Central actions of circulating angiotensin II on the sympathetic nervous system and blood pressure control

The effects of intravertebral artery infusions of [Sar1, Ile8] and [Sar1, Thr8] angiotensin II on the central nervous system were studied in furosemide-treated dogs anesthetized with alpha-chloralose. Acute administration of furosemide led to a significant increase in plasma renin activity, plasma noradrenaline levels and heart rate, and also to a slight rise of blood pressure. In the furosemide-treated dogs, intravertebral artery infusion of either angiotensin II antagonist (250 ng/Kg/min, for 30 min) suppressed the furosemide-induced increases in plasma noradrenaline, heart rate and arterial blood pressure. The effects of [Sar1, Thr8] angiotensin II on the last two parameters were more pronounced than those of [Sar1, Ile8] angiotensin II. Intravenous infusion of the same dose of each antagonist had little influence on the furosemide-induced increases in arterial blood pressure, heart rate and plasma noradrenaline levels. These results suggest that the central actions of angiotensin II contribute to the regulation of blood pressure through the sympathetic nervous system.