Gonadal development and fertility of mice treated prenatally with cadmium during the early organogenesis stages

Paternal cadmium exposure affects testosterone synthesis by reducing the testicular cholesterol pool in offspring mice

Cadmium（Cd） is a heavy metal that is harmful to human health. Early studies have shown that cadmium can damage testicular structure, affecting testosterone synthesis and spermatogenesis. However, the effect of paternal Cd exposure on the reproductive system of offspring remains unclear. In this study, male 8-week C57BL/6 J mice were used as research objects, and Cd was injected intraperitoneally every other day at a dose of 1 mg/kg for 5 weeks, after which the effect on the reproductive system of offspring male mice was studied. Our results showed that the body weight of the offspring male mice increased faster, with increases of the testicular and epididymis indices under Cd exposure. At the same time, the serum testosterone and free cholesterol decreased, total cholesterol increased, and the sperm concentration decreased. Further qRT-PCR and western blot analyses showed that the expressions of StAR, P450scc, 3β-HSD and 17β-HSD, which are related to testosterone synthesis, was significantly downregulated. Additionally, ATGL, LDLR and SR-BI, which are related to the intracellular cholesterol pool were downregulated, leading to the reduction of the cholesterol pool and the accumulation of lipid droplets. Oil red O and BODIPY staining revealed an increase in the abundance of lipid droplets in testicular tissue of newborn and adult mice. Prediction of tsRNA target genes in the sperm of parents and testicular transcriptome of newborn mice showed that the differentially expressed genes were associated with catabolism of fatty acids, cholesterol and ion channels, while the mitochondrial and lysosome functions of testicular tissue of adult offspring mice were decreased. Overall, our results suggest that paternal Cd exposure reduced the intracellular cholesterol pool of testicular of offspring, affected testosterone synthesis and reproductive system development.

Metal(loid)s and human semen quality: The LIFE Study

Multiple studies have demonstrated a global population-wide decline in semen quality, with sperm concentrations having fallen 50 % over the past 50 years. Several metal and metalloid ("metal(loid)") compounds are known to have testicular toxicity, raising concerns about their contribution to rising infertility. In the male reproductive tract, metal(loid)s can reduce semen quality and disturb function both directly, by inducing tissue damage, and indirectly, by disrupting hormone production and secretion. This study assessed associations between 15 creatinine-adjusted metal(loid)s and 7 measures of semen quality among 413 reproductive-aged men recruited from 16 U.S. counties between 2005-2009. Multi-metal(loid) multivariable linear regression models estimated associations between semen quality endpoints and urinary concentrations of chromium, cobalt, copper, molybdenum, selenium, zinc, antimony, arsenic, barium, cadmium, lead, thallium, tin, tungsten, and uranium. LASSO regression was employed to select model variables and account for multicollinearity of the metal(loid)s. A positive association was observed between tin and sperm morphology (β = 4.92 p = 0.045). Chromium (β = 1.87, p = 0.003) and copper (β= -1.30, p = 0.028) were positively and negatively associated with total sperm count, respectively. With respect to DNA fragmentation, cadmium (β = 12.73, p = 0.036) was positively associated and chromium was negatively associated (β = -5.08, p = 0.001). In this cohort of U.S. population-based men, there was evidence of both positive and negative associations between specific metal(loid)s and semen quality. Additional research is needed to determine interactions between metal(loid)s within a mixture, consistent with typical human exposure, and identify sperm effects resulting from cumulative metal(loid) exposures.

Multigenerational effects of cadmium on the lifespan and fertility of Drosophila melanogaster

Although the damage and tolerance mechanisms of Cd stress are known, the data on genetic risk are limited. The aim of this study was to assess the chronic toxicity of Cd, genetic responses, and multigenerational effects in five generations of Drosophila melanogaster. For each generation, lifespan and fertility were statistically analysed and the expression of apoptosis- (p53 and caspase-3) and epigenesis-related (dDnmt2 and dMBD2/3) genes was examined. Lifespan and fertility significantly declined under Cd stress and these effects were maintained for two generations and one generation, respectively, when Cd stress was removed. The expression of p53 and caspase-3 was significantly up-regulated after exposure, suggesting that apoptosis contributes to the resistance mechanism. Their altered expression was retained for two generations. Furthermore, high expression of dDnmt2 and dMBD2/3 accompanied Cd exposure, which was passed on to three generations, suggesting that genetic modifications in apoptosis-related genes are carried to the offspring through epigenetic regulation.

