DISTRIBUTION OF METHIONINE AND ITS METABOLITES IN THE PREGNANT EWE AND FETUS FOLLOWING INTRAVENOUS OR ABOMASAL INJECTION OF 35S-METHIONINE INTO THE EWE

Abstract

The placental transfer of 35S-Methionine was studied in the chronically cannulated ovine fetus following intravenous or intra-abomasal administration of varying methionine loads into the ewe. Transport of methionine across the ovine placenta was related to duration and degree of elevation of maternal plasma methionine concentrations. Placental regulation of transport involved buffering of minor fluctuations in maternal blood methionine level and limitation of the rate of transfer from ewe to fetus. Fetal ability to clear methionine from plasma was limited relative to maternal ability. Patterns of accumulation of metabolites in maternal and fetal blood, and in amniotic fluid suggested a reduced capacity for methionine metabolism by the fetus. Maintenance of elevated maternal plasma methionine concentrations increased fetal fluid concentrations to extremely high levels. The data reconcile previous differences observed in methionine transfer across the placenta when injected at different concentrations. Key words: Methionine, 35S, ewe, fetus, placental transfer