The energy metabolism of RIF-1 tumours following hydralazine.

Phosphorus-31 Magnetic Resonance Spectroscopy (MRS) was used to observe the effect of two doses of the vasodilator hydralazine on the energy status of RIF-1 tumours. An intravenous dose of 5 mg/kg hydralazine reduced the high energy phosphate metabolites PCr and ATP, lowered pHMRS and raised the levels of inorganic phosphate of tumours within 20 min of administering the drug. The levels of high energy metabolites continued to decrease for at least 24 h. Normal muscle spectra obtained up to 1 h after drug administration remained unchanged. An intravenous dose of 0.5 mg/kg hydralazine also reduced NTP/Pi and PCr/Pi levels of tumours up to at least 5 h after drug administration, but the effect was smaller than for the higher dose. Blood flow measurements and measurements of systemic blood pressure demonstrated that 5 mg/kg of hydralazine produced a reduction in both systemic blood pressure and tumour blood flow relative to most normal tissues investigated. It is concluded that the changes in the P-31 MRS spectra of tumours were due to a reduction in tumour vascular perfusion following administration of hydralazine.