The embryotoxicity of cyclophosphamide in rabbits during the histiotrophic phase of nutrition.

After iv injection of cyclophosphamide (CP; 80 mg/kg) and dechlor-CP (60 mg/kg) on the 9th day of gestation (histiotrophic phase of nutrition) in rabbits, the concentrations of activated CP and activated dechlor-CP were determined fluorometrically in the maternal blood and in the yolk sac fluid. Activated CP and dechlor-CP could be measured in the maternal blood but not in the yolk sac fluid. This holds true for both the free as well as the protein bound form. During the histiotrophic phase of nutrition on the 9th day of gestation, the yolk sac wall seems to be a barrier for activated CP and dechlor-CP. This phenomenon has to be traced back on the oxazaphosphorinring activated in position C4 and not on the alkylating activity. Therefore, a direct effect of activated CP can be excluded as the main reason for the embryotoxicity of CP. Consequently, the effects of iv-injected CP on the entoderm of the visceral layer of the yolk sac placenta were investigated. Three, 6, 12, and 24 hours after CP injection, the maternal animals were laparotomized and the entoderm of the visceral layer of the yolk sac placenta in the mesometral parts of the blastoderms were prepared for electron microscopy. Like in the control group, 3 hours after CP injection no differences are found. Six hours after CP injection, a relatively flat cell-type can be observed, which is probably based on the reduced absorptive capability of the entoderm. Twelve hours after CP injection the entoderm cells are nearly uniformly of the columnar type; this is interpreted as a restored absorptive activity. Twenty-four hours after CP injection the columnar form of the entoderm cells and the reduced pinocytotic activity are interpreted as a state of secretion. During the histiotrophic phase of nutrition (9th day of gestation in rabbits), CP-induced inhibition of the absorptive activity of the entoderm cells might lead to a quantitatively and/or qualitatively changed nutrition of the developing embryo. This changed nutrition may be the source of the embryotoxic effects of CP.