Steady-state arterial pressure-urinary output relationships during ovine pregnancy.

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 ...