ABC | Volume 112, Nº5, May 2019

Original Article Thermoregulation in Hypertensive Rats during Exercise: Effects of Physical Training Luis Henrique Lobo Silame Gomes, 1 L ucas Rios Drummond, 2 Helton Oliveira Campos, 2 Leonardo Mateus Teixeira de Rezende, 1 M iguel Araújo Carneiro-Júnior, 1 Alessandro Oliveira, 3 A ntônio José Natali, 1 Thales Nicolau Prímola-Gomes 1 Universidade Federal de Viçosa (UFV), 1 Viçosa, MG – Brazil Universidade Federal de Minas Gerais (UFMG), 2 Belo Horizonte, MG – Brazil Universidade Federal de São João del-Rei, 3 São João del-Rei, MG – Brazil Mailing Address: Thales Nicolau Prímola Gomes • Universidade Federal de Viçosa - Departamento de Educação Física, Av. Ph. Rolfs, s/n. Postal Code 36570-000, Campus Universitário, Viçosa, MG – Brazil E-mail: thales.gomes@ufv.br, thalesprimola@gmail.com Manuscript received April 23, 2018, revised manuscript August 15, 2019, accepted August 15, 2019 DOI: 10.5935/abc.20190050 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 core 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. (Arq Bras Cardiol. 2019; 112(5):534-542) Keywords: Rats; Hypertension; Exercise/physiology; Physical Exertion; Body Temperature Changes; Fatigue. Introduction During exercise, elevation of core temperature (Tcore) results from an imbalance between heat production and dissipation, since heat production increases exponentially before the mechanisms of heat dissipation are activated. 1,2 Hyperthermia may be a sign that individuals will reach fatigue and interrupt exercise, and hence an adequate control of the Tcore is critical for maintenance of physical performance. 3 Arterial hypertension is a public health problem in the world and considered one of the main risk factors for cardiovascular diseases. 4 Among the experimental models used in studies on the pathophysiology of arterial hypertension, the spontaneously hypertensive rats (SHR) is the most commonly used. Similar to humans, SHR develop progressive left ventricular hypertension in response to blood pressure elevation and to increased peripheral vascular resistance. 5,6 In recent studies of our group, we observed that untrained SHR showed disturbances in the regulation of body temperature during acute physical exercise. During exercise, hypertensive animals showed lower heat dissipation and higher heat production, leading to marked increase in Tcore compared with normotensive animals. 7,8 This was associated with lower mechanical efficiency (ME) in hypertensive animals. 7 Several benefits of aerobic physical training have been demonstrated in hypertensive individuals, including reduction of blood pressure, improvement of cardiac function, and reduction in total peripheral resistance. 9,10 However, the effects of low-intensity, aerobic physical training on thermal balance in hypertensive animals have not been investigated. Thus, the present study aimed to evaluate the effects of low‑intensity physical training on thermal balance of hypertensive rats subjected to an acute physical exercise protocol. We tested the hypothesis that low-intensity exercise could promote positive adaptations and reversal of the effects on the thermal balance in SHRs. Methods Experimental animals Sixteen-week-old normotensive Wistar rats and SHR were randomly stratified into four groups: control Wistar rats (C-WIS, 534