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Abstract
This study aimed to evaluate brain temperature (Tbrain) 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 (Tabd) 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 Tbrain. 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°C) or warm (32°C) environment. Tbrain, Tabd and tail skin temperature were measured every min throughout the exercise trials. During incremental and constant exercise at 25°C and 32°C, the SHR group exhibited greater increases in Tbrain and Tabd 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°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 Tbrain relative to the Tabd increases, particularly during exercise in a warm environment.
Highlights
Hypertension is a multifactorial clinical condition characterized by high, sustained blood pressure, often in association with functional and/or structural changes in target organs [1, 2]
In response to incremental running at 32°C (Fig 2), the spontaneously hypertensive rats (SHRs) exhibited a greater increases in Tbrain than the normotensive Wistar rats (NWRs) from the 7th until the 14th min and at volitional fatigue (39.88 ± 0.16°C vs. 39.45 ± 0.17°C, p < 0.05)
Tbrain control was evaluated in SHRs during physical exercise in temperate and warm environments
Summary
Hypertension is a multifactorial clinical condition characterized by high, sustained blood pressure, often in association with functional and/or structural changes in target organs [1, 2]. As evidenced by epidemiological studies, the incidence of heat-related illness is higher in hypertensive subjects during heat waves in the United States of America and Europe [3,4,5]. This observation indicates that hypertension may compromise thermoregulation and thermal tolerance in subjects affected by this disease. We observed a greater increase in the abdominal temperature (Tabd) of SHRs subjected to physical exercise in a warm environment This exaggerated hyperthermia was consequent to reduced mechanical efficiency, which means that SHRs exhibited greater oxygen consumption and, greater heat production than normotensive rats when running at the same treadmill speed [13]
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