Abstract
Using 31P NMR spectroscopy, changes in tumour metabolic status were studied in a transplanted rat fibrosarcoma following the administration of vasodilators. Mean Arterial Blood Pressure (MABP) was monitored simultaneously. Two vasodilators were studied, prazosin and CGRP, which altered the NMR parameters Pi/sigma P, beta NTP,Pi, PCr/Pi and PME/Pi in a dose dependent manner. There was a good correlation between the various NMR parameters; for analysis, Pi/sigma P was used for convenience. With increasing doses of vasodilator, Pi/sigma P increased and the MABP decreased. Reduction in pHNMR showed a correlation with decreasing MABP following the administration of prazosin but not after CGRP. Both prazosin and CGRP produced changes in 31P NMR spectra consistent with a reduction in tumour blood flow. The results for prazosin and CGRP were comparable and showed a 15-20% increase in Pi/sigma P for a 20% reduction in MABP. These results were compared with those from hydralazine. With hydralazine an acceptable reduction in blood pressure (up to approximately 25%) has little effect and may even alter NMR parameters consistent with an increase in blood flow, a reduction of approximately 40% is required for a significant decrease in flow. Both prazosin and CGRP are shown to be far more effective than hydralazine in causing tumour hypoxia at a clinically acceptable reduction in blood pressure. CGRP may be the more suitable for clinical use because of its short half life, its capability to achieve controlled hypotension and the relatively few side effects associated with its use.
Highlights
A typical 31P NMR spectrum from a tumour is shown in Figure la together with sequential spectra following an intravenous bolus injection of 600 pmol Calcitonin gene-related peptide (CGRP)
The principal change in NMR spectrum was an increase in the amplitude of the Pi peak, which was maximal in the first 10 min period, whilst the blood pressure was at its minimum
The changes in MRS parameters and reduction in Mean Arterial Blood Pressure (MABP) were not reversed during the 80min period of study, consistent with the long half life of this drug
Summary
The aim of the study was to relate changes in NMR parameters to changes in blood pressure
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