Cadmium in Seminal Plasma of Fertile and Infertile Male Dromedary Camels

The objective of this study was to investigate the cadmium (Cd) profile in seminal plasma of male dromedary camel with impotentia generandi (post-coital infertility, IG group, n = 14) in comparison with known fertile males (FERT group, n = 5). Andrological examination was carried out for all animals. Semen was collected with electroejaculation and examined for volume, concentration, motility, viability, and abnormality. Seminal fluid was harvested after centrifugation and analyzed for Cd using atomic absorption spectrophotometer. Results showed that sperm concentration, motility, and viability were higher, while sperm abnormality was lower in IG group than in FERT group (P < 0.05). Cd was higher in seminal plasma of IG group than in FERT group (P = 0.04). Negative correlation was found between Cd concentration and sperm concentration (r = - 0.511, P = 0.04). There was also a tendency for negative correlation between Cd concentration and the testicular size (r = - 0.455, P = 0.05). In conclusion, Cd may be one of factors causing infertility in male dromedary camels.

Phthalate-Induced Fetal Leydig Cell Dysfunction Mediates Male Reproductive Tract Anomalies

Male fetal Leydig cells in the testis secrete androgen and insulin-like 3, determining the sexual differentiation. The abnormal development of fetal Leydig cells could lead to the reduction of androgen and insulin-like 3, thus causing the male reproductive tract anomalies in male neonates, including cryptorchidism and hypospadias. Environmental pollutants, such as phthalic acid esters (phthalates), can perturb the development and differentiated function of Leydig cells, thereby contributing to the reproductive toxicity in the male. Here, we review the epidemiological studies in humans and experimental investigations in rodents of various phthalates. Most of phthalates disturb the expression of various genes encoded for steroidogenesis-related proteins and insulin-like 3 in fetal Leydig cells and the dose-additive effects are exerted after exposure in a mixture.

Impotentia generandi in male dromedary camels: heavy metal and trace element profiles and their relations to clinical findings and semen quality

The aim of this study was to investigate the profiles of cadmium (Cd), lead (Pb), selenium (Se), zinc (Zn), copper (Cu), molybdenum (Mo), iron (Fe), and manganese (Mn) in serum of dromedary camels with impotentia generandi and their associations with the clinical findings and semen analysis data. Sixteen male dromedary camels with impotentia generandi (IG group) and 5 fertile camels (FERT group) were used. The external and internal genital organs were examined using visual inspection, palpation, and ultrasonography. Semen was collected by electroejaculation and examined for volume, count, motility, viability, and abnormality. Blood was collected from all camels and serum was harvested. All serum samples were digested by concentrated acids and analyzed for heavy metals and trace elements by flame emission atomic absorption spectrophotometer. Results showed that the mean heavy metal and trace element concentrations in serum were in the following descending order Fe > Zn > Cu > Cd > Mo > Se > Mn > Pb. Cd was higher in IG than in FERT males (P = 0.02). Se was greater in FERT than in IG groups (P = 0.003). Zn was higher in in FERT than in IG groups (P = 0.001). There were positive correlations between Zn and sperm count (r = 0.59, P = 0.005) and sperm motility (r = 0.57, P = 0.005) and a tendency for negative correlation between Zn and sperm abnormalities (r = - 0.44, P = 0.05). In conclusion, Cd might be implicated as a cause of infertility in male camels. Deficiencies of Se and Zn may also have adverse impacts on male camel reproduction.

The environment and male reproduction: The effect of cadmium exposure on reproductive function and its implication in fertility

Cadmium is an environmental pollutant known as endocrine disruptor. Testis is particularly susceptible to cadmium, and testis injury occurs at high but even low levels of exposure. Cadmium reproductive toxicity is mediated by multiple mechanisms, including structural damage to testis vasculature and blood-testis barrier, inflammation, cytotoxicity on Sertoli and Leydig cells, oxidative stress mainly by means of mimicry and interference with essential ions, apoptosis, interference with selected signaling pathways and epigenetic regulation of genes involved in the regulation of reproductive function, and disturbance of the hypothalamus-pituitary-gonadal axis. The current review outlines epidemiological observational findings from environmental and occupational exposure in humans, and reports experimental studies in humans and animals. Lastly, a focus on the pathogenetic mechanisms of cadmium toxicity and on the specific mechanisms of cadmium sensitivity and resistance, particularly assessed in animal models, is included. Despite convincing experimental findings in animals and supporting evidences in humans identifying cadmium as reproductive toxicant, observational findings are controversial, suffering from heterogeneity of study design and pattern of exposure, and from co-exposure to multiple pollutants.

