Brain Temperature in Spontaneously Hypertensive Rats during Physical Exercise in Temperate and Warm Environments

This study aimed to evaluate brain temperature (T-brain) changes in spontaneously hypertensive rats (SHRs) subjected to two different physical exercise protocols in temperate or warm environments. We also investigated whether hypertension affects the kinetics of exercise-induced increases in Tbrain relative to the kinetics of abdominal temperature (T-abd) increases. Male 16-week-old normotensive Wistar rats (NWRs) and SHRs were implanted with an abdominal temperature sensor and a guide cannula in the frontal cortex to enable the insertion of a thermistor to measure T-brain. Next, the animals were subjected to incremental-speed (initial speed of 10 m/min; speed was increased by 1 m/min every 3 min) or constant-speed (60% of the maximum speed) treadmill running until they were fatigued in a temperate (25 degrees C) or warm (32 degrees C) environment. T-brain, T-abd and tail skin temperature were measured every min throughout the exercise trials. During incremental and constant exercise at 25 degrees C and 32 degrees C, the SHR group exhibited greater increases in T-brain and T-abd relative to the NWR group. Irrespective of the environment, the heat loss threshold was attained at higher temperatures (either Tbrain or Tabd) in the SHRs. Moreover, the brain-abdominal temperature differential was lower at 32 degrees C in the SHRs than in the NWRs during treadmill running. Overall, we conclude that SHRs exhibit enhanced brain hyperthermia during exercise and that hypertension influences the kinetics of the T-brain relative to the Tabd increases, particularly during exercise in a warm environment.