Ovine fetal adaptations to chronically reduced urine flow:
preservation of amniotic fluid volume.
Mann, Stephanie E., Mark J. M. Nijland, and Michael G. Ross.
Perinatal Research Laboratories, Department of Obstetrics and
Gynecology, University of California Los Angeles School of Medicine,
Harbor-UCLA Medical Center, 1124 W Carson Street, Torrance, CA
90502
APStracts 3:0363A, 1996.
Adequate amniotic fluid (AF) volume is maintained by a balance of
fetal fluid production (lung liquid and urine) and resorption
(swallowing and intramembranous flow). Because fetal urine is the
principle source of AF, alterations in urine flow and composition
directly impact AF dynamics. Intraamniotic DDAVP (desamino[D-Arg8]
-vasopressin) is rapidly absorbed into fetal plasma and induces a
marked fetal urinary antidiuresis. To examine the effect of intra
-amniotic DDAVP induced fetal urinary responses on AF volume and
composition, six chronically prepared ewes with singleton fetuses
(128+/-2 days gestation) were studied for 72 h following a single
intra-amniotic DDAVP (50 [mu]g) injection. After DDAVP, fetal urine
osmolality significantly increased at 2 h (157+/-13 to 253+/-21
mOsm/kg), and remained elevated at 72 h (400+/-13 mOsm/kg). Urinary
sodium (33.0+/-4.5 to 117.2+/-9.7mEq/l) and chloride (26.0+/-2.8 to
92.4+/-8.1 mEq/l) concentrations similarly increased. AF osmolality
increased (285+/-3 to 299+/-4 mOsm/kg), though there was no change in
fetal plasma osmolality (294+/-2 mOsm/kg). Despite a 50% reduction in
fetal urine flow (0.12+/-0.03 to 0.05+/-0.02 ml/kg/min at 2 h and
0.06+/-0.01 ml/kg/min after 72 h), AF volume did not change (693+/
-226 to 679+/-214 ml). There were no changes in fetal arterial blood
pressures, pH, PCO2, or PO 2 following DDAVP. Conclusions: (1) Intra
-amniotic DDAVP injection induces a prolonged decrease in fetal urine
flow, and increases in urine and AF osmolalities. (2) Despite
decreased urine flow, AF volume does not change. We speculate that,
in response to DDAVP-induced fetal oliguria, reversed intramembranous
flow (from isotonic fetal plasma to hypertonic AF) preserves AF
volume.
Received 30 October 1995; accepted in final form 24 July 1996.
APS Manuscript Number A1148-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 21 August 1996