AJP - Regulatory, Integrative and Comparative Physiology, Vol 258, Issue 2 469-R475, Copyright © 1990 by American Physiological Society
Temporal relationships among fetal urine flow, ANF, and AVP responses to hypertonic infusions
L. K. Miner, R. A. Brace and C. Y. Cheung
Department of Reproductive Medicine, University of California, San Diego, La Jolla 92093.
The fetal urine flow response to acute increases in osmolality may be
mediated by changes in the plasma concentrations of atrial natriuretic
factor (ANF), arginine vasopressin (AVP), and/or angiotensin II (ANG II).
To explore this, hypertonic NaCl or mannitol was infused intravascularly
over 10 min into chronically catheterized fetal sheep and their mothers
simultaneously, followed by a 2-h maternal infusion at 1-2 ml/min to
maintain the elevated osmolality. Fetal osmolality rose by 16 mosmol/kgH2O
during 13% mannitol and 2.5% NaCl infusions and by 57 mosmol/kgH2O during
7% NaCl infusions. Large increases in fetal urine flow occurred in the
three groups with peak flows (average of 304%, P less than 10(-6)) at 0-4
min after the end of the infusion. Flow declined to preinfusion values in
all groups at 30-40 min. These changes in urine flow occurred in parallel
with a rise (to 223%, P less than 10(-6)) and fall in plasma ANF
concentrations. One hour after the infusions, urine flow declined to 50% of
control concomitant with elevations in plasma AVP (to 414%, P less than
10(-6)), whereas plasma ANG II concentration did not change. Thus the
initial increase in fetal urine flow in response to acute hypertonic
infusions is temporally related to a rise in fetal plasma ANF, whereas the
subsequent fall in urine flow is temporally related to a fall in plasma ANF
and a simultaneous rise in AVP concentration. This suggests that ANF may
contribute to the acute urine flow increase after hypertonic infusion,
whereas AVP appears to be more important for the long-term regulation of
fetal urine flow.
