Running training attenuates blood pressure and norepinephrine responses to immobilization stress in spontaneously hypertensive rats
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We investigated the effects of 4 weeks of running training on the progressive changes in resting blood pressure (BP) and heart rate (HR) that occurred during that period, as well as on the increases in cardiovascular variables and catecholamine levels induced by a novel stress (immobilization stress) in spontaneously hypertensive rats (SHR) and control normotensive Wistar-Kyoto rats (WKY). In addition, rat sensitivity to exogenously infused norepinephrine (NE) was investigated by measuring the induced pressor response. BP was measured by a tail-cuff method (without heating), which is reportedly both sensitive and accurate for noninvasive measurement of BP in conscious rats. Increases in resting systolic BP over the 4-week period were significantly smaller in the trained SHR than in the untrained SHR, but the training had no effect on the changes in resting BP seen in WKY. After the 4-week running training, BP and NE responses to immobilization stress were reduced in the SHR, as was the increase in BP induced by intravenous (IV) infusion of NE. In the WKY, however, neither the BP response to the stress nor that to the IV infusion of NE was changed by running training. These results suggest 1) that such training was beneficial in the SHR, and 2) that the immobilization stress-induced activation of the sympathetic nervous system (as evidenced by the increase in plasma NE) and the sensitivity to NE (as evidenced by the increase in BP induced by exogenous NE) were each attenuated after the 4-week running training in the SHR, with a consequent reduction in the BP response to a novel stress.