Hemodynamic and behavioral effects of angiotensin II in conscious sheep.

Intracerebroventricular (ivt) angiotensin II (ANG II) at 0.4, 2, 10, and 50 ng.kg-1.min-1 increased arterial pressure in conscious sheep in a dose-related manner (26 mmHg, P less than 0.05, at 50 ng.kg-1.min-1). Total peripheral resistance (TPR) and right atrial pressure also increased. Heart rate, stroke volume, and cardiac output did not change. Pressor responses to ivt ANG II were not caused by leakage of ANG II into the periphery, because plasma concentrations of ANG II did not change from control (31 +/- 7 pg/ml) at the highest dose of ANG II infused. In contrast, intravenous (iv) ANG II, 10 and 50 ng.kg-1.min-1, increased arterial pressure 29 and 47 mmHg, respectively (P less than 0.05), and decreased heart rate. ANG II, 10 ng.kg-1.min-1 iv, increased plasma ANG II levels from 36 +/- 6 to 354 +/- 69 pg/ml (P less than 0.05). Intracarotid (ic) ANG II, 10 ng.kg-1.min-1, increased arterial pressure 31 mmHg (P less than 0.05) but did not alter heart rate. ANG II ivt caused a dose-related drinking response, with a positive correlation between the amount of water drunk during ivt ANG II infusion and the increase in arterial pressure. Infusions of ANG II at 50 ng.kg-1.min-1 ivt were associated with decreased plasma osmolality and potassium concentration and increased plasma vasopressin concentration.