Induction of cleft palate in aniline hydrochloride‐treated rats: Possible effect of maternal methemoglobinemic hypoxia

ABSTRACT  Aniline hydrochloride (AH), a methemoglobin formation‐stimulating substance, at a dosage level of 520 mg/kg which does not induce apparent fetal death, was injected subcutaneously into pregnant rats once on day 14, 15 or 16 of gestation in order to assess the stage specificity of cleft palate induction. Also, doses of 260, 390, 520 and 650 mg/kg were administered to pregnant rats on day 15 of gestation, and the dose‐response relationships with respect to fetal cleft palate and maternal methemo‐globinemia induction were studied. In the stage‐specificity study, paleness, decreased body weight gain and elevated methemoglobin concentration were noted in the dams treated with AH. Upon fetal examinations, although reduced body weight was noted in all AH‐treated groups, cleft palate was observed only in fetuses from those dams treated on day 15 of gestation. In the dose‐dependency study, AH induced maternal methemoglobinemia, decreased fetal body weight and increased the incidence of cleft palate dose dependently when administered at dosage levels of 260, 390, 520 and 650 mg/kg on day 15 of gestation. Additionally, administration of methylene blue, a methemoglobinemia‐preventing substance, to the AH‐treated dams ameliorated maternal methemoglobinemia and reduced the incidence of fetal cleft palate. In summation, it is considered that AH stage‐specifically induces cleft palate in rats and that cleft palate is caused not by a direct teratogenic effect of AH but by maternal hypoxia due to methemoglobinemia.