Effects of methyl mercury on murine fetal amino acid uptake, protein synthesis and palate closure

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Abstract
Methylmercury (MeHg: 5 mg Hg/kg maternal body weight) in 0.13 M NaCl, 0.01 M NaH2PO4‐Na2HPO4, pH 7.4 (PBS) administered to gravid CFW mice on day 12, hour 6 (126) of gestation induced a high incidence of cleft palate in fetuses examined on days 156 (72%), 166 (62%) and 176 (40%). Palate closure (100%) in PBS control animals occurred by 1410. One day post MeHg administration, total fetal protein was decreased 22% while DNA content was unaltered. Protein was maximally decreased (28%) on 146 and, thereafter, returned toward control levels. Alterations in DNA content followed a similar pattern; but the maximal decrease (32%) occurred on 156. The rate of fetal protein synthesis was depressed 5% at 129 and between 20% to 26% from this time to 136 (end of observation). The agreement between the calculated decrease in protein synthesis (19%) and the measured decrease in protein content (22%) suggests that a reduction in protein synthesis is responsible for the decreased fetal protein content. Pacental blood flow and fetal water space, measured with 3H – H2O at 1218, were not affected by MeHg treatment. However, fetal free amino acid concentrations at 1218 were generally decreased (alanine, 23.0%; valine, 9.7%; methionine, 22. 6%; isoleucine, 12.0%; leucine, 18.2%) while uptake of the non‐metabolizable amino acid, 14C‐cycloleucine, was decreased 23%. From this, it is concluded that the growth inhibitory effects of MeHg are related, at least in part, to impaired placental/fetal transfer of amino acids.