Effects of vincristine on developing hamster embryos.

Using dosages and a route of administration which resembled those used clinically in humans, the effects of vincristine on developing hamster embryos were evaluated. The results showed that the drug exerted a highly toxic effect in a dose-dependent manner; however, it exhibited only a sporadic teratogenic (gross malformation) effect. The data on DNA synthesis indicated involvement of internal organs and structures, which needs to be verified. Overall, the teratogenicity of the drug was more pronounced during pre-organogenesis than during the organogenesis period. It was suggested that, in contrast to the data reported in the literature, the different biological response to vincristine in hamster may relate to the use of the dose-route combination, and is potentially relevant to developmental and transplacental carcinogenesis studies.

Palatal shelf reorientation in hamster embryos following treatment with 5-fluorouracil.

A study was undertaken to examine the issue of whether achieving a critical mass of cells and/or palatal shelf volume during vertical development of shelf is essential for reorientation to occur. In control and 5-fluorouracil (5FU)-treated hamster embryos' palatal shelves, at different times during gestation, the numbers of both epithelial and mesenchymal cells were counted and cross-sectional area was measured. DNA synthesis was measured by 3H-thymidine incorporation and was used as an index of growth by cell proliferation. The control data indicated that, unlike development during initial 24 hours, the later period of vertical palatal development was characterized by a steady level of mesenchymal and epithelial cell numbers and palatal shelf area. Following 5FU treatment all the measurements were reduced, and until they reached the equivalent of control values, the palatal shelves did not reorient. The density of mesenchymal cells in the developing palate did not seem to affect cell number. On the basis of the analysis of results of the present study, along with those reported in the literature, it is suggested that, in hamsters, acquisition and maintenance of both a specified number of mesenchymal cells and shelf area, at least 24 hours prior to reorientation, may be critical for ensuing mesenchymal differentiation to enforce palatal shelf reorientation on schedule. 5FU affected these features to delay reorientation of the palatal shelf.

Growth of the secondary palate in the hamster following hydrocortisone treatment: shelf area, cell number, and DNA synthesis.

The contribution made by mesenchymal cells during the later stages of palatal development was examined in control and hydrocortisone-treated hamster embryos. Cross-sectional area of the palatal shelf was measured, and the numbers of both epithelial and mesenchymal cells were counted. DNA synthesis was measured by 3H-thymidine incorporation and was used as an index of growth by cell proliferation. The observations in controls indicated that, unlike development during the initial 24 hr, the later period of vertical palate development, followed by reorientation of shelves and their closure, was characterized by a steady level of mesenchymal cell number and palatal shelf area. An absence of corresponding growth in the epithelial cell number suggests that the cells may accommodate the growth either by increasing their size and/or by stretching along the basal lamina. Hydrocortisone treatment did not alter the growth pattern of cell numbers or shelf area. However, it prevented the fusion between the opposing shelves, perhaps by affecting the cytodifferentiation of the palatal tissues. Although a continuous increase in the number of mesenchymal cells during the latter half of vertical shelf development, i.e., between days 11:00 and 12:00 of gestation, is not required for reorientation and fusion of the shelves, it is not clear from the data from the present study whether a critical number of cells and/or cell density is essential for reorientation and fusion of the palate. It was suggested that, for normal palatal development, information on cell cycle and positioning of mesenchymal cells within the shelf during the vertical development may be crucial for further understanding of subsequent events of palatogenesis.

Effects of cyclophosphamide on the secondary palate development in golden Syrian hamster: teratology, morphology, and morphometry.

Cyclophosphamide (CP), when injected in hamster mother between days 9 and 11 of pregnancy, was teratogenic in fetuses. On the basis of a morphological study it was deduced that CP delayed the reorientation of hamster palatal shelves by 16-20 h. In a subsequent experiment, in both control and CP-treated palatal shelves, the numbers of epithelial and mesenchymal cells were counted and cross-sectional area was measured. DNA synthesis, measured by 3H-thymidine incorporation, was used as an index of growth by cell proliferation. The results showed that during the vertical development of palatal shelves, the mesenchymal cells reached their peak number during the initial 24 hours, i.e., at the end of the second peak in DNA synthesis, and remained unchanged thereafter throughout reorientation. The shelf area also showed rapid increase during the initial 24 h followed by a spurt 2 h prior to reorientation. Cyclophosphamide prolonged the acquisition of these features by affecting the mesenchymal cells and consequently delayed the reorientation of the vertical shelves until such time that the number of healthy mesenchymal cells and shelf area were restored to the control values. The data lend further support to the hypothesis that the acquisition of a specific number of cells and shelf volume, during vertical palatal development, may be essential for palatal shelf reorientation.

