To study the effects of hyperthermia, alone and in conjunction with microwave exposure, on brain energy metabolism (reflected in brain ATP and CP (creatine phosphate)-concentration) in rats. The effect of temperature on ATP and CP was determined in the brains that were maintained at 35.6, 37, 39, and 41°C.
|Exposure duration||0.5, 1.0, 3.0 and 5.0 min|
|power density||138 W/m²||unspecified||measured||-||-|
At 37, 39, and 41°C brain ATP concentration was down 6, 10.8, and 29.2% from the 35.6°C control concentration and creatine phosphate concentration was 19.6, 28.7, and 44% from the 35.6°C control concentration. Irradiation of the brain to 591 MHz (13.8 mW/cm²) for 0.5, 1, 3, and 5 min caused further decreases (below those observed for hyperthermia only) of 16, 29.8, 22.5, and 12.3% in brain ATP concentration, and of 15.6, 25.1, 21.4, and 25.9% in brain creatine phosphate concentration. Recording of brain NADH fluorescence before, during, and after microwave irradiation showed an increase in NADH fluorescence during microwave exposure that returned to preexposure levels within 1 min postexposure. Continuous recordings of brain temperatures during exposures showed that brain temperature varied between -0.1 and +0.05°C. So the microwave irradiations did not induce tissue hyperthermia, and it is concluded that direct microwave interaction at the subcellular level is responsible for the observed decrease in ATP- and CP-concentration.