Thermoregulation in Hypertensive Rats during Exercise: Effects of Physical Training

Abstract

Background: Spontaneously hypertensive rats (SHR) show deficit in thermal balance during physical exercise.

Objective: To assess the effects of low-intensity physical exercise training on thermal balance of hypertensive rats undergoing an acute exercise protocol.

Methods: Sixteen-week-old male Wistar rats and SHR were allocated into four groups: control Wistar rats (C-WIS), trained Wistar (T-WIS), control SHR (C-SHR) and trained SHR (T-SHR). Treadmill exercise training was performed for 12 weeks. Blood pressure, resting heart rate and total exercise time was measured before and after the physical exercise program. After the exercise program, a temperature sensor was implanted in the abdominal cavity, and the animals subjected to an acute exercise protocol, during which internal body temperature, tail skin temperature and oxygen consumption until fatigue were continuously recorded. Mechanical efficiency (ME), work, heat dissipation threshold and sensitivity were calculated. Statistical significance was set at 5%.

Results: Physical training and hypertension had no effect on thermal balance during physical exercise. Compared with C-WIS, the T-WIS group showed higher heat production, which was counterbalanced by higher heat dissipation. Hypertensive rats showed lower ME than normotensive rats, which was not reversed by the physical training.

Conclusion: Low-intensity physical training did not affect thermal balance in SHR subjected to acute exercise.

Figure 1

Internal body temperature (CBT, A), oxygen consumption (VO₂, B) and tail skin temperature (T_skin, C) during acute exercise, until fatigue. Control Wistar (C-WIS), trained Wistar (T-WIS), control SHR (C-SHR), trained SHR (T-SHR). Data expressed as mean ± SD; * p < 0.05: C-SHR vs. C-WIS; # p < 0.05: T-WIS vs. C-WIS; + p < 0.05: T-SHR vs. T-WIS.

Figure 2

Heat dissipation threshold (ºC) (A) and sensitivity (B) during the acute physical exercise protocol. Data expressed as mean ± SD. C-WIS: control Wistar, T-WIS: trained Wistar, C-SHR: control SHR, T-SHR: trained SHR.

Figure 3

Work (W, A) and mechanical efficiency (ME, B) during the acute physical exercise protocol. Data expressed as mean ± SD; * p < 0.05: C-SHR vs. C-WIS; + p < 0.05: T-SHR vs. T-WIS. C-WIS: control Wistar, T-WIS: trained Wistar, C-SHR: control SHR, T-SHR: trained SHR.

Figure 4

Heat accumulation (HA, A) and heat accumulation/work ratio (HA/W, B). Data expressed as mean ± SD; # p < 0.05: T-WIS vs. C-WIS. + p < 0.05: T-SHR vs. T-WIS, C-WIS: control Wistar, T-WIS: trained Wistar, C-SHR: control SHR, T-SHR: trained SHR.