1-DEAMINO-[8-D-ARGININE] VASOPRESSIN-INDUCED MATERNAL PLASMA HYPOOSMOLALITY INCREASES OVINE AMNIOTIC-FLUID VOLUME

OBJECTIVE: Maternal 1-deamino-[8-D-arginine] vasopressin (a selective antidiuretic agonist) and oral water loading decrease maternal and fet al plasma osmolality and markedly increase fetal urine flow in sheep o ver 24 hours. We hypothesized that a sustained reduction in plasma osm olality would increase the amniotic fluid volume. STUDY DESIGN: Pregna nt sheep (130 +/- days, n = 6) were given oral water loading (2000 mi) and intravenous 1-deamino-[8-D-arginine] vasopressin (20 mu g injecti on followed by 4 mu g/hr) to induce maternal urinary antidiuresis and to maintain a maternal plasma osmolality decrease of approximately 20 mOsm/kg for 48 hours. Fetal plasma osmolality, electrolytes, atrial na triuretic factor, and arginine vasopressin levels, fetal swallowing ac tivity, and fetal urine flow and composition were measured each study day, and amniotic fluid volume was measured by tracer dilution before and at 48 hours of plasma hypoosmolality. RESULTS: In response to 1-de amino-[8-D-arginine] vasopressin and water loading, maternal plasma os molality decreased (298 +/- to 275 +/- 3 mOsm/kg), mirrored by fetal p lasma hypoosmolality (293 +/- 1 to 271 +/- 3 mOsm/kg). Fetal urine osm olality (155 +/- 16 to 117 +/- 10 mOsm/kg) and amniotic fluid osmolali ty significantly decreased (281 +/- 3 to 269 +/- 5 mOsm/kg). Fetal uri ne flow rate significantly increased (0.33 +/- 0.06 to 0.51 +/- 0.04 m l/min), whereas fetal swallowing activity decreased (56 +/- 7 to 33 +/ - 5 swallows per hour). In response to alterations in fetal fluid dyna mics, amniotic fluid volume significantly increased from 493 +/- 80 to 839 +/- 160 mi. CONCLUSION: Chronic maternal 1-deamino-[8-D-arginine] vasopressin-induced plasma hypoosmolality induces a sustained reducti on in fetal swallowing activity and an increase in fetal urine product ion, which results in a marked increase in amniotic fluid volume. Use of maternal 1-deamino-[8-D-arginine] vasopressin and oral fluid loadin g has the potential for manipulation of amniotic fluid volume homeosta sis and may prove useful in the treatment of oligohydramnios.