Vasopressin Decreases Lung Water In Fetal Lambs

Lung liquid volume in fetal lambs decreases before birth, as systemic arterial pressure and plasma protein concentration increase (Bland et al, J Appl Physiol 53:992, 1982). These developments may be the result of hormonal changes that occur late in gestation. Plasma concentrations of vasopressin increase several hours before birth in fetal lambs (Stark et al, Biol Neonate 35: 235, 1979) and intravenous infusion of arginine vasopressin causes reabsorption of fetal lung liquid (Perks & Cassin, Chest 81:63S, 1982). In chronic studies of 9 fetal lambs we found that plasma vasopressin, measured by radioimmunoassay, increased from 2.3± .4 pg/ml before labor to 37.2±9.2 pg/ml late in labor. In lambs killed during labor, there was an inverse relationship between lung water content and plasma vasopressin concentration. To see if this hormone might contribute to the prenatal decrease in fetal lung liquid, we intravenously infused either arginine vasopress in (treated) or isotonic saline (control) for 8 h in 4 sets of twin fetal lambs at 90-95% of term gestation. Plasma vasopressin concentrations in treated lambs were similar to those measured in lambs during labor. Infusion of vasopressin increased systemic arterial pressure by 9±3 torr and plasma protein concentration by 3±1 mg/ml. Extravascular lung water, measured gravimetrically, was significantly less in treated twins than in controls (11.9±1.0 vs 13.8±1.0 g/g dry lung). Thus, vasopressin may contribute to the hemodynamic changes and reduction in lung liquid that occur in lambs before birth.