Effects of several vasoactive drugs on the vascular resistance of MT-W9B tumors in W/Fu rats.

These experiments were designed to study the effects of vasoactive drugs on normal and malignant tissue in W/Fu rats. The increase in resistance to tumor blood flow elicited by a bolus injection of 10 microgram of norepinephrine was greater than that elicited in the surrounding mammary gland tissue. A 10-fold increase in the resistance to tumor blood flow was sustained for 30 min by the infusion of norepinephrine at the rate of 1.39 microgram/min, whereas a smaller initial increase in mammary gland vascular resistance decreased with time. In contrast, the increase in resistance to tumor blood flow caused by a bolus injection of angiotensin II was less than that observed in the mammary gland tissue. A 20-fold increase in mammary gland vascular resistance could be maintained for at least 5 min by infusion of angiotensin II at the rate of 1.39 microgram/min. In comparison, such treatment caused only a 3-fold increase in the resistance to tumor blood flow. A bolus injection of 1 microgram of isoproterenol decreased the vascular resistance in all normal tissues studied, but the resistance to blood flow in the tumor remained unchanged. The results of these experiments indicate that there may be methods whereby the tumor blood flow can be manipulated for therapeutic purposes and to assist radiographic visualization of tumors.