Blunted centrally mediated sympathoexcitation in exercise trained rats.

Exercise training (ExTr) has been shown to attenuate baroreflex mediated sympathoexcitation in various animal models. We have shown previously that direct excitation of the rostral ventrolateral medulla with glutamate microinjections also results in reduced sympathoexcitation in ExTr rats. These data suggest that blunted sympathoexcitation may not be specific to the arterial baroreflex. Therefore, we hypothesized that exercise training results in a reduction in centrally mediated reflex sympathoexcitation. To test this hypothesis, treadmill trained rats (ExTr, 8–10 wks) or sedentary controls (Seds) were anesthetized with Inactin, paralyzed, and instrumented to record mean arterial pressure (MAP) and lumbar sympathetic nerve activity (LSNA). In order to produce a centrally mediated reflex sympathoexcitation, the somatopressor reflex was elicited by stimulation of the central cut end of the sciatic nerve (0.1–1mA, 1 ms, 15 Hz) for 10 s. Sciatic nerve stimulation produced intensity dependent increases in MAP and LSNA in both groups. However, increases in LSNA were blunted in ExTr animals by 60% or more at all intensities tested. These experiments suggest that ExTr reduces centrally mediated sympathoexcitation. Along with previous work these data suggest that blunted sympathoexcitation may involve altered EAA mechanisms at the level of the RVLM. These centrally mediated alterations likely impact cardiovascular regulation in ExTr individuals and may contribute to the beneficial effects of ExTr by lowering reflex mediated increases in SNA. (Supported by HL‐55306).