Cardiovascular malformations associated with maternal hypoxia due to methemoglobinemia in aniline hydrochloride‐treated rats

Abstract

ABSTRACT  Aniline hydrochloride (AH), a methemoglobin‐formation stimulating substance, at a dosage level that does not induce apparent fetal death was injected subcutaneously into pregnant rats once a day on days 6–8, 9–11, 12–14 or 15–17 of gestation in order to assess its ability to stage‐specifically produce cardiovascular malformations. In addition, AH at dosage levels of 195, 260, 325 and 395 rag/kg was injected into pregnant rats subcutaneously once a day on days 12–14 of gestation, and the dose‐dependent induction of ventricular septal defect (VSD) in relation to maternal methemoglobinemia was studied. In the stage‐specificity study, paleness, decreased body weight gain and elevated methemoglobin concentration were noted in the dams. Upon fetal examination, reduced body weight was noted in all AH‐treated groups. AH induced cardiovascular malformations, mainly VSD, which was most frequently observed in the day 12–14 group and also observed in the day 15–17 group. Abnormal branching of subclavian, pulmonary and vertebral arteries were most frequently observed in the day 9–11 group. In the dose‐dependency study, AH induced maternal methemoglobinemia, decreased fetal body weight and increased the incidence of VSD dose dependency. Additionally, administration of methylene blue, a methemoglobinemia‐preventing substance, to the AH‐treated dams ameliorated maternal methemoglobinemia and reduced the incidence of fetal VSD. From these results, it is considered that AH stage‐specifically induces cardiovascular defects, mainly VSD, in rats and that VSD is induced not by a direct teratogenic effect of AH but by maternal hypoxia due to methemoglobinemia.