Protective Effect of Fragaria ananassa Crude Extract on Cadmium-Induced Lipid Peroxidation, Antioxidant Enzymes Suppression, and Apoptosis in Rat Testes

Cadmium is a deleterious environmental pollutant that threats both animals and human health. Oxidative stress and elevated levels of reactive oxygen species (ROS) have recently been reported to be the main cause of cellular damage as a result of cadmium exposure. We investigate, here, the protective effect of strawberry crude extracts on cadmium-induced oxidative damage of testes in rats. Four groups (n = 8) of 32 adult male Wistar rats weighing 160-180 g were used. The control group received 0.9% saline solution all over the experimental period (5 days). Group 2 was intraperitoneally injected with 6.5 mg/kg CdCl₂. Group 3 was provided only with an oral administration of strawberry methanolic extract (SME) at a dose of 250 mg/kg. Group 4 was treated with SME before cadmium injection with the same mentioned doses. It was shown that cadmium exposure results in a significant decrease in both relative testicular weight and serum testosterone level. Analyzing the oxidative damaging effect of cadmium on the testicular tissue revealed the induction of oxidative stress markers represented in the elevated level of lipid peroxidation (LPO), nitric oxide (NO), and a decrease in the reduced glutathione (GSH) content. Considering cadmium toxicity, the level of the antioxidant enzyme activities including catalase (CAT), superoxide dismutase (SOD2), glutathione peroxidase (GPx1), and glutathione reductase (GR) were markedly decreased. Moreover, gene expression analysis indicated significant upregulation of the pro-apoptotic proteins, bcl-2-associated-X-protein (BAX), and tumor necrosis factor-α (TNFA) in response to cadmium intoxication, while significant downregulation of the anti-apoptotic, B-cell lymphoma 2 (BCL2) gene was detected. Immunohistochemistry of the testicular tissue possessed positive immunostaining for the increased level of TNF-α, but decreased number of proliferating cell nuclear antigen (PCNA) stained cells. Administration of SME debilitated the deleterious effect of cadmium via reduction of both LPO and NO levels followed by a significant enhancement in the gene expression level of CAT, SOD2, GPX1, GR, nuclear factor-erythroid 2-related factor 2 (NFE2L2), heme oxygenase-1 (HMOX1), Bcl-2, and PCNA. In addition, the SME treated group revealed a significant increase in the level of testosterone and GSH accompanied by a marked decrease in the gene expression level of Bax and TNF-α. In terms of the summarized results, the SME of Fragaria ananassa has a protective effect against cadmium-induced oxidative damage of testes.

Protective role of zinc against the toxicity induced by exposure to cadmium during gestation and lactation on testis development

To assess the effects of exposure to Cd and Zn on rat testicular development, offspring, from mothers receiving either tap water, Cd, Zn or Cd+Zn during gestation and lactation periods, were observed on gestational day (GD) 20 and on postnatal days (PND) 12, 21 and 35. During gestation, Cd induced maternal hypozincemia and less transfer of Zn to the fetus. During lactation, progressive Cd accumulation and Zn depletion in testis at PND12 and PND21 were noted. An increase of abnormal seminiferous tubules and a decrease in testis weight and plasmatic testosterone concentration were also observed at PND21 and PND35 respectively. Interestingly, Zn supply induced a significant protection against Cd toxicity. These results suggest that the toxic effects of Cd observed during development are mediated by the disruption of Zn metabolism, which is established in mothers during pregnancy causing Zn deficiency in fetuses and continues to become more pronounced during lactation.

