AJP - Regulatory, Integrative and Comparative Physiology, Vol 263, Issue 5 1141-R1146, Copyright © 1992 by American Physiological Society
Steady-state arterial pressure-urinary output relationships during ovine pregnancy
E. W. Quillen Jr and B. S. Nuwayhid
Department of Obstetrics and Gynecology, McGill University, Montreal, Quebec, Canada.
To determine the effects of long-term changes in sodium intake on mean
arterial pressure (MAP) regulation during pregnancy, nonpregnant (n = 16)
and 110- to 140-day pregnant (n = 13) ewes received total daily sodium
intakes of 10, 30, 100, 400, and 1,200 mmol for 7 days. The sheep were
housed in metabolism cages and MAP was monitored 24 h/day. Urinary sodium
excretion (UNaV) followed changes in sodium intake, with steady-state
levels being achieved with similar degrees of rapidity (2-3 days) in
nonpregnant and pregnant sheep. At 10 mmol/day sodium intake, MAP was lower
(79 +/- 1 vs. 82 +/- 2 mmHg; P < 0.01) and water intake (2,275 +/- 494
vs. 3,286 +/- 725 ml/day; P < 0.001) and 24-h urine volume (1,454 +/-
279 vs. 2,299 +/- 496 ml/day; P < 0.01) were greater in pregnant sheep.
All of these variables exhibited direct relationships with increases in
sodium intake. Plasma angiotensin II (pANG II) was increased in pregnancy
(10.6 +/- 1.6 vs. 24.5 +/- 6.3 pg/ml; P < 0.001) at 10 mmol/day.
Elevation of sodium intake suppressed pANG II to minimal levels in
nonpregnant sheep, but to only 25% of the control level in pregnant sheep.
During pregnancy, the renal function curve representing the steady-state
MAP-UNaV relationship was shifted to lower MAP setpoint, but the sodium
sensitivity of MAP was unchanged. Also, the inverse relationship of sodium
intake and pANG II was blunted, suggesting a reduced role for ANG II in the
maintenance of renal function during pregnancy.
