Deterioration of metabolic coronary regulation in hemorrhagic shock. Role of hypoxia and the renin-angiotensin system.

The effect of hypoxia and the renin-angiotensin system on metabolic coronary regulation in hemorrhagic shock was studied in 22 anesthetized open-chest dogs. Left circumflex coronary blood flow was measured with an electromagnetic flowmeter. Dogs were ventilated with room air (n = 8) or 100% oxygen (n = 7). A third group of dogs was ventilated with room air and bilaterally nephrectomized 5 h prior to starting the experimental protocol (n = 7). After control data had been obtained, dogs were bled from the femoral arteries into a pressurized reservoir which maintained blood pressure at 45 +/- 1 mmHg. The angiotensin II receptor blocker, saralasin, was then infused i.v. (0.1, 1.0, 10.0 micrograms/kg per min). Coronary blood flow was reduced by hemorrhage, and no significant difference existed in coronary flow during hemorrhage among the three groups. Coronary sinus oxygen saturation was diminished in control animals during hemorrhage from 26% +/- 1% to 17% +/- 1% (P less than 0.05) but normal in 100% oxygen ventilated animals (30% +/- 3%) and in nephrectomized dogs (34% +/- 4%). Coronary oxygen extraction was reduced by saralasin in intact but not in nephrectomized dogs. In six additional experiments, in which blood pressure was not artificially held constant during saralasin infusion, saralasin still significantly improved coronary sinus oxygen saturation and thus reduced coronary oxygen extraction. The data suggest that both hypoxia and the renin-angiotensin system participate in the restriction of metabolic coronary regulation in hemorrhagic shock.