Concerns about the widespread use of rodent models for human risk assessments of endocrine disruptors

Fetal testis is a major target of endocrine disruptors (EDs). During the last 20 years, we have developed an organotypic culture system that maintains the function of the different fetal testis cell types and have used this approach as a toxicological test to evaluate the effects of various compounds on gametogenesis and steroidogenesis in rat, mouse and human testes. We named this test rat, mouse and human fetal testis assay. With this approach, we compared the effects of six potential EDs ((mono-(2-ethylhexyl) phthalate (MEHP), cadmium, depleted uranium, diethylstilboestrol (DES), bisphenol A (BPA) and metformin) and one signalling molecule (retinoic acid (RA)) on the function of rat, mouse and human fetal testis at a comparable developmental stage. We found that the response is similar in humans and rodents for only one third of our analyses. For instance, RA and MEHP have similar negative effects on gametogenesis in the three species. For another third of our analyses, the threshold efficient concentrations that disturb gametogenesis and/or steroidogenesis differ as a function of the species. For instance, BPA and metformin have similar negative effects on steroidogenesis in human and rodents, but at different threshold doses. For the last third of our analyses, the qualitative response is species specific. For instance, MEHP and DES affect steroidogenesis in rodents, but not in human fetal testis. These species differences raise concerns about the extrapolation of data obtained in rodents to human health risk assessment and highlight the need of rigorous comparisons of the effects in human and rodent models, when assessing ED risk.

Childhood cancer and traffic-related air pollution exposure in pregnancy and early life

BACKGROUND

The literature on traffic-related air pollution and childhood cancers is inconclusive, and little is known on rarer cancer types.

OBJECTIVES

We sought to examine associations between childhood cancers and traffic-related pollution exposure.

METHODS

The present study included children < 6 years of age identified in the California Cancer Registry (born 1998-2007) who could be linked to a California birth certificate (n = 3,590). Controls were selected at random from California birthrolls (n = 80,224). CAlifornia LINE Source Dispersion Modeling, version 4 (CALINE4) was used to generate estimates of local traffic exposures for each trimester of pregnancy and in the first year of life at the address indicated on the birth certificate. We checked our findings by additionally examining associations with particulate matter (≤ 2.5 μm in aerodynamic diameter; PM2.5) pollution measured by community-based air pollution monitors, and with a simple measure of traffic density.

RESULTS

With unconditional logistic regression, a per interquartile range increase in exposure to traffic-related pollution during the first trimester (0.0538 ppm carbon monoxide, estimated using CALINE4) was associated with acute lymphoblastic leukemia [ALL; first trimester odds ratio (OR) = 1.05; 95% CI: 1.01, 1.10]; germ cell tumors (OR = 1.16; 95% CI: 1.04, 1.29), particularly teratomas (OR = 1.26; 95% CI: 1.12, 1.41); and retinoblastoma (OR = 1.11; 95% CI: 1.01, 1.21), particularly bilateral retinoblastoma (OR = 1.16; 95% CI: 1.02, 1.33). Retinoblastoma was also associated with average PM2.5 concentrations during pregnancy, and ALL and teratomas were associated with traffic density near the child's residence at birth.

CONCLUSIONS

We estimated weak associations between early exposure to traffic pollution and several childhood cancers. Because this is the first study to report on traffic pollution in relation to retinoblastoma or germ cell tumors, and both cancers are rare, these findings require replication in other studies.

Cadmium increases human fetal germ cell apoptosis

BACKGROUND

Cadmium (Cd) is a common environmental pollutant and a major constituent of tobacco smoke. Adverse effects of this heavy metal on reproductive function have been identified in adults; however, no studies have examined its effects on human reproductive organs during development.

OBJECTIVES

Using our previously developed organ culture system, we investigated the effects of cadmium chloride on human gonads at the beginning of fetal life, a critical stage in the development of reproductive function.

METHODS

Human fetal gonads were recovered during the first trimester (711 weeks postconception) and cultured with or without Cd. We used different concentrations of Cd and compared results with those obtained with mouse fetal gonads at similar stages.

RESULTS

Cd, at concentrations as low as 1 microM, significantly decreased the germ cell density in human fetal ovaries. This correlated with an increase in germ cell apoptosis, but there was no effect on proliferation. Similarly, in the human fetal testis, Cd (1 microM) reduced germ cell number without affecting testosterone secretion. In mouse fetal gonads, Cd increased only female germ cell apoptosis.

