Acute exercise and gender alter cardiac autonomic tonus differently in hypertensive and normotensive rats.

Arterial pressure (AP), heart rate (HR), cardiac sympathetic tonus (ST), and parasympathetic tonus (PT) were determined in spontaneously hypertensive rats (SHR, 8 male and 8 female) and Wistar-Kyoto normotensive rats (WKY, 8 male and 12 female) before and after acute exercise. Before exercise, hypertensive rats (regardless of gender) had an increased ST (+15 beats/min), increased resting HR (+12 beats/min), and decreased PT (-11 beats/min). Similarly, female rats (regardless of strain) also had an increased ST (+15 beats/min), increased resting HR (+39 beats/min), and decreased PT (-14 beats/min). Hypertensive rats had a significant reduction in AP (-17 +/- 3 mmHg), ST (-26 beats/min), PT (-7 beats/min), and HR (-14 beats/min) after exercise. In contrast, AP was not reduced in normotensive rats and ST (+18 beats/min) and HR (+42 beats/min) were increased in female normotensive rats after exercise. However, male normotensive rats had a postexercise reduction in ST (-14 beats/min) and HR (-19 beats/min). In summary, AP, ST, and resting HR were higher whereas PT was lower in hypertensive vs. normotensive rats. Furthermore, females had a higher resting HR, intrinsic HR, and ST and lower PT than male rats. These data demonstrate that gender and the resting level of AP influence cardiac autonomic regulation.