Differential effects of ornithine on placental lactogen and growth hormone secretion in the pregnant ewe and fetus.

The intravenous infusion of ornithine (0.5-0.9 g/kg) into five fetal sheep of 116-141 days gestation caused no significant change in concentrations of fetal plasma placental lactogen (PL) or GH as determined by specific homologous radioimmunoassays. In contrast, the intravenous infusion of ornithine (0.3-0.5 g/kg) into three of the ewes caused a 144.5 +/- 74.7 (S.E.M.)% increase in maternal plasma PL concentrations and a 255.2 +/- 55.0% increase in maternal GH concentrations. Fetal PL concentrations remained unchanged depsite the large increase in maternal PL concentrations. This study, which indicates a differential effect of ornithine on PL and GH secretion in the mother and fetus, suggests that the factors regulating PL and GH secretion in the mother and fetus are distinct.