CONCLUSIONS

This is the first experimental demonstration that Cd, at low concentrations, alters the survival of male and female germ cells in humans. Considering data demonstrating extensive human exposure, we believe that current environmental levels of Cd could be deleterious to early gametogenesis.

Occupational hazards to male fecundity

Research methods and knowledge in the field of male reproductive toxicology have gradually improved since reports in the late 1970s on severe impairment of spermatogenesis in workers with occupational exposure to certain chlorinated hydrocarbon pesticides (the nematocide 1,2-dibromochloropropan and the insecticide and fungicide chlordecone, but still we have only vague answers to basic questions about the overall significance of the environmental and occupational impact of these compounds on male reproductive capability.

The effects of metals as endocrine disruptors

This review reports current knowledge regarding the roles that cadmium (Cd), mercury (Hg), arsenic (As), lead (PB), manganese (Mn), and zinc (Zn) play as endocrine-disrupting chemicals (EDCs). The influence of these metals on the endocrine system, possible mechanisms of action, and consequent health effects were correlated between experimental animals and humans. Analysis of the studies prompted us to identify some critical issues related to this area and showed the need for more rigorous and innovative studies. Consequently, it was recommended that future studies need to: (1) identify the mechanisms of action, because at the present time only a few have been elucidated-in this context, the possible presence of hormesis need to be determined, as currently this was reported only for exposure Cd and As; (2) study the possible additive, synergistic, or antagonistic effects on the endocrine system following exposure to a mixture of metals since there is a lack of these studies available, and in general or occupational environments, humans are simultaneously exposed to different classes of xenobiotics, including metals, but also to organic compounds that might also be EDCs; (3) assess the potential adverse effects on the endocrine system of low-level exposures to metals, as most of the information currently available on EDCs originates from studies in which exposure levels were particularly high; and (4) assess the effects on the endocrine and reproductive systems of other metals that are present in the general and occupational environment that have not yet been evaluated.

Prenatal Exposure to Diesel Exhaust Impairs Mouse Spermatogenesis

The effect of prenatal exposure to diesel exhaust (DE) was investigated. Twenty pregnant ICR mice were exposed to DE at the particle concentration of 1.0 mg/m3, from d 2 until d 16 postcoitum. Male offspring were kept alive until 12 wk of age, and then male reproductive organ weight, daily sperm production (DSP), serum testosterone level, and mRNA expression of sex steroid hormone synthesis process-related factors were measured. Serum testosterone levels of the exposed group were reduced significantly at 3 wk, whereas they were elevated significantly at 12 wk. DSP was also markedly reduced at 5 and 12 wk. Histological examination showed multinucleated giant cells in the seminiferous tubules of the exposed group as well as partial vacuolation of the seminiferous tubules. Follicle-stimulating hormone receptor (FSHR) mRNA expression and steroidogenesis acute regulatory (StAR) protein were significantly increased at 5 wk and 12 wk, respectively. This study suggests that prenatal exposure to DE has detrimental effects on mouse spermatogenesis in offspring.

Effect of cadmium on gonadal development in freshwater turtle (Trachemys scripta, Chrysemys picta) embryos

