The effects of long-term administration of 3H-digoxin to the pregnant ewe upon the cardiovascular hemodynamics of the fetal lamb.

Placental transfer of tritiated digoxin in the ewe and its effect upon the left ventricular output (LVO) of the exteriorized fetal lamb were studied. Seven ewes were given 6 mug per kilogram of body weight of tritiated digoxin daily (20 per cent of total digitalizing dose 0.03 mug per kilogram of body weight) during their entire pregnancies. The fetuses were exteriorized between 130 and 140 days of gestation, and the LVO was determined serially by the dye-dilution technique for one hour. The mean tissue concentrations in millimicrograms per gram for the ewes were: heart, 5.7 plus or minus 1.76; liver, 3.38 plus or minus 1.38, kidney, 01.9 plus or minus 12.3. Corresponding values for the fetuses were: 1.55 plus or minus 1.01, 0.78 plus or minus 0.35, and 2.48 plus or minus 1.18. The mean serum level for the ewe at the end of one hour was 1.65 ng. per milliliter plus or minus 0.48, and that for the fetus was 1.22 plus or minus 0.20. The amniotic fluid contained 1.45 ng. per milliliter plus or minus 0.27. At the end of one hour, the mean LVO of the fetus had decreased by 39 plus or minus 15 per cent of its control value. Although the fetal serum level of tritiated digoxin was similar to that found in the mother and the amniotic fluid contained a significant amount of tritiated digoxin, the fetal tissue concentration of tritiated digoxin was not sufficient to produce any demonstrable inotropic effect.