AJP - Regulatory, Integrative and Comparative Physiology, Vol 250, Issue 2 235-R239, Copyright © 1986 by American Physiological Society
Fetal renal contribution to amniotic fluid osmolality during maternal hypertonicity
L. L. Woods
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.
