Effect of sodium nitroprusside-induced hypotension on the blood flow in subcutaneous and intramuscular BT 4An tumors and normal tissues in rats

Abstract

To examine the effect of infusion of the vasodilator sodium nitroprusside (SNP) on the blood flow in normal tissues and BT4An tumors growing subcutaneously or intramuscularly in BD IX rats. Sodium nitroprusside was given as a continuous intravenous infusion to keep the mean arterial pressure stable at 60 mmHg. The cardiac output, organ blood flow, and perfusion of the BT4An tumors were measured by injection of radiolabelled microspheres at control conditions and after 20 min SNP infusion in each animal. Two series of experiments were performed with two anesthetics with different mechanisms of action, Inactin and the midazolam-fentanyl-fluanisone combination (MFF), to secure reliable conclusions. Cardiac output, heart rate, and blood flow to the skeletal muscles, heart, and liver increased during SNP infusion in either anesthetic group. In the kidneys and particularly the skin, decreased blood flow by SNP was observed. When located subcutaneously on the foot, the blood flow in the tumor fell to 23.4% and 21.4% of the control values in the MFF- and Inactin-anesthetized animals, respectively. This was accompanied by a similar fall in the blood flow in the foot (tumor bed) itself. In the intramuscular tumor, the blood flow fell to 24.8% of the control value in the MFF group, whereas the corresponding figure was 36.2% in the Inactin group. In the surrounding muscle (tumor bed) the blood flow increased significantly, most pronounced in the MFF experiment, where it was tripled. The fall in the tumor perfusion by SNP may be exploited therapeutically to increase the tumor temperature during hyperthermia. Predominant heating of the tumor compared to the tumor bed can be expected if the tumor is growing in or near skeletal muscles.