We hypothesized that lumbar sympathetic nerve activity (LSNA) increases at the onset of whole-body dynamic exercise in the rat. To test this hypothesis, we recorded LSNA, heart rate (HR), and arterial pressure (AP) at rest and during a graded exercise test in six adult rats. Rats were instrumented with arterial and venous catheters and recording electrodes around the lumbar sympathetic trunk. Following recovery, each rat ran continuously on a hand-driven or motorized treadmill at 6 m·min-1, 12 m·min-1, and 18 m·min-1 on a 10% grade for approximately 3 min at each workload. Before exercise, mean arterial pressure(MAP), HR, and LSNA averaged 108 ± 4 mm Hg, 385 ± 20 bpm, and 100%, respectively. As hypothesized, all variables increased abruptly and dramatically at the onset of treadmill exercise. For example, MAP (117± 5 mm Hg), HR (450 ± 15 bpm), and LSNA (225 ± 19%) all increased significantly within the first 25 s of treadmill running at 6 m·min-1. As the exercise continued, there was a progressive increase in HR; however, MAP plateaued at 6 m·min-1 and LSNA plateaued at 12 m·min-1. Since LSNA increased at the onset of whole-body dynamic exercise in the rat, we suggest that the increase in LSNA at the onset of exercise is mediated by a central (feed forward) mechanism.
Department of Physiology, Northeastern Ohio Universities, College of Medicine, Rootstown, OH 44272
Submitted for publication August 1995.
Accepted for publication February 1996.
We appreciate the excellent secretarial work of Karen Greene, Department Assistant in Physiology, in the preparation of this manuscript. We would also like to thank the expert reviewers for the time and effort contributed to strengthening our manuscript.
This work was supported by National Heart, Lung, and Blood Institute Grant HL-45245.
Address for correspondence: Stephen E. DiCarlo, Ph.D., Department of Physiology, Northeastern Ohio Universities, College of Medicine, 4209 State Route 44, P.O. Box 95, Rootstown, OH 44272. E-mail:firstname.lastname@example.org.