Exercise training fails to modify arterial baroreflex sensitivity in ovariectomized female rats

In men, exercise training attenuates age-related reduction in baroreflex sensitivity, which is related to cardiovascular health. It is unknown, however, if this holds true for post-menopausal women. We examined the effects of exercise training on baroreceptor-heart rate (HR) reflex sensitivity in ovariectomized (OVX) and sham-operated (SO) Wistar-Kyoto rats. At the age of 8 weeks, OVX and SO rats were assigned to either sedentary or exercise-trained group. Exercise training was performed on a treadmill 5 days per week. At the age of 20 weeks, baroreflex sensitivity in response to increases in blood pressure (BRSinc) and decreases in blood pressure (BRSdec) were evaluated by injections of phenylephrine and sodium nitroprusside, respectively. Both BRSinc and BRSdec were significantly reduced in sedentary OVX rats compared with sedentary SO rats. Exercise training decreased resting HR and BRSdec, but had no effect on BRSinc in SO rats. In OVX rats, exercise training decreased resting HR but modified neither BRSdec nor BRSinc. We conclude that withdrawal of female sex hormones in normotensive female rats is associated with reduced baroreflex sensitivity in response to both increase and decrease in blood pressure and that exercise training fails to modulate the decline of BRSinc associated with withdrawal of female sex hormones. To maintain high level of BRSinc in post-menopausal women, hormone replacement therapy may be needed.