CHANGES IN MICROREGIONAL PERFUSION, OXYGENATION, ATP AND LACTATE DISTRIBUTION IN SUBCUTANEOUS RAT-TUMORS UPON WATER-FILTERED IR-A HYPERTHERMIA

The effect of hyperthermia on microcirculatory and metabolic parameter s in s.c. DS-sarcomas of different sizes on the hind foot dorsum of SD -rats was investigated. Hyperthermia was carried out using a novel wat er-filtered, infrared-A radiation technique. Heating was performed at a rate of 0.5 degrees C/min until 44 degrees C was achieved in the tum our centre, which was maintained for 60 min. Using a multichannel lase r Doppler flowmeter, red blood cell flux could be assessed continuousl y and at several sites within the tumour tissue simultaneously. Substa ntial inter-site variations in laser Doppler flux (LDF) were observed during hyperthermia which were independent of tumour size, site of mea surement, and temperature at the site of measurement, indicating that single site measurements of tumour LDF are poor predictors of the mean response of a tumour to hyperthermia. When mean LDF was considered, d ecreases in red blood cell fluxes occurred that were more pronounced t he greater the tumour volume. In no case was vascular stasis observed. Hyperthermia did not affect tumour oxygenation substantially. Microre gional and global assessment of lactate and ATP concentrations demonst rated increased lactate and decreased ATP levels following hyperthermi a. Tumour glucose levels were increased following hyperthermia, possib ly due to an enlarged distribution space resulting from development of interstitial. oedema. Changes in lactate and ATP levels and the lack of changes in tumour oxygenation suggest a modification of energy meta bolism following hyperthermia in the form of increased ATP hydrolysis, intensified glycolysis and impaired oxidative phosphorylation.