Prior studies on painted turtle (Chrysemys picta) sub-populations near the Massachusetts Military Reservation (MMR), a Superfund site on Cape Cod, Massachusetts, USA, suggest several reproductive deficits which may be related to xenobiotics. Several heavy metals, including cadmium, have been detected in Cape Cod surface water and sediments. The present study was carried out to investigate the effect of an environmentally relevant dose of cadmium on gonadal development during the end of the germ cell migration phase and post-natal gonadal maturation in freshwater turtles. Comparison of cadmium concentration in eggs of C. picta from Cape Cod showed that eggs from the impacted site animals had significantly higher cadmium in yolk than eggs from the reference site animals (7.23 +/- 1.95 ng/g vs. 1.31 +/- 0.50 ng/g). Gonadal structure and the number of proliferating germ cells of neonates derived from eggs of adult females from these sites showed no marked difference between sites. However, apoptosis of oocytes was significantly increased in neonate C. picta from the impacted pond compared to the reference pond. The effect of an administered environmentally relevant dose of cadmium on germ cell number and oocyte apoptosis was subsequently assessed in lab-reared Trachemys scripta, a closely related freshwater turtle species. Assessment of isotopic cadmium transmission showed that 6.29% of cadmium applied to the eggshell was transmitted through the eggshell to the yolk. The results showed that the total number of germ cells in cadmium-treated (1 microg/g) embryos was less than half that found in control embryos. The reduced germ cell number in Cd-treated embryos suggests that cadmium may reduce proliferation and/or delay migration of germ cells to the genital ridge. The effects of cadmium on turtle gonadal development were found to extend into 3 months post hatch. Proliferation of oocytes was not influenced by exposure to cadmium in ovo. In contrast, apoptosis of oocytes was significantly increased in cadmium exposed T. scripta. Since a lesion at the gonial stages will lead eventually to the depletion of more mature germ cells, the results for neonate turtles suggest that an environmental impact due to a xenobiotic mixture may enhance the rate of apoptosis, thus resulting in the reduction in follicle number seen in adult turtles from the impacted site. Overall, the data provide evidence that environmentally relevant doses of cadmium may affect gonadal developmental processes of freshwater turtles during embryonic and post-natal stages that may result in disruption of reproductive processes later in life.

X-chromosome activity of the mouse primordial germ cells revealed by the expression of an X-linked lacZ transgene

We have determined the timing of the inactivation and reactivation of the X chromosome in the mouse primordial germ cells (PGCs) by monitoring the expression of an X-linked HMG-lacZ reporter gene. PGCs were identified by their distinct alkaline phosphatase activity and they were first localised in the primitive streak and allantoic bud of the 7.5-day gastrulating embryo. Although inactivation of the transgene was found in some PGCs at these sites, at least 85% of the population were still expressing the lacZ gene. This suggests that, although X-inactivation has commenced during gastrulation, the majority of PGCs still possess two active X chromosomes. Transgene activity remained unchanged during the relocation of PGCs to the hindgut endoderm, but decreased abruptly when PGCs left the hindgut and migrated through the mesentery. X-inactivation was completed during the migration of PGCs, but not simultaneously for the whole population. The first wave of PGCs entering the genital ridge at 9.5 days did not immediately re-activate the silent transgene until about 24 hours later. Re-activation of the transgene took place in over 80% of PGCs entering the genital ridge at 10.5-13.5 days p.c., preceding the entry into meiosis. About 90% of the meiotic germ cells in the 14.5-15.5 day fetal ovary expressed the transgene. Similar profiles of transgene activity were observed in PGCs of embryos that have inherited the lacZ transgene from different parents, showing unequivocally that X-inactivation in the germ cell lineage is not related to parental legacy.(ABSTRACT TRUNCATED AT 250 WORDS)

Potential human developmental toxicants and the role of animal testing in their identification and characterization

Some 50 chemicals have been identified from environmental, occupational, or therapeutic exposure data as being potential developmental toxicants in humans. The toxicity pattern of these chemicals in humans has been characterized and correlated with developmental toxicity end points in laboratory animal models in order to determine the relevance and predictiveness of the results of testing in animals in extrapolation to human data. In general, animal developmental toxicity data closely paralleled human outcomes, and while humans in most cases were more sensitive than animals, the data support the concept that, imperfections aside, studies in animals serve a vital role in the hazard identification process.

Postimplantation development of mitomycin C-treated mouse blastocysts

Treatment of morula-stage mouse embryos with mitomycin C (0.004-0.5 microgram/ml) in vitro resulted in a decrease in the number of inner cell mass (ICM) cells at the blastocyst stage. The trophectoderm population was reduced only at the highest dosage (0.5 microgram/ml) tested. Postblastocyst development in vitro was retarded: Fewer embryos formed trophoblastic outgrowth, and the ICM was poorly developed. The embryo transfer experiments demonstrated that a reduction in ICM cell numbers diminished the potential of embryogenesis. The presence of a sufficient number of trophoblasts and ICM cells in the blastocyst is therefore a prerequisite for successful implantation and embryogenesis. The mitomycin-treated blastocysts with only 70% of normal ICM cells developed to egg cylinders that were about half normal size, but by days 12-14 the body size of the surviving embryo was similar to that of the control embryo. Morphogenesis was retarded during the early organogenesis stages, but only a slight delay was seen in the treated embryo on day 12. Such observation strongly suggests that a restorative phase of growth and morphogenesis has occurred during the immediate postimplantation period.