Vertical development of the secondary palate in hamster embryos following exposure to 6-mercaptopurine.

Cellular aspects of vertical development of the secondary palate were examined in control and 6-mercaptopurine (6MP)-treated hamster embryos. Cross-sectional area of the palatal shelf was measured and the numbers of both epithelial and mesenchymal cells counted. Also, in 6MP-treated palates the damaged mesenchymal cells, characterized by the presence of dense bodies, were counted. DNA synthesis in both control and treated fetuses was measured by 3H-thymidine incorporation. The results indicated that both the shelf area and cell numbers increased with age in control and 6MP-treated palates. However, in controls the mesenchymal cell density and DNA synthesis showed two peaks that were absent following 6MP treatment. Unlike controls, in treated embryos the damage to mesenchymal cells became increasingly pronounced between days 10:00 and 10:12 but subsided by day 11:00 of gestation. It is suggested that a major force in the development of the initial primordia and early vertical development of the palatal shelf may be provided by a spurt of DNA synthesis in the mesenchymal cells resulting in their increased number. After 6MP treatment, depression of DNA synthesis and consequent reduction in the mesenchymal cell number and density followed by cell damage lead to retardation in the vertical development of the palatal shelves.

Gross and cellular analysis of 6-mercaptopurine-induced cleft palate in hamster.

The present study analyzes the morphological, histochemical, and ultrastructural aspects of the pathogenesis of 6-mercaptopurine (6MP)-induced cleft palate in hamster fetuses. Gross and light microscopic observations indicated that 6MP stunts the growth of vertical palatal shelves and thus induces cleft palate. Ultrastructural analysis showed that, in contrast to controls, 6MP-induced alterations were first seen in the mesenchymal cells 24 hr after drug administration. The initial alterations were characterized by swelling of the nuclear membrane. During the next 12 hr, lysosomes were seen first in the mesenchymal cells and then in the cells of the medial edge epithelium (MEE) of the developing palatal primordia. The appearance of lysosomes was temporally abnormal and was interpreted as a sublethal response to 6MP treatment. Subsequently, the nuclear alterations and the lysosomes diminished; and 48 hr after 6MP administration, they were absent from the palatal tissues. Ninety hours after 6MP administration, unlike the controls (in which the palatal shelves were already fused), changes were seen at the epithelial-mesenchymal interface in the developing cleft palatal shelves. These changes were characterized by breakdown of the basal lamina and epithelial-mesenchymal contacts. Eventually, at term, the MEE of the vertical shelf stratified. It was suggested that 6MP affected cytodifferentiation in the palatal tissues during the critical phase of early vertical shelf development and thereby induced cleft palate.

The effects of nitrous oxide on the developing hamster embryos.

Pregnant hamsters were exposed to different concentrations of nitrous oxide during the period of organogenesis. Teratogenic effects were observed in a small but significant number of fetuses. Types of malformations included cleft palate, limb defects, gut herniation, and fetal edema. A dose-effect relationship was not observed. It is not clear from our observations whether the observed effect on the fetuses was due to the excess of nitrous oxide, hypoxia, or a combination of both. Comparison with published literature indicates that further studies on the effects of nitrous oxide in placental animals are needed.

Developmental abnormalities induced by 6-mercaptopurine in the hamster.

Pregnant hamsters were given varying doses of 6-mercaptopurine (6MP) at various times during gestation. The fetuses were examined for both gross and histological malformations which showed that the toxic and teratogenic effects of 6MP were dose and time dependent. The most severe gross malformations induced by 6MP were cleft palate, micrognathia and agnathia, microglossia, short limbs, and gut herniation. Grossly normal appearing fetuses, greated during late gestation, showed malformations at the tissue and cellular level. The effects of 6MP in hamster was compared with other species, and with other growth-supressive agents, and it was deduced that the teratogenicity of 6MP is species and tissue specific. Also, it was recommended that histological observations be made an integral part of the teratological safety analysis.