Fetal renal contribution to amniotic fluid osmolality during maternal hypertonicity.
The contribution of fetal urine to the increase in amniotic fluid osmolality during maternal hypertonicity was studied in chronically catheterized sheep of 130-135 days gestation. Nine percent NaCl was injected simultaneously into fetal and maternal veins, followed by a continuous infusion into the maternal vein. Maternal and fetal plasma osmolalities rose by 15 +/- 1 (SE) and 13 +/- 1 mosmol/kg, respectively, and remained constant for 4 h. Fetal urine osmolality rose significantly from 188 +/- 31 to 277 +/- 32 mosmol/kg within 1 h and remained constant thereafter. Fetal urine flow rose transiently, fell to normal within 10 min, and averaged 70% of normal beyond 1 h. Amniotic fluid osmolality rose by 10.8 +/- 2.8 mosmol/kg over 4 h. Following hypertonic injection into three fetuses blocked by the arginine vasopressin antagonist d(CH2)5D-tyr(Et)VAVP, urine osmolality did not change, and amniotic fluid osmolality rose by 2.7 +/- 0.3 mosmol/kg. Thus it appears that the increase in amniotic fluid osmolality during maternal hypertonicity may be due largely to an increased fetal urine osmolality coupled with a decreased flow of fetal urine into the amniotic space, rather than to bulk flow of fluid across the membranes and uterine wall.
D000653:Amniotic Fluid / Q000032:analysis*; D000818:Animals; D001127:Arginine Vasopressin / Q000037:antagonists & inhibitors; D005260:Female; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000196:embryology*; D008431:Maternal-Fetal Exchange; D009994:Osmolar Concentration; D011247:Pregnancy; D012462:Saline Solution, Hypertonic / Q000494:pharmacology*; D012756:Sheep; D012965:Sodium Chloride / Q000494:pharmacology*; D013997:Time Factors
D012462:Saline Solution, Hypertonic; D001127:Arginine Vasopressin; D012965:Sodium Chloride