Hemodynamic Effects of Angiotensin in Normal and Environmentally Stressed Monkeys

Abstract

Simultaneous regional blood flow and resistance measurements were made in 21 organs in 11 supine unanesthetized rhesus monkeys before and during two different doses of intravenously infused angiotensin II or saline. Systemic arterial pressure and total peripheral resistance significantly increased at both infusion rates in the six experimental monkeys, compared with changes in five control monkeys; cardiac output decreased at the high dose level. Among major organs, the kidneys, skin, liver (hepatic artery), and mesentery had reductions in the fraction of cardiac output they received and, thus, the greatst increase in resistance and decrease in blood flow. No organ had a significant increase in its blood flow; however, skeletal muscle and bone were normally perfused due to increases in the fraction of cardiac output they received. Four other monkeys received continuous intravenous angiotensin infusions at initially subpressor rates for periods of 26 to 30 days. There were steady increases of systemic arterial blood pressure due to a rise in total peripheral resistance which reached a plateau in about 5 days. Avoidance schedules or other environmental stresses in these angiotensin-infused monkeys produced much more marked pressor episodes than those which occur in noninfused monkeys. These observations support the hypothesis that small amounts of angiotensin can potentiate sympathetic mediated vasomotor activity.