Interaction between exercise and hypertension in spontaneously hypertensive rats: a meta-analysis of experimental studies

Abstract

The effect of exercise on the progression of hypertension and development of heart failure has been extensively studied in spontaneously hypertensive rats (SHRs), but results published thus far have not revealed a clear picture. Studies differ with respect to the age and sex of rats, duration of exercise and exercise protocols. This study was aimed to examine the influence of age at the start of exercise and the effect of the duration of exercise on blood pressure and hypertrophy, which has not been previously investigated. We identified 18 reports in the literature (with a total of about 410 rats) that investigated the effect of exercise on SHR. A reduction in blood pressure was observed in rats that started exercise protocols in the pre-hypertensive or very early hypertensive state, but not in older rats. Exercise lowered the heart weight-to-body weight ratio in rats starting exercise at a very early age, but not in rats at an advanced age. A reduction in blood pressure was observed in animals that had a short period of training, but the effect was lost when the duration of exercise was prolonged. Exercise reduced resting heart rates in all groups and increased the heart weight-to-body weight ratio in groups that were exposed to free running wheels, but not in rats that performed treadmill exercise. In conclusion, exercise per se does not reduce blood pressure in SHR with established hypertension and may increase the incidence of myocardial hypertrophy, depending on the form of exercise.

Effect of gender on training-induced vascular remodeling in SHR

“…These results agree with those reported by other authors who have evaluated the effects of exercise training in hypertensive humans (40,41,46,47) and animals (2,39). We have also shown that a training-induced MAP fall was strongly associated with both remodeling of skeletal muscle arterioles (normalization of wall-to-lumen ratio) and a reduction of rela-www.bjournal.com.br Braz J Med Biol Res 44(9) 2011 tive hind limb resistance, which were respectively elevated and significantly high in sedentary male SHR compared to age-matched WKY controls (22,25).…”

“…These investigators also concluded that the blood pressure-lowering effect was higher when training started during the pre-hypertensive phase or at an early stage, being in this case independent of exercise duration. Considering only young rats in the hypertensive stage, it was also shown that prolonged exercise protocols caused a greater pressure reduction (39). These results confirmed several previous observations by our group regarding the effectiveness of exercise training in reducing blood pressure in males but not in females (22)(23)(24)(25)(26).…”

“…As commented above, training was unable to change the wall-to-lumen ratio of non-exercised tissues, and therefore there was no reduction in total peripheral resistance and no pressure fall (24,26). Recently, Schlüter et al (39) published an elegant meta-analysis confirming that sex, age and exercise duration do interfere with the blood pressure response to exercise. It was concluded that 2-month-old SHR submitted to 3 months of treadmill training presented a differential response of systolic blood pressure: a 14-mmHg reduction in males vs 1-mmHg fall in females.…”

“…In addition to a pressure fall, a heart rate reduction is also present in male and female SHR, in other animal models as well as in human hypertension (2,3,5,25,26,34,(36)(37)(38)(39)(40)(41). Indeed, resting bradycardia is an important marker of exercise training.…”

“…Aerobic training is currently recommended as a potent coadjuvant of the pharmacological treatment of hypertension, mainly because it attenuates (but does not normalize) resting blood pressure in hypertensive animals (2,22,23,25,(34)(35)(36)(37)(38)(39) and humans (40,41).…”