James G. Wilson

DNA synthesis inhibition and cell death associated with hydroxyurea teratogenesis in rat embryos

Abstract A study of the embryotoxic and DNA synthesis inhibiting properties of hydroxyurea on 12-day rat embryos is presented. A profound depression of DNA synthesis was evident after all doses studied including a nonteratogenic dose. The time required to return to control synthetic levels was roughly proportional to dosage. The finding of effective hydroxyurea levels in the embryo strengthens the idea of a direct effect on embryonic cells as the cause of malformations and reveals that embryo cells respond to similar concentrations of hydroxyurea as do other cell types. Finally, the ability of hydroxyurea to produce early cell death in localized areas of the rat embryo is shown. Extensive cell death in the limbbud is followed at term by malformations in that structure. Surprisingly, however, extensive cell death in the neural tube does not lead to gross malformations of the central nervous system.

Are female sex hormones teratogenic

An analysis of available epidemiologic data leads the present reviewers to conclude that the use of exogenous hormones during human pregnancy has not been proved to cause developmental abnormality in nongenital organs and tissues. This conclusion is further supported by the animal laboratory data. The preponderance of evidence at this writing indicates a lack of causal association between hormonal use during pregnancy and nongenital malformation of the offspring. The quality of the epidemiologic data does not, at this time, permit a definitive conclusion that sex hormones during pregnancy may not, under as yet to be defined conditions, have some adverse effect on human prenatal development. If there are increased risks of nongenital malformations associated with the administration of certain sex steroids, the risks are very small, may not be causal, and are substantially below the spontaneous risk of malformations. In spite of the present degree of uncertainty, the clinical, epidemiologic, and laboratory data do permit the formulation of a rational approach to handling problems related to sex steroid usage and exposure in pregnant women.

Differentiation as a determinant of the reaction of rat embryos to X-irradiation.

Summary X-irradiation of rat embryos on the 8th day of gestation had a more limited effect on subsequent development than did similar treatment on the 9th and 10th days. The only residual effect after doses of 121/2 to 100r on the 8th day was retardation of growth. Exposure to comparable doses on the 9th and 10th days has been shown previously to result in the development of malformations and in an increase in mortality, as well as in retardation of growth. This difference in reactivity appears to be dependent upon whether cellular differentiation within the embryos has begun at the time of irradiation.

Influence on the offspring of altered physiologic states during pregnancy in the rat.

I t is now well established that the course of embryonic development may occasionally be modified by environmental influences. The environment of the mammalian embryo can be thought of as consisting of two layers. First, there is the maternal body which provides remarkably constant physical and chemical surroundings for the embryo. Beyond the maternal body is what may be called the extramaternal part of the environment. This is not constant, but the fact is of little consequence because the maternal body is usually able to insulate the embryo against ordinary changes in the extramaternal environment. Only such uncommon influences as penetrating radiations are known to pass readily through the maternal barrier and directly affect the embryo. This is not to say that other intluences arising outside the mother do not affect the embryo, but such outside agents must be mediated by the maternal organism, and the probability exists that many of them act indirectly by inducing some modification in the physiologic state of the mother. Thus, virtually all environmental change to which the embryo is likely to be subjected either arises within the maternal body or is mediated by it. Regardless of whether internal or external in origin, changed physiologic states within the pregnant mother must have a place in any consideration of factors which may affect the offspring. Recent experiments and observations by several investigators have revealed that a number of agents are capable of acting on or through the pregnant mother to cause maldevelopment of her young. The varieties of these agents known a t the present time as well as the diverse organs and systems of the embryo upon which they act are presented in TABLE 1. Although an impressive array, the fact remains that in no instance is the manner of action upon the embryo known. In the case of vitamin A13 and pantothenic acid1 deficiencies, the observation that the fetuses exhibited some of the symptoms of postnatal deficiency has been cited as evidence of direct action on the fetus. In these as well as in the other situations listed, however, the mothers experienced more or less profound physiologic alterations. The alterations were usually numerous and interrelated and it was not possible to relate any one or combination of them to the effect observed in the young. Indeed, more than one recent writer, after reviewing these observations, has suggested that any physiologic stress placed upon the pregnant mother might result in maldevelopment of her young if the stress were sufficiently intense. In view of the need for further information on the subject, a series of experiments has been undertaken to study the types and degrees of maternal physiologic alterations capable of adversely influencing the development of the offspring. In general, a standardized procedure has been employed which calls for subjecting pregnant rats to a particular type of physiologic stress a t a

Studies on induction of polydactyly in rats with cytosine arabinoside

Cytosine arabinoside administered at appropriate times produced polydactyly of the forelimb (d.10) and rear limb (d.11) in the offspring of pregnant rats. Attempts to define the mechanism whereby an antiproliferative, cytotoxic agent could produce polydactyly centered on examination of proliferative rate in the rear limb following a regimen known to produce rear limb polydactyly in 85% of surviving fetuses. Tissues for [3H]thymidine autoradiography were taken 9–42 hr following drug administration. In control embryos, mesodermal cells in various regions of the limb appeared to proliferate at uniform rates until the 13th day when the proximal fields began to show diminished activity. Likewise, pre- and postaxial ectoderm of the limb seemed to be proliferating at equal rates in control embryos. A positive correlation in proliferative rate between the ectoderm and mesoderm was found to exist in control embryos, i.e., as one tissue increased or decreased in proliferative activity the other behaved in similar fashion. In treated embryos this correlation was absent. Treated embryos also revealed cell-cycle synchrony of both mesodermal and ectodermal cells although the time of peak DNA synthesis was different in the two tissues. n nHistologically, cytosine arabinoside produced cell degeneration especially in the mesoderm. Possibly of more importance was the finding of cell death in the preaxial ectoderm of control embryos late on the 12th day of development, whereas treated embryos of a similar age did not show a similar region of degeneration.

Congenital malformations produced by injecting azo blue into pregnant rats.

Summary The injection of 1 cc of a 1% aqueous solution of the diazo dye azo blue into female rats on the 7th, 8th and 9th days of pregnancy resulted in congenital malformations in 59% of living fetuses removed on the 20th day of gestation. The incidence was higher than that obtained with trypan blue (49%) under the same conditions, but the types of malformations were similar.

Influence of severe hemorrhagic anemia during pregnancy on development of the offspring in the rat.

Summary Pregnant rats were rendered severely anemic by permitting free bleeding from the freshly severed tail on 3 successive days. This frequently caused early termination of pregnancy as a result of maternal death or resorption of the entire litter, but litters from mothers surviving this treatment were essentially normal. Only when bleeding was begun on the 9th day was there a minimal effect on the offspring, manifested by malformations in 2.6% of the young, a mild degree of retardation of growth in 4 of 13 litters, and a slight increase above the normal rate of intrauterine resorption in litters reaching term. Since even these minimal effects were not observed after hemorrhage at other times during gestation, it is apparent that maternal hemorrhagic anemia represents no particular hazard to the offspring in surviving litters. This suggests that severe physiologic stresses during pregnancy, however severe, are not always capable of causing abnormality in the offspring.