Embryos vulnerabilities

Figure 9-5 The sensitivity of the conceptus to a theoretical teratogen during rat gestation (modified from 161). The most susceptible window is organogenesis with low levels of vulnerability at the time of implantation and the period of functional maturation. Superimposed are the approximations of when the developmental landmarks that are represented in the four in vitro tests occur. The chick embryo neural retina model (CENR) represents events around GD 10-13. The mouse embryonic stem cell test (EST) corresponds roughly to the period of GD 6-10 in the rat, near the peak of sensitivity. Whole embryo culture (WEC) recapitulates the window at the peak of sensitivity, between GD 9-11 or GD 10-12 depending upon the window within which the culture is conducted. Rabbit cultures are also done between GD 10-12. Represented by the single ( ) and double asterisk ( ), respectively, are the initiation and termination of the dosing period in regulatory compliant preclinical embryo/fetal toxicity studies. Thus, the zebrafish is the only model that permits exposure to test article during this important period.

Although embryos, fetuses, and nursing infants may be exposed to relatively high amounts of PCBs during sensitive periods of development, it is not known if the susceptibility of children to the health effects of PCBs differs from that of adults. Younger children may be particularly vulnerable to PCBs... 

In February 2008,200 researchers who had met the year before in Norway announced that embryos and fetuses are more vulnerable than previously thought to chemical pollutants that can cause disease or disability, and that embryos and fetuses are vulnerable even to extremely small doses that do not harm adults.17... 

It s important to note that not all developing embryos and fetuses have the same vulnerability to environmental lead. Given two individuals with the same blood lead concentration, it s possible that one individual will show clear symptoms of neurological damage while the other individual will show no clinical symptoms at all.24 We don t know why these differences in vulnerability exist or what the mechanisms are that determine... 

There is no evidence to argue that the other half result from prenatal environmental effects. But it s reasonable to assume that the prenatal environment in its various forms can be an important factor, and that countless possibilities exist for both lethal and nonlethal effects due to that factor. The simple fact that so many embryos are apparently lost means embryos are particularly vulnerable to damage. 

Weiss, B Amler, S., and Amler, R. W. (2(K)4). The vulnerability,. sensitivity, and resiliency of the developing embryo, infant, child, and adolescent to the effects of environmental chemicals, drugs, and physical agents as compared to the adult pesticides. Pediatrics 113(4, Pt2), 1030-1036. 

The current view is that embryos and fetuses may be especially vulnerable to environmental insult because of qualitative and/or quantitative differences from adults. These factors include ... 

The nucleotide patterns of cultured animal cells and ascites tumor cells are generally less vulnerable than those of tissues however, if washing is required, a medium capable of supporting energy metabolism should be employed. If cells are to be packed by centrifugation prior to extraction, cultures or ascitic fluids may first have to be cooled. Cells are extracted in the cold some procedures employ alternate freezing and thawing in the presence of acidic extractants. Extraction of cultured mouse embryo cells with 60% methanol for 16 hours at — 20 C has been employed in the analysis of deoxyribonucleoside triphosphates 9). 

The developing eye is not only highly vulnerable to vitamin A deficiency, but also an excess of exogenous RA is known to cause severe eye malformations [1, 2, 13, 25]. We analyzed the mechanism of retinoid-related ocular teratology and its normal correlate in early zebrafish and mouse embryos, and we conclude that for the proper formation of the ventro-dorsal retina dimension, the eye anlage has to contain both a RA-rich and a RA-poor region. 

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