Local 42 degrees C hyperthermia improves vascular conductance of the R3230Ac rat mammary adenocarcinoma during sodium nitroprusside infusion

The effect of sodium nitroprusside-induced hypotension on the perfusion of the R3230 adenocarcinoma during local 42 degrees C hyperthermia was studied using a combination of intravital microscopy and laser Doppler flowmetry. Fischer 344 rats were implanted with dorsal skin flap window chambers conta ining the R3230Ac tumor and allocated to three treatment groups (34 degrees C with nitroprusside, 42 degrees C with nitroprusside, and 42 degrees C wi th 0.9% saline). After baseline observation at 34 degrees C, tumors were lo cally heated to 42 degrees C using a water bath and either 0.9% saline or n itroprusside sufficient to reduce blood pressure 20% below pretreatment bas eline was infused. Nitroprusside at 34 degrees C decreased tumor vascular c onductance 40% with no effect on the diameter of arterioles entering the tu mor. The diameter of arterioles entering 42 degrees C heated tumors increas ed 35% independent of blood pressure change. Saline at 42 degrees C had no effect on tumor vascular conductance; however, nitroprusside at 42 degrees C increased tumor vascular conductance 55%. Local 42 degrees C tumor heatin g, combined with a moderate reduction in blood pressure with nitroprusside, overrides the vascular steal effect associated with reduced perfusion pres sure alone and results in improved tumor perfusion. Observations of the eff ect of vasodilator substances on normothermic tumor perfusion cannot be ext rapolated to situations where moderate hyperthermia is used. (C) 2000 by Ra diation Research Society.