Intraamniotic deamino(D-Arg⁸)-vasopressin: Prolonged effects on ovine fetal urine flow and swallowing

OBJECTIVE: Fetal urine is the main source of amniotic fluid, and alterations in urine production have an impact on amniotic fluid dynamics. Intraamniotic arginine vasopressin is absorbed into fetal plasma, but fetal antidiuretic responses may be obscured by vasoconstrictor (V₁ receptor) actions of arginine vasopressin. We determined the effects of intraamniotic administration of a specific V₂ receptor agonist, deamino(D-Arg⁸)- vasopressin, on fetal plasma arginine vasopressin immunoreactivity, fetal urine output, and swallowing. STUDY DESIGN: Six chronically prepared pregnant ewes (129 ± 1 days' gestation) received a single deamino(D-Arg⁸) (50 μg injection into the amniotic fluid with subsequent measurement of fetal plasma arginine vasopressin immunoreactivity, fetal urine flow and osmolality, and fetal swallowing. RESULTS: Within 30 minutes of deamino(D-Arg⁸)-vasopressin administration, fetal plasma arginine vasopressin immunoreactivity (4.5 ± 0.5 to 76.4 ± 21.9 pg/ml) and urine osmolality (135 ± 13 to 285 ± 43 mOsm/kg H₂O) significantly increased and urine flow decreased (0.18 ± 0.01 to 0.05 ± 0.01 ml/kg per minute). After 48 hours urine flow remained reduced (0.08 ± 0.03 ml/kg per minute) and osmolality remained elevated (399 ± 18 mOsm/kg H₂O). There were no changes in fetal swallowing, systolic (64 ± 3 mm Hg) or diastolic (42 ± 3 mm Hg) blood pressure, or heart rate (169 ± 6 beats/min). CONCLUSION: Intraamniotic deamino(D-Arg⁸)-vasopressin administration evokes persistent fetal antidiuresis in the absence of arginine vasopressin-induced fetal cardiovascular effects or changes in fetal swallowed volume, indicating its suitability as a potential therapeutic agent in amniotic fluid volume disorders such as polyhydramnios.