Indirect hypertensive actions of long-term intracarotid angiotensin II infusion during ovine pregnancy.

Angiotensin II (AngII) influences the regulation of mean arterial pressure (MAP) through numerous mechanisms, including an action of circulating AngII on the brain to alter autonomic activity. We have obtained evidence that the relative importance of this effect is increased during pregnancy. Consequently, these studies were undertaken to assess the effects of bilateral infusion of AngII (0.35 ng.kg-1.min-1.artery-1) into the internal carotid arteries (ica) of sheep for 13 days. Six non-pregnant (NP) and six 105- to 125-day pregnant (PG) ewes were maintained in large metabolism cages, where MAP was continuously monitored. By day 10 of ica AngII infusion in NP ewes, MAP was increased from 83.9 +/- 1.6 to 92.9 +/- 2.8 mmHg (1 mmHg = 133.3 Pa) (p = 0.001). Twenty-four hour urine volume (UV, 2664 +/- 341 to 1583 +/- 228 mL; p = 0.005) and sodium excretion (UNaV, 190 +/- 5 to 113 +/- 19 mmol/day; p = 0.005) were decreased. 51Cr-tagged blood volume (BV) was increased on day 13 (3643 +/- 187 to 4379 +/- 446 mL; p = 0.05). In contrast, by only day 6 of ica AngII infusion in PG ewes, MAP increased from 79.1 +/- 1.9 to 84.1 +/- 1.4 mmHg (p = 0.03) in association with a BV expansion from 3999 +/- 274 to 4207 +/- 275 mL. These changes were preceded by decreases in UV (2813 +/- 413 to 2198 +/- 362 mL; p = 0.01) and UNaV (190 +/- 15 to 118 +/- 26 mmol/day; p = 0.01). By day 13, MAP had plateaued at 93.0 +/- 1.2 mmHg.(ABSTRACT TRUNCATED AT 250 WORDS)