ethylhexyl)-phthalate (DEHP), on lipid metabolism and toxicologic responses were studied in F344 rats. Treatment with TCDD alone (160 micrograms/kg) caused an increase in serum triglycerides and cholesterol while treatment with DEHP alone (2 g/kg/day) caused a decrease in triglycerides and cholesterol versus untreated controls. When administered before or after TCDD, DEHP caused a decrease in TCDD-induced hyperlipidemia. This change was attributed to enhanced hepatic peroxisomal beta-oxidation and decreased hepatic lipid synthesis resulting from treatment with DEHP. TCDD treatment produced a fatty liver, as determined by gravimetric analysis of extracted lipid and microscopic examination of liver sections which revealed extensive cytoplasmic vacuolization that stained positive with Oil Red 0, but did not induce peroxisomal beta-oxidation. Thus, an increase in hepatic or serum lipid levels is not sufficient for induction of peroxisome proliferation. Neither TCDD nor DEHP treatment affected mitochondrial beta-oxidation. Pretreatment of rats with DEHP, followed by daily exposure to this hypolipidemic agent after treatment with TCDD, had a partial protective effect against TCDD-induced fatty liver, body weight loss and mortality. Microscopic examination of liver sections confirmed the suppression of TCDD-induced fatty liver by pretreatment with DEHP. When DEHP treatment was initiated after the TCDD dose, there was less protection against the above parameters of TCDD toxicity. This study demonstrates that TCDD-induced fatty liver, hyperlipidemia and mortality can be antagonized by treatment with a hypolipidemic agent such as DEHP.     

Comparisons of the effects of TCDD and hydrocortisone on growth factor expression provide insight into their interaction in the embryonic mouse palate.

Cleft palate (CP) can be induced in embryonic mice by a wide range of compounds, including glucocorticoids and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Hydrocortisone (HC), a glucocorticoid, retards embryonic growth producing small palatal shelves, while TCDD exposure blocks the fusion of normally sized shelves. TCDD induction of CP involves altered differentiation of the medial epithelial cells. Recent studies indicate that growth factors such as EGF, TGF-alpha, TGF-beta 1, and TGF-beta 2 are involved in palatogenesis, regulating proliferation, differentiation, and extracellular matrix production. A synergism has been observed between HC and TCDD in which doses too low to induce CP alone are able to produce greater than 90% incidence when coadministered. In the present study a standard teratology protocol was performed in C57BL/6N mice to examine the synergism at doses lower than those previously published. Data from this study indicate synergistic interactions at doses as low as 3 micrograms TCDD/kg + 1 mg HC/kg. This extreme sensitivity suggests the involvement of a receptor-mediated mechanism possibly resulting in altered regulation of gene expression. Mechanisms of interaction were further studied by comparing growth of the shelves, fate of the medial epithelium, and expression of growth factor mRNAs and peptides. Pregnant mice were dosed on GDs 10-13 with HC (100 mg/kg sc) or with HC (25 mg/kg sc) + TCDD (3 micrograms/kg orally), doses producing 30% and 99% CP, respectively. The interaction between HC and TCDD results in a small HC-like palate, rather than the morphology typical of TCDD-induced clefting. Both compounds inhibited programmed cell death of the medial epithelium, which instead differentiated into an oral-like epithelium. The alterations in growth factor expression after HC or HC + TCDD were similar. Expression of EGF, TGF-beta 1, TGF-beta 2, and EGF receptor increased in specific palatal regions. Increased levels of mRNA were observed only for TGF-beta 1. The effect of TCDD alone on growth factor expression differ from those seen with HC or HC + TCDD. These divergent effects on growth factor expression may contribute to the differences in shelf size and thus to the different mechanisms of HC and TCDD clefting. Thus the synergism between HC and TCDD may involve similar and potentially additive effects on regulators of proliferation and differentiation in the palate, but additional contributing factors cannot be excluded.     

