Participação do óxido nítrico central nos ajustes termorregulatórios durante o exercício físico em ratos espontaneamente hipertensos: efeitos do treinamento físico

Abstract

Thermoregulation occurs by a balance between the mechanisms of heat production and dissipation of the body. The increased availability of nitric oxide (NO) appears to increase heat dissipation and decrease heat storage during exercise. Spontaneously hypertensive rats (SHR) present an imbalance in the regulation of body temperature during physical exercise that may be related to the level of activation of NO-modulated neural pathways. Since physical training could correct thermoregulatory imbalance in SHRs via modulation of central oxynitrogenic pathways, this study aimed to verify if the thermoregulatory deficit presented by hypertensive animals during exercise involves the activation of neural pathways modulated by nitric oxide and which would be the possible effects of physical training on this thermoregulatory control. We used 38 normotensive Wistar rats (NWRs) and 30 SHRs divided into 4 experimental protocols. In the first experimental protocol, the objective was to verify if thermoregulatory deficit presented by hypertensive animals during the exercise would involve changes in the central nervous system. In the second experimental protocol, the objective was to determine the central injection dose of sodium nitroprusside (NPS, a nitric oxide donor) more suitable for the experiments involving thermoregulation during exercise. In the third experimental protocol, the objective was to study the effects of increased NO availability in the central nervous system on the thermal balance during exercise and on physical performance in normotensive and hypertensive rats. In the fourth experimental protocol, the objective was to evaluate the effects of physical training in hypertensive and normotensive rats on the thermal balance during exercise, on the protein expression of neuronal nitric oxide synthase in central nervous system areas involved in thermoregulation during exercise. The results of the study indicate that hypertensive animals present a lower heat dissipation during exercise, which generates greater increases in internal temperature. The difficulty of hypertensive animals in dissipating heat during exercise is, at least in part, related to central mechanisms. Reduced activations of brain nuclei involved in thermoregulation are related to a high threshold for heat dissipation found in hypertensive animals. The dose of 8.4 mmol showed the most adequate dose among those tested to evaluate the effects of NPS on thermoregulation during exercise. Increased central NO availability increases heat dissipation and decreases hyperthermia during exercise in normotensive and hypertensive rats. In addition, physical training increases the efficiency ofthermoregulatory control during exercise in normotensive and hypertensive animals and the increase in this efficiency can be explained by an increase in the activity of neuronal nitric oxide synthase in trained animals. The results of present study allow us to conclude that the thermoregulatory changes found between hypertensive and normotensive animals during exercise originated in the central nervous system. In addition, physical training increases the efficiency of thermoregulatory control during exercise in normotensive and hypertensive animals by increasing the availability of NO in the central nervous system.