A selective reduction in tumour blood flow (TBF) could enhance the effects of hyperthermia treatment and of drugs toxic to hypoxic cells. Vasodilator-induced changes in TBF were monitored in transplanted rat fibrosarcomas by non-invasively measuring the uptake of D2O using 2H nuclear magnetic resonance spectroscopy. Hydralazine (1 or 5 mg kg-1) caused a large (45% reduction in mean arterial blood pressure (MABP) and a 40-60% reduction in TBF. Low-dose hydralazine (0.1 mg kg-1) caused a 20% reduction in MABP but no significant change in TBF. The doses of prazosin (1 mg kg-1) and calcitonin-gene related peptide (CGRP, 1 nmol kg-1) which caused a 20% reduction in MABP led to a 50-60% reduction in TBF. These results demonstrate the advantage of prazosin and CGRP over hydralazine for the reduction of TBF despite a small hypotensive effect. CGRP may be the most suitable of these agents for clinical use because of its short physiological half-life.
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