Zinc amelioration of cadmium toxicity on preimplantation mouse zygotes in vitro

Zinc, at a concentration of 5 or 10 micrograms/ml medium, has been shown to protect mouse preembryos in vitro from the toxicity of cadmium at a concentration of 5 micrograms/ml medium after a simultaneous treatment of the ions from four-cell to morula or from morula to blastocyst for 24 hours. Such an amelioration indicates that cadmium toxicity is a result of the unique property of the cadmium ion and is not due to an alteration in the culture medium after the addition of an extra metallic ion. Zinc probably ameliorates cadmium-treated mouse preembryo by competing with cadmium for uptake or some other metabolic processes. In view of the well-documented competition between cadmium and zinc ions for binding sites in many other cell types, some macromolecules to which similar divalent metallic ions bind competitively may also exist in the mouse preembryo. This suggests that a protective mechanism dependent on the metal-metal interactions begins to operate in the mouse preembryo at a very early stage of differentiation before implantation.

Migration and proliferation of primordial germ cells in the rat

Information about early primordial germ cell (PGC) formation and migration in rats is lacking. In utero developed and in vitro cultivated whole rat embryos were studied on days 10-13 postcoitum (p.c.). The development of the PGCs was investigated in serial sections stained for alkaline phosphatase activity. On postcoital day 10, PGCs were found in the invaginating visceral yolk sac endoderm and at the base of the allantois. At day 11 p.c. PGCs were mostly found in the ventral and lateral gut wall or in the mesenchyme between the gut and the future genital ridges. At day 12 p.c. most of the PGCs (94%) could be localised in the mesenchyme or in the future genital ridges. On postcoital day 13 almost all PGCs had reached the now-well-developed genital ridges. Quantitative measurements showed an increase in the number of PGCs from 84 at day 10 p.c. up to 2,768 at day 13 p.c. Only slight differences were found between in vivo and in vitro embryos with respect to the number of PGCs and their developmental pattern. The in vitro culture of whole rat embryos enables the discrimination between the effects of indirect (maternal) and direct action of PGC-toxic agents.

Effects of cadmium on preimplantation and early postimplantation mouse embryos in vitro with special reference to their trophoblastic invasiveness

Cadmium chloride, at concentrations of 0.5 or 1 microgram/ml medium, did not affect the trophoblastic invasiveness of mouse embryos treated for 24 hours at 4-cell and morula stages. At higher concentrations of 5 or 10 micrograms/ml medium, most treated embryos in vitro underwent degeneration while a few survivors formed trophoblastic outgrowths with variable areas. Cadmium chloride, at a low concentration of 0.5 microgram/ml medium presented continuously to blastocysts after attachment in vitro, has significantly retarded the trophoblastic outgrowth areas and reduced the number of trophoblastic giant-cell nuclei, though the spreading blastocysts appeared morphologically normal. At higher concentrations of 1 or 5 micrograms/ml medium, cytoplasmic disintegration and detachment of trophoblasts were observed. It is suggested that cadmium may interfere with the cell division and/or the transformation of trophectoderm cells into giant cells, resulting in the retardation of the trophoblastic outgrowths.

Effects of cadmium on lactate dehydrogenase activities in mouse pre-embryos at various stages

A decline in LDH activity from four-cell to late blastocyst was demonstrated in pre-embryos from F1 (C57 female X A2G male) female mice. An exposure to 0.5 or 1 microgram/ml cadmium did not affect the in vitro development of the four-cell pre-embryos and morulae or their LDH activities. At 5 or 10 micrograms/ml cadmium, the in vitro development of the treated pre-embryos was affected. Although most of the treated four-cell pre-embryos had proceeded to compaction, they became degenerated 24 h after treatment. The LDH activity of these degenerated pre-embryos was higher than that in the control blastocysts. We propose that cadmium may interfere with the general energy metabolism of the cells. This causes a reduced rate of LDH degradation, leading to a slower decline in LDH activity in cadmium-treated pre-embryos. Failure of some critical biochemical processes after cadmium treatment may ultimately lead to the subsequent degeneration of the treated pre-embryos.