Cardiovascular Responses to Alpha Adrenergic Agents in Chronically-Exercised Spontaneously Hypertensive Rats

The influence of treadmill exercise training on cardiovascular regulation was investigated in spontaneously hypertensive rats (SHR) of Okamoto strain during their 8th to 18th week of life. Non-exercising age-matched SHR and Wistar-Kyoto (WKY) rats served as cage controls. Resting systolic blood pressure (SBP), heart rate (HR) and weight changes were measured in the three groups during the training period. At the completion of the training period (week 18), the trained SHR had SBP values of 164 +/- 4 mm Hg and HR values of 388 +/- 8 beats per minute, which were significantly less than (P less than 0.05) those values recorded for the control SHR (SBP = 186 +/- 3 mm Hg; HR = 422 +/- 11 bpm). The influence of exercise on baroreceptor regulation of HR was evaluated in anesthetized animals from all three groups. Phenylephrine-induced increases in mean arterial blood pressure (MAP) produced significantly greater (P less than 0.05) reflex decreases in HR in the trained SHR versus the sedentary SHR. No significant difference in baroreflex sensitivity values were noted between the WKY and trained SHR. Additionally, norepinephrine infusion produced significantly smaller (P less than 0.05) pressor responses in trained versus sedentary SHR. We conclude that exercise training significantly reduces resting SBP and HR while modifying the baroreceptor regulation of HR and cardiovascular responses to adrenergic agents in the SHR.