Effect of intravertebral angiotensin II on cardiac output and its distribution in conscious dogs.

Intravertebral infusion of angiotensin II (Ang II) increases mean arterial pressure (MAP), but the contribution of cardiac output (CO) and total peripheral resistance (TPR) to this increase is unclear. In the present study, the effects of Ang II infusion on CO and regional blood flow was determined by the microsphere technique in eight conscious, chronically catheterized dogs. Ang II was infused into both vertebral arteries at 0.33 and 1.0 ng/kg/min, and intravenously at 0.66, 2.0 and 5.0 ng/kg/min. Intravertebral infusion of Ang II at 0.33 ng/kg/min increased MAP by increasing CO without changing TPR or peripheral plasma Ang II concentration. MAP also was increased with intravertebral infusion of Ang II at 1.0 ng/kg/min, but this resulted from small increases in both CO and TPR. In contrast, intravenous infusion of Ang II at 2.0 and 5.0 ng/kg/min increased MAP by increasing TPR in association with a decrease in CO. The increase in CO with intravertebral infusion of Ang II at 0.33 ng/kg/min was distributed primarily to the muscles, kidneys, heart, and brain. Intravenous infusion of Ang II at 5.0 ng/kg/min and, to a lesser extent, 2.0 ng/kg/min decreased blood flow to the skin, splanchnic region, and kidneys. These data indicate that the increase in MAP produced by a low intravertebral dose of Ang II results from an increase in CO, which is distributed primarily to the muscle, kidney, heart, and brain. In contrast, the increase in MAP produced by a higher intravertebral dose of Ang II results from increases in CO and TPR. This latter action is apparently due to a peripheral action of Ang II to increase resistance in the skin, splanchnic, and renal circulations.