Foetal plasma magnesium levels during maternal hypo- or hypermagnesaemia in ewes.

1. The influence of maternal hypo- or hypermagnesaemia of foetal plasma magnesium levels was studied in pregnant ewes between the 120th and the 145th day of gestation using a permanent catheter inserted in utero into the left aorta of the foetus on the 115th day of gestation. 2. In seven ewes, carrying eleven foetuses, the injection of 1 alpha-hydroxycholecalciferol induced a hypomagnesaemia which lasted 72 h. This had no significant effect on foetal plasma Mg levels. 3. In five ewes, carrying six foetuses, hypermagnesaemia induced by a 2 h magnesium chloride infusion had no significant effect on foetal plasma Mg levels. 4. These results provide evidence that in sheep during the last 20 d of gestation the foetal regulation of plasma Mg is independent of the maternal plasma Mg levels.