Differential response of ovine placental lactogen levels in maternal and fetal circulations following single umbilical artery ligation in fetal sheep.

We investigated circulating maternal and fetal serum concentrations of ovine placental lactogen (oPL) following single umbilical artery ligation (SUAL) at 108 to 114 days' gestation. Ovine placental lactogen was isolated and purified from placental cotyledons, and a radioimmunoassay developed using previously described methods. Intrauterine growth retardation (IUGR) was manifest as increasing fetal brain-to-liver weight ratio with increasing duration of survival following SUAL. During the first five to seven days following SUAL, circulating oPL levels in ewes with SUAL fetuses were significantly reduced when compared with levels in ewes with control fetuses. In contrast, oPL levels in SUAL fetuses were significantly increased above levels in control fetuses for the first five to seven days following surgery. Fetal ovine growth hormone levels were elevated in SUAL fetuses, while ovine prolactin levels were similar in the two groups. IUGR was associated with mild fetal acidosis and fetal plasma CAT levels which were similar in SUAL and control fetuses. No correlation was found between fetal pH or CAT and fetal oPL levels. These findings are consistent with the view that circulating levels of oPL in the mother are related to the mass of functioning trophoblast. Elevated fetal oPL levels following SUAL may result from acute placental ischaemia with alterations in placental lactogen secretion at the maternofetal interface.