DEVELOPMENTAL PHASE SPECIFICITY AND DOSE-RESPONSE EFFECTS OF 2-METHOXYETHANOL IN RATS

Methoxyethanol (ME) produces embryotoxic effects in rodents, rabbits, and nonhuman primates. Mechanistic evaluations of ME dysmorphogenesis have focused mainly on developmental insults and chemical disposition in the mouse. These assessments in mice were based on developmental ph ase specificity (DPS) and dose-response relationship (DRR) of ME. DPS and DRR indicated treatments for selectively inducing defects to study ME disposition and expressed dysmorphogenesis. This study was conduct ed to establish DPS and DRR of ME in the rat. DPS was determined by in jecting 500 mg ME/kg (6.6 mmol/kg) into the tail vein on Gestational D ay (gd; sperm-positive day = gd 0) 10, 11, 12, 13, 14, or 15 (n = 6 da ms/gd; saline controls on gd 12). On gd 20, embryolethality incidence was 100% after gd 10 dosing; at gd 11 through 15, it was 50, 32, 15, 2 , and 5%, respectively (control, 2%). Incidences of external defects i n live fetuses exposed on gd 11-15 were 97, 98, 100, 44, and 0% and th ose of viscera were 100, 62, 44, 10, and 0%, respectively. The predomi nant anomalies observed were ectrodactyly and renal agenesis. DRR was determined on gd 13, when live embryos/litter and external malformatio ns (ectro-and syndactyly, micromelia) were maximal. Dams (n = 8/dose g roup) were injected intravenously with 0, 100, 250, 350, or 500 mg ME/ kg. On gd 20, fetal defect rates were 0, 0, 82.5, 83.0, and 100% at th ese concentrations, respectively. Based on these studies, appropriate ME doses, times of maternal exposure, and critical phases of developme nt in the rat model are available for reproducing selective defects to investigate biochemical and pharmacokinetic determinants underlying t heir expression. (C) 1996 Society of Toxicology