Cardiovascular responses to exercise and stress in the borderline hypertensive rat.

This report demonstrates the effect of voluntary exercise in attenuating increases in heart rate (HR) caused by chronic stress in an animal model of stress-induced hypertension, the borderline hypertensive rat (BHR). Exercise training also protected against the hypertensive effects of stress in 16-wk-old, but not 10-wk-old animals. In the first experiment, adult borderline hypertensive rats were subjected to 1 wk of signaled shock followed by 6 wk of signaled, unsignaled, or no shock. Half of these animals also had free access to a running wheel. Blood pressure (BP) and HR were measured before and after treatments by the tail cuff method. Exercise was found to significantly attenuate the rise in BP by 56% and HR by over 100%, as compared to non-exercised animals. In a second study, borderline hypertensive rats were subjected daily to anticipation of shock or handling for 6 wk. Half of these animals could exercise voluntarily. BP and HR, measured weekly under light ether anesthesia, increased over time due to both stressors alone. Exercise attenuated stress-induced increases in HR by 50%, but did not attenuate BP. These studies demonstrate that voluntary exercise can reliably attenuate increases in HR regardless of age or concurrent stress, but the protective effects of exercise on stress-induced hypertension may interact with the age of the subject.