Spontaneously hypertensive rats have greater impairments in regulating abdominal temperature than brain cortex...

This study aimed to evaluate the changes in brain (T_brain) and abdominal (T_abd) temperatures in spontaneously hypertensive rats (SHRs) following fatiguing exercise. Male normotensive Wistar rats (NWRs) and SHRs were used at 16 weeks of age. Their arterial pressure was measured by tail plethysmography prior to the experiments to confirm the hypertensive status of the SHRs. Then, the rats underwent implantation of an abdominal temperature sensor to measure T_abd and a guide cannula in the frontal cortex to enable the insertion of a thermistor to measure T_brain. After a familiarization period, each animal was subjected to incremental speed exercises until fatigue in either a temperate (25 °C) or warm (32 °C) environment, followed by a 60-min post-exercise period at the same temperature at which they exercised. T_brain, T_abd and tail-skin temperature (T_skin) were measured every min throughout the experiments. SHRs exhibited higher T_abd values than NWRs, and these higher values were transiently and persistently observed at 25 °C and 32 °C, respectively. For example, at 32 °C, T_abd was 0.84 °C higher in SHRs at the 25th min (large effect size). In contrast, regardless of the ambient temperature, SHRs exhibited similar T_brain values as NWRs, indicating preserved T_brain regulation following exercise in hypertensive rats. SHRs presented higher T_skin during the last half of the post-exercise period at 25 °C, whereas no inter-group differences were observed at 32 °C. In conclusion, the present results highlight that SHRs, an animal model that mimics uncontrolled essential hypertension in humans, exhibited greater impairments in regulating T_abd than T_brain during the post-exercise period.