Hypoxia and the Edema Syndrome: elucidation of a mechanism of teratogenesis.

The elucidation of mechanisms and pathogenesis of birth defects is exceedingly complex. Consequently, there are few examples where the etiology of birth defects caused by a specific agent has been well described. One such example is the "Edema Syndrome" first described by Casimer Grabowski in the 1960s as a mechanism of hypoxia-induced malformations in the chick embryo. The Edema Syndrome comprised a series of events in the embryo starting with osmotic imbalances followed by edema, distention, blisters, hematomas, and hemorrhage in or near developing structures. Malformation or deformation of structures resulted from mechanical disruption or loss of blood supply. A similar etiology has since been described by others in a variety of laboratory mammals following treatment with drugs including epinephrine, hydroxyurea, cocaine, phenytoin, and potassium channel-blocking drugs. Free radical excess following transient hypoxia may be a common factor in all of these insults. Vascular disruption is also associated with a number of birth defects in humans, including limb and digit reduction defects and urogenital defects.

Hematomas and limb skeletal malformations in chicken embryos following exposure to 5-fluoro-2-deoxyuridine.

Vascular injury or interruption may play a role in vertebrate limb teratogenesis. Since 5-fluoro-2'-deoxyuridine (FdU) can cause vascular injury in the murine limb and skull prior to the appearance of skeletal malformations in these structures, we studied the effects of this chemical on skeletal development in the chick embryo and noted any vascular injury. The yolk sacs of day three chick embryos (Hamburger and Hamilton states 17-19) were injected with solutions of vary concentrations of FdU in saline. The embryos developed until the 10th day of incubation when they were fixed for study. Uninjected, saline injected, and sham injected control embryos were similarly fixed. Upon gross inspection, frequent diffuse and saccular hematomas, as well as fluid-filled blisters, were noted in the limbs of embryos treated with FdU. After the embryos were fixed and cleared, and the skeletons stained, significant skeletal malformations were observed in these limbs. Bony elements of both the upper and lower limbs were affected in at least some of the embryos. The combination of FdU-induced hematomas and blisters with associated skeletal malformations in the same regions of some embryos suggests a relationship between these phenomena.

Effects of sodium valproate and oxygen on the CD-1 mouse fetus.

This study reports the effects of valproic acid (VA) on the CD-1 mouse fetus when the drug is administered continuously via osmotic minipumps at human therapeutic drug plasma levels. Two VA-filled Alzet osmotic minipumps were implanted subcutaneously on gestation day 5 for continuous exposure of a total daily dosage of 850 mg/kg on gestation days 5-12. Dams were then exposed continuously to either normoxic (21% oxygen), hyperoxic (50% oxygen), or hypoxic (12% oxygen) controlled environments during gestation days 5-12, in order to determine if hyperoxic maternal conditions offered a protective environment for the fetus, and conversely, if hypoxia exacerbated teratogenicity. Dams were sacrificed on gestation day 18, and litter and fetal data were collected. It was determined in separate groups under normoxic conditions that the osmotic minipump system maintained VA plasma levels corresponding to human therapeutic levels. Sodium valproate was found to induce developmental toxicity in the CD-1 mouse fetus at human therapeutic drug plasma levels. Fetal weights were reduced, and the number of resorptions, deaths, and hematomas was increased. While hypoxia exacerbated the toxic effect on the fetus, hyperoxia failed to ameliorate the outcome.

Pathogenesis of limb and facial malformations induced by pyrimethamine in the rat.

The temporal sequence of morphological events resulting in limb and face malformations was studied in pyrimethamine (PY) treated female rats, 30 mg/kg of PY in a 10 ml/kg suspension of 0.9% NaCl were administered i.p. on days 12, 13 and 14 of gestation. Controls received only 0.9% NaCl solution. The females were killed at different stages of gestation (between 14 and 21 days). Early PY treated embryos showed mainly haematomas in the extremities and the mandibulo-maxillary areas. During the course of gestation, fewer haematomas and more malformations were observed. At term, malformations were observed in the same localisations where haematomas were previously seen.

Sonography of umbilical cord hematoma following genetic amniocentesis.

A case of umbilical cord hematoma, following genetic amniocentesis, is reported. Spontaneous resorption of the hematoma was observed at sonography. A normal infant was born vaginally at term.

Blebs and hematomas in the lips of CL/Fr and A/J mice.

Newborn-CL/Fr mice have +/- 20% frequency of cleft lip with or without cleft palate (CLP) depending on environment. However, examination of early fetal development from days 12 to 15 disclosed an increased number of hematomas or fluid-filled blebs in the regions of maxillary process fusion. The earliest stages do not appear to involve the blood supply directly but separate the epithelium from underlying mesenchyme by clear blebs. Similar defects were found in untreated A/J mice. These findings suggest that osmotic and hemodynamic abnormalities may be part of the mechanism of cleft lip formation in these related strains and that these defects may result from a biochemical defect of the connective tissue matrix in regions of process fusion.