Prenatal Exposure to Dexamethasone in the Mouse Alters Cardiac Growth Patterns and Increases Pulse Pressure in Aged Male Offspring

Exposure to synthetic glucocorticoids during development can result in later cardiovascular and renal disease in sheep and rats. Although prenatal glucocorticoid exposure is associated with impaired renal development, less is known about effects on the developing heart. This study aimed to examine the effects of a short-term exposure to dexamethasone (60 hours from embryonic day 12.5) on the developing mouse heart, and cardiovascular function in adult male offspring. Dexamethasone (DEX) exposed fetuses were growth restricted compared to saline treated controls (SAL) at E14.5, but there was no difference between groups at E17.5. Heart weights of the DEX fetuses also tended to be smaller at E14.5, but not different at E17.5. Cardiac AT_1aR, Bax, and IGF-1 mRNA expression was significantly increased by DEX compared to SAL at E17.5. In 12-month-old offspring DEX exposure caused an increase in basal blood pressure of ∼3 mmHg. In addition, DEX exposed mice had a widened pulse pressure compared to SAL. DEX exposed males at 12 months had an approximate 25% reduction in nephron number compared to SAL, but no difference in cardiomyocyte number. Exposure to DEX in utero appears to adversely impact on nephrogenesis and heart growth but is not associated with a cardiomyocyte deficit in male mice in adulthood, possibly due to compensatory growth of the myocardium following the initial insult. However, the widened pulse pressure may be indicative of altered vascular compliance.     

Tetrachlorodibenzo-p-dioxin exposure alters radial arm maze performance and hippocampal morphology in female AhR mice

Perinatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been reported to alter spatial learning in rats tested on a radial arm maze (RAM). TCDD is believed to exert most of its effects through binding to the aryl hydrocarbon receptor (AhR). To determine whether the AhR mediates TCDD-induced alterations in spatial learning, we tested male and female AhR-knockout (AhR-/-), heterozygous (AhR+/-) and wild-type (AhR+/+) mice on the RAM. AhR+/- male and female mice were time mated, and treated dams were dosed with 5 microg TCDD/kg body weight on day 13 of gestation. When offspring reached adulthood, male and female AhR+/+, AhR+/- and AhR-/- mice from TCDD-exposed and unexposed litters were tested on the eight-arm RAM. After testing, we examined hippocampal morphology as visualized by the Timm's silver sulfide stain. TCDD-exposed female AhR+/- mice made more errors than their respective controls on the RAM and exhibited a decrease in the size of the intra- and infrapyramidal mossy fiber (IIP-MF) field of the hippocampus. None of the other TCDD-exposed groups differed from their respective control groups with regard to maze performance or hippocampal morphology. The reduction of IIP-MF field indicates a possible morphological basis for the learning deficit that was observed in the female AhR+/- mice. It is hypothesized that the effect of TCDD exposure is AhR dependent and that TCDD may alter GABAergic activity in the hippocampus of female mice during development.     

Prenatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin produces alterations in cortical neuron development and a long-term dysfunction of glutamate transmission in rat cerebral cortex

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is considered one of the most toxic dioxin-like compounds. It is ubiquitous in foodstuffs of animal origin and accumulates in the fatty tissues of animals and humans. Prenatal TCDD exposure has been associated, beside other effects, with persistent impaired cognitive development. In the present study, the effects of maternal exposure to TCDD during pregnancy on cortical neuron development at birth and cortical glutamate transmission in new-born, 14- and 60-day-old rat offspring, were investigated. A single dose (0.7μg/kg) of TCDD dissolved in corn oil was orally administrated to the dams on gestational day 18; controls dams were treated with the vehicle. All the experiments have been performed on the male offspring from vehicle-treated (i.e. control group) and TCDD-treated dams. Primary cultures of cerebral cortical neurons obtained from 1-day-old rats born from mothers exposed to TCDD displayed a reduction in cell viability (MTT assay) and an increase in the number of apoptotic nuclei (nuclear staining with Hoechst 33258) possibly associated with altered dendrite outgrowth (MAP2-immunoreactivity) with respect to control cell cultures. These changes were associated with impairment in cortical glutamate transmission, characterized by a reduction in basal and K(+)-evoked outflow as well as a decrease in [(3)H]glutamate uptake. Interestingly, the prenatal TCDD-induced alteration of cortical glutamate signaling is persistent since it was also present in 14- and 60-day-old offspring. Taken together, these results suggest that a single prenatal exposure to TCDD produces alterations in cortical neuron development associated with a long-term dysfunction of glutamate transmission in rat cerebral cortex. The possible relevance of these findings for the understanding of the long-lasting cognitive deficit observed in the offspring from mothers exposed to the toxicant during pregnancy, is discussed.     

