Blood flow alteration induced by saralasin or sodium nitroprusside in rats

The radioactive microsphere technique was used to investigate the distribution of blood flow during halothane anesthesia when either sodium nitroprusside (SNP) or saralasin, a competitive inhibitor of angiotensin II, was infused. Seventeen fasted male Wistar rats were anesthetized with halothane and received either saralasin (n = 6) or SNP (n = 11) to decrease mean arterial pressure 20 torr. Cardiac output was unchanged with SNP, but blood flow decreased 23 per cent to the brain, and 25 per cent to the kidney, while splanchnic flow increased 19 per cent (P less than .05). There were 37 per cent less microspheres present in the lung after drug treatment. Saralasin did not alter cardiac output or flow to other organs but did cause a 49 per cent decrease in the number of microspheres found in the lung after drug treatment. An additional group of rats first received SNP, and then saralasin. This combination was not well tolerated, resulting in lethal hypotension and a mortality of 60 per cent. In the thirteen animals which were able to complete the protocol, increases in blood flow to the heart, kidney and splanchnic circulation were seen while brain flow decreased (P less than .05). The number of microspheres in the lung also decreased after combined therapy. These studies demonstrate the differential effects of SNP and saralasin in lowering blood pressure. The use of combined drug treatment, when tolerated, may improve organ perfusion.