Post-exercise elevations in sympathetic nerve activity and baroreflex function in normotensive rabbits

We tested the hypothesis that a single bout of dynamic exercise reduces postexercise arterial pressure, heart rate, and renal sympathetic nerve activity and attenuates the arterial baroreflex control of heart rate and renal sympathetic nerve activity in normotensive New Zealand White rabbits. Animals were chronically instrumented with right jugular venous and left femoral arterial catheters, and electrodes around the renal sympathetic nerve. Arterial pressure, heart rate, and renal sympathetic nerve activity were recorded for two hours pre-exercise and two hours after a single bout of treadmill exercise (post-exercise). Post-exercise heart rate, arterial pressure, and renal sympathetic nerve activity were elevated above pre-exercise values (71+/-3 bpm, 13+/-1 mmHg, and 80+/-21% respectively). These data demonstrate that normotensive rabbits do not exhibit post-exercise hypotension, due in part to elevations in sympathetic nerve activity. In addition, arterial baroreflex regulation of heart rate and renal sympathetic nerve activity were determined pre- and post-exercise. Exercise shifted the baroleflex function curve for heart rate and renal sympathetic nerve activity upward and to the right without a change in gain. These data suggest that post-exercise elevations in sympathetic nerve activity are due, in part, to an elevation of the operating point of the arterial baroreflex to a higher pressure. These responses in normotensive rabbits contrast sharply with the responses in hypertensive individuals and animals. Understanding the mechanisms contributing to the differences between hypertensive and normotensive subjects may lead to measures designed to lower arterial pressure in hypertensive individuals.