Effects of Intravenous Infusion of Dopamine on Tumor Blood Flow in Rat Subcutis

To determine the effects of intravenous administration of dopamine hydrochloride (DA) on tumor blood flow (TBF), we measured the blood flow of normal subcutaneous tissue and subcutaneous tumor (LY‐80, a variant of Yoshida sarcoma) in enflurane‐anesthetized male Donryu rats using a hydrogen clearance method. Measurements were made before and during intravenous infusion of DA at a rate of 5μg/kg/min, while recording the mean arterial blood pressure of the rats. Under mild hypertension induced by DA, the blood flow of normal subcutis decreased and TBF increased significantly. SCH‐23390, an antagonist of the DA(1) receptor, inhibited the enhancement of TBF by DA; while domperidone, an antagonist of the DA(2) receptor, did not modify the effects of DA. In experimental chemotherapy against the tumor using adriamycin (ADM) 5 mg/kg i.v., only the combination of DA and ADM significantly inhibited the tumor growth. Moreover, DA reduced the weight loss caused by ADM. These results indicate that DA could have a role in increasing TBF and possibly enhance drug delivery to tumors. Moreover, it appears that the DA(1) receptor contributes, at least in part, to the enhanced blood flow in rat subcutaneous tumor following DA administration.