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on vitamin A metabolism in mice

This study aimed to clarify the effects of single and repeated administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the activities or expression of some metabolic enzymes of retinoids and the influence of supplemental vitamin A on changed vitamin A homeostasis by TCDD. In Experiment I, the mice were given a single oral dose of 40 mug TCDD/kg body weight, with or without continuous administration of 2,500 IU vitamin A/kg body weight/day, and were killed on day 1, 3, 7, 14, and 28. In Experiment II, the mice were daily given 0.1 microg TCDD/kg body weight, with or without supplemental 2,000 IU vitamin A/kg body weight, and were killed on day 14, 28, and 42. In both experiments, TCDD significantly decreased the hepatic all-trans-retinol level and increased the hepatic all-trans-retinoic acid (RA) content, increased the mRNA and enzymatic activities of retinal oxidase. In TCDD + vitamin A mice, the all-trans retinol content was significantly higher, and the retinal oxidase mRNA was significantly lower on day 3 or 7 in Experiment I and on day 14 in Experiment II, compared to TCDD-treated mice. The induction of the retinal oxidase may contribute to the decrease in hepatic all-trans-retinol level and the increase in hepatic all-trans-RA caused by TCDD. Supplemental vitamin A might decelerate the effect of TCDD on retinal oxidase mRNA.     

Electromagnetic exposure effects the hippocampal dentate cell proliferation in gerbils (Meriones unguiculatus)

The chronic effect on hippocampal neurogenesis after exposure (30 min/day for 14 days) to a high frequency (35,53 kHz) electromagnetic field, double modulated at extremely low frequencies (ELF; 1, 8, 12, 29 and 50 Hz), was studied in young adult gerbils. Immediately after the last exposure proliferation of dentate granule cells was identified by in vivo labeling with 5-bromo-2-desoxyuridine (BrdU). Exposure to 1, 29 and 50 Hz resulted in a statistically significant reduction of cell proliferation rates, but only the 50 Hz-group manifested the effect highly significantly (-29,3 %). On the other hand, gerbils exposed to 8 and 12 Hz showed no significant change of postmitotic cell proliferation as compared with the sham treated controls. The results suggest that the effects of ELF on the granule cell proliferation are mediated by neurotransmitters and hormones which regulate hippocampal neurogenesis.     

Prenatal TCDD causes persistent modulation of the postnatal immune response, and exacerbates inflammatory disease, in 36-week-old lupus-like autoimmune SNF1 mice

BACKGROUND: Prenatal exposure to the persistent environmental pollutant and model Ah receptor agonist, 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD), has been shown to permanently suppress postnatal cell‐mediated immunity. More recently, skewing of select adult T and B cell responses toward enhanced inflammation has also been described in C57BL/6 mice after prenatal TCDD. This raises questions about adverse postnatal immune consequences of prenatal TCDD in animals genetically predisposed to inappropriate inflammatory responses. METHODS: Lupus‐prone SNF₁ mice were exposed to 0, 40, or 80 µg/kg TCDD on gestation day (gd) 12 and examined at 36 weeks‐of‐age for immunomodulatory effects that correlated with worsened lupus pathology. RESULTS: Bone marrow pro‐ and large pre‐B cells were decreased by prenatal TCDD, in both adult male and female mice, as were pre‐ and immature B cells. Splenic CD23⁻CD1^hi and CD19⁺CD5⁺ B cells were increased in males, as were B220^hi B cells in females, further suggesting persistent disruption of B cell lymphopoiesis by prenatal TCDD. Female mice displayed decreased IL‐10 production by ConA‐activated splenocytes, while males underproduced IL‐4. Autoreactive CD4⁺Vβ17a⁺ spleen T cells were increased in both sexes by 80 µg/kg TCDD. Male mice but not females showed increased anti‐ds DNA and cardiolipin autoantibody levels. CONCLUSIONS: Prenatal TCDD augmented the hallmark indicators of SLE progression in the lupus‐prone SNF₁ mice, including renal immune complex deposition, glomerulonephritis, and mesangial proliferation. Prenatal TCDD therefore caused persistent modulation of the postnatal immune response, and exacerbated inflammatory disease, in lupus‐like autoimmune SNF₁ mice. Birth Defects Res (Part B) 92:82–94, 2011. © 2011 Wiley‐Liss, Inc.     

