Renin response and angiotensinogen control during graded hemorrhage and shock in the dog

Hemorrhage and hemorrhagic hypotension have been shown to be potent stimulators of renin release. However, the relationship between angiotensinogen consumption and angiotensinogen production has yet to be completely defined during this type of circulatory stress. Peripheral renin activity increased progressively as the blood pressure was decreased stepwise by hemorrhage to 50 mmHg and remained elevated throughout the shock phase of the experiment. Angiotensinogen did not change from control (809 ng/ml) throughout hemorrhabic hypotension and shock. During hemorrhagic hypotension, with the infusion of the angiotensin antagonist, [1-sarcosine, 8-alanine]angiotensin II, angiotensinogen concentration fell progressively from 693 to 208 ng/ml at 50 mmHg. Intravenous angiotensin II infused continuously after the mean blood pressure reached 50 mmHg significantly elevated plasma angiotensinogen concentration. In conclusion, during hemorrhagic hypotension and shock, the kidney and the liver appeared capable of maintaining elevated plasma renin activity and adequate plasma renin substrate, angiotensinogen, respectively. The mechanism responsible for the maintenance of plasma angiotensinogen is suggested to involve a positive-feedback effect of angiotensin II on the liver.