LOWERING PH INCREASES EMBRYONIC SENSITIVITY TO FORMATE IN WHOLE-EMBRYO CULTURE

The effects of formate exposure on mammalian embryo development were i nvestigated using the rat whole embryo culture system as a model. Day 9.5 (presomite) rat embryos were explanted and cultured for 48 hr in r otating bottles containing rat serum with 0, 0.2, 0.4, 0.8, 1.2 or 1.6 mg sodium formate/ml culture medium at pH 8.13, 7.75, 7.00, 6.50 or 6 .00 to determine whether the pH of the culture medium affects the in v itro developmental toxicity of formate. Several parameters of embryoni c development decreased in the presence of decreasing pH, suggesting t hat altered pH alone could have a negative impact on embryo developmen t. Exposure to 1.6 mg formate/ml affected protein concentration, somit e number (SN), head length (HL), developmental score (DS), crown-rump length (CRL) and yolk-sac diameter of embryos at all pH levels. Format e became more toxic with decreasing pH of the culture media. There was an apparent pa-dependent increase in embryolethality at 1.6 mg format e/ml and 100% lethality at pH 6.00. The 1.2-mg/ml formate concentratio n affected DS, CR, HL and protein content at the pH 7.75 level whereas 0.8 mg formate/ml resulted in reduced DS, HL, CR, SN and protein cont ent at pH levels of 7.00 and lower. At pH 6.5, embryos that were not e xposed to formate were not significantly different from the other cont rol groups except in reduced CR but at this pH, all exposure levels of formate resulted in microcephaly and reduction in embryonic protein a s well as reduced CR. These data demonstrate that sensitivity to forma te-induced embryo toxicity and dysmorphogenesis in whole embryo cultur e is increased in the presence of lower pH.