The effect of progesterone administration on the expression of metastasis tumor antigens (MTA1 and MTA3) in placentas of normal and dexamethasone-treated rats

Background

Dexamethasone (DEX) induces intrauterine growth restriction (IUGR) in pregnant rats. IUGR can occur due to apoptosis of trophoblasts, which is believed to be inhibited by progesterone (P4). A group of genes called MTAs play a role in proliferation and apoptosis. MTA1 upregulates trophoblasts proliferation and differentiation, while MTA3 downregulates proliferation and induces apoptosis. Hence, we hypothesized that during IUGR, placental MTA1 decreases and MTA3 increases and this is reversed by P4 treatment.

Methods

Pregnant Sprague–Dawley rats were divided into 4 groups based on daily intraperitoneal injections: control (C, saline), DEX (DEX, 0.2 mg/kg/day), DEX and P4 (DEX?+?P4, DEX: 0.2 mg/kg/day, P4: 5 mg/kg/day) and P4-treated (P4, 5 mg/kg/day) groups. Injections were started on 15 dg until the day of dissection (19 or 21 dg). Gene and protein expressions of MTA1 and MTA3 were studied in the labyrinth (LZ) and basal (BZ) zones using real-time PCR and Western blotting, respectively.

Results

DEX treatment induced 18% reduction in fetal body weight (p?<?0.001) and 30% reduction in placental weight (p?<?0.01). Maternal P4 level was also significantly lower in DEX treated groups (p?<?0.05). MTA1 expression was decreased in the LZ (gene, p?<?0.001) and BZ (protein p?<?0.01), while MTA3 protein expression was upregulated in the LZ with DEX treatment (p?<?0.001). These changes were reversed with P4 treatment.

Conclusion

The findings of the present study indicate that DEX induces IUGR through changing the expression of placental MTA1 and MTA3 antigens and P4 improved pregnancy outcome by preventing the changes in MTAs expression.

     

Type II epithelial cells are critical target for hyperoxia-mediated impairment of postnatal lung development

Type II epithelial cells are essential for lung development and remodeling, as they are precursors for type I cells and can produce vascular mitogens. Although type II cell proliferation takes place after hyperoxia, it is unclear why alveolar remodeling occurs normally in adults whereas it is permanently disrupted in newborns. Using a line of transgenic mice whose type II cells could be identified by their expression of enhanced green fluorescent protein and endogenous expression of surfactant proteins, we investigated the age-dependent effects of hyperoxia on type II cell proliferation and alveolar repair. In adult mice, type II cell proliferation was low during room air and hyperoxia exposure but increased during recovery in room air and then declined to control levels by day 7. Eight weeks later, type II cell number and alveolar compliance were indistinguishable from those in room air controls. In newborn mice, type II cell proliferation markedly increased between birth and postnatal day 7 before declining by postnatal day 14. Exposure to hyperoxia between postnatal days 1 and 4 inhibited type II cell proliferation, which resumed during recovery and was aberrantly elevated on postnatal day 14. Eight weeks later, recovered mice had 70% fewer type II cells and 30% increased lung compliance compared with control animals. Recovered mice also had higher levels of T1alpha, a protein expressed by type I cells, with minimal changes detected in genes expressed by vascular cells. These data suggest that perinatal hyperoxia adversely affects alveolar development by disrupting the proper timing of type II cell proliferation and differentiation into type I cells.     

Pharmacokinetics of ovarian steroids in Sprague-Dawley rats after acute exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces abnormalities in steroid-dependent processes such as mammary cell proliferation, gonadotropin release and maintenance of pregnancy. In the current study, the effects of TCDD on the pharmacokinetics of 17beta-estradiol and progesterone were examined. Adult Sprague-Dawley rats were ovariectomized and pretreated with TCDD (15 microg/kg p.o.) or vehicle. A single bolus of 17beta-estradiol (E2, 0.3 micromol/kg i.v.) or progesterone (P4, 6 micromol/kg i.v.) was administered 24 hours after TCDD and blood was collected serially from 0-72 hours post-injection. Intravenous E2 and P4 in DMSO vehicle had elimination half-lives of approximately 10 and 11 hours, respectively. TCDD had no significant effect on the pharmacokinetic parameters of P4. The elimination constant and clearance of E2 were decreased by TCDD while the elimination half-life, volume of distribution and area under the time*concentration curve were not altered significantly. Overall, these results indicate that diminished serum progesterone and estradiol concentrations following exposure to TCDD are due primarily to actions on steroid synthesis and release rather than any alterations in